SYSTEM AND METHOD FOR AFFECTING THE SURFACE OF A CONDUCTIVE MATERIAL - Patent application

Abstract

Systems and methods are described for beneficially influencing the surface morphology of conductive materials using electrochemistry. The systems and methods for beneficially influencing the surface morphology of conductive materials use a bimodal process in which a first current type (AC or DC) is applied to an electrolyte between an electrode and a workpiece, followed by a second current type that is different from the first current type used. The bimodal process can be repeated one or more times.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 343,933, filed May 19, 2022, entitled "SYSTEMS AND METHODS FOR AFFECTING SURFACES OF ELECTRICALLY CONDUCTIVE MATERIALS," the entirety of which is incorporated herein by reference.

[0002] (Technical field) The technology described herein generally relates to systems and methods for beneficially affecting the surface morphology of a conductive material using electrochemistry. More particularly, the technology described herein relates to systems and methods for beneficially affecting the surface morphology of a conductive material using a bimodal process, in which a first current type (AC or DC) is applied to an electrolyte between an electrode and a workpiece, followed by a second current type that is different from the first current type used. The bimodal process can be repeated one or more times. [Background technology]

[0003] Electrochemical methods of affecting the surface of materials are primarily based on Faraday's law of electrolysis. In essence, the result of an electrochemical operation is directly proportional to the charge introduced into the system. If the polarity of the electrodes is kept constant, the change in said electrodes can be predicted by the charge introduced. In the example of electrodeposition, for a total number of electrons flowing into the system (typically measured in ampere-hours), a defined number of cationic species will be deposited on the electrode of interest. If these cations are deposited, how evenly they are distributed, and the functional and aesthetic properties of the deposit are controlled by other factors.

[0004] In reality, there is a rate-limiting step for these results, which is mainly influenced by mass transport mechanisms around the electrode. Again using the example of electrodeposition, when metal is deposited on an electrode, the replenishment of new ionic species to the workpiece is constrained by the diffusion, convection, and transport methods of the actual chemical solution in a significantly thin interfacial layer. Diffusion, the random movement of molecules from areas of high concentration to areas of lower concentration, creates an obstacle to the uniform distribution of chemical species within this layer, resulting in an impediment barrier. Similarly, fluid forces within an electrochemical cell, either from mechanical agitation / mixing or differential heat transfer, can improve the efficiency of mass transfer, but localized excessive turbulence or laminar flow can also create a barrier to overcome. Finally, the movement of charged particles flowing in a localized electric field that creates a concentration gradient of ionic species is a further component to the impediment barrier.

[0005] These constraints around the working electrode will result in undesirable results unless operational boundaries are imposed on the operating parameters. Continuing with the example of electrodeposition, if the rate of charge is introduced too fast, uneven and even uncontrolled deposition of ionic species will occur. Conversely, if the rate of charge is introduced too slowly, chemical degradation of the deposits may be encountered due to the chemistry of the electrolyte itself. A typical result is chemical attack, often in the form of unwanted and detrimental pitting of the electrodes.

[0006] Advances in the technical field of electrochemical operations since Faraday introduced the laws of electrolysis have mainly focused on developing or evolving the properties of the chemical species involved or enhancing mechanical methods to overcome problems in impeding barriers. Various chemical species have been discovered and introduced that beneficially affect the electrochemical results, such as surfactants and complexing agents. Furthermore, mechanical methods of solution mixing or concentration of solution chemistry delivery have also advanced over time. In particular, sparging devices have been designed and added with electrolyte delivery methods, such as those found in the field of Electrochemical Machining (ECM), for better solution mixing.

[0007] These more recent developments are generally designed to minimize the detrimental effects of slowly replenishing the barrier layer adjacent to the electrode of interest. A subset of these methods are aimed at promoting "detrimental" (i.e., roughening) surface effects on the electrode. In some outcomes, degrading or roughening the surface morphology of the electrode may have practical value. This is evidenced by the destructive outcome of "corroding" the electrode such that its surface pores or irregularities become essential for the deposition of subsequent layers. This outcome is advantageous when the material of interest, when exposed to air, rapidly forms an oxide that prevents the deposition of subsequent layers. Aluminum lithography plates are treated to detrimentally affect (i.e., roughen) the surface morphology in order to create a surface that readily accepts the application of subsequent inks. This roughened surface morphology is typically considered detrimental because it results in stress corrosion cracking, reduced fatigue life, or a requirement for the subsequent application of additional secondary layers to overcome the irregularities. There are limited applications where roughening the surface morphology provides benefit to the application.

[0008] In view of the above, further improvements in electrochemical processes that beneficially affect the surface of a workpiece remain desirable. Summary of the Invention

[0009] This Summary is provided to introduce some concepts in a simplified form that are further described below in the Detailed Description. This Summary, and the preceding Background, are not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended to be used as an aid in determining the scope of the claimed subject matter.

[0010] In some embodiments, a bimodal method of affecting a surface of a conductive workpiece is disclosed. The method may include immersing a surface of a conductive metal workpiece in an electrolyte solution; immersing at least a surface of an electrode in the electrolyte solution; initiating a first mode of operation, the first mode of operation including either applying a direct current to the electrolyte solution between the conductive metal workpiece and the electrode or applying an alternating current to the electrolyte solution between the conductive metal workpiece and the electrode; terminating the first mode of operation; initiating a second mode of operation, the second mode of operation including either applying an alternating current to the electrolyte solution between the conductive metal workpiece and the electrode or applying a direct current to the electrolyte solution between the conductive metal workpiece and the electrode, the second mode of operation using a different current type than the first mode of operation; and terminating the second mode of operation. The first mode of operation and the second mode of operation may be performed one or more times in succession. The material of the conductive metal workpiece may include: (1) pure Ti, Zr, Nb, Hf, Ta, or V, or Ti-, Zr-, Nb-, Hf-, Ta-, or V-based alloys; (2) pure Ni, Ni-, Co-, or titanium aluminides; (3) austenitic stainless steel; (4) martensitic stainless steel; (5) ferritic stainless steel, carbon steel, or alloy steel; (6) pure aluminum or aluminum alloy; or (7) pure copper or copper alloy.

[0011] In some embodiments, a system for affecting a surface of a conductive metal workpiece is disclosed. The system may include an electrolyte bath; a conductive metal workpiece, at least one surface of which is immersed in the electrolyte bath; an electrode, at least one surface of which is immersed in the electrolyte bath; a DC power supply, a first end of which is connected to the conductive metal workpiece and a second end of which is connected to the electrode; and an AC power supply, a first end of which is connected to the conductive metal workpiece and a second end of which is connected to the electrode. The system is configured such that in a first mode of operation, the DC power supply either applies only direct current to the electrolyte solution between the conductive metal workpiece and the electrode or the AC power supply applies only alternating current to the electrolyte solution between the conductive metal workpiece and the electrode, and in a second mode of operation, the AC power supply either applies only alternating current to the electrolyte solution between the conductive metal workpiece and the electrode or the DC power supply applies only direct current to the electrolyte solution between the conductive metal workpiece and the electrode. The system is further configured such that the first mode of operation uses a different current type than the second mode of operation. In operation, the system cycles between the first mode of operation and the second mode of operation. The material of the conductive metal workpiece may include: (1) pure Ti, Zr, Nb, Hf, Ta, or V, or Ti-, Zr-, Nb-, Hf-, Ta-, or V-based alloys; (2) pure Ni, Ni-, Co-, or titanium aluminides; (3) austenitic stainless steel; (4) martensitic stainless steel; (5) ferritic stainless steel, carbon steel, or alloy steel; (6) pure aluminum or aluminum alloy; or (7) pure copper or copper alloy.

[0012] As noted above, the methods and systems described herein are applicable to seven separate and distinct workpiece material categories. Without wishing to be bound by theory, the ability to affect these different types of materials with the bimodal application of power as described herein may be due to the nature of the behavior of the elements of the periodic table contained within the different material categories. Originally, when Mendelev constructed the periodic table, it was an attempt to arrange the elements with the most similar properties into vertical columns. Furthermore, the groups are also arranged in relation to the number of protons and correspondingly the number of electrons of the elements. Because electrons exist in a series of increasingly complex shells, as well as the Bohr model of electron behavior, the vertical groups of elements are also arranged such that each column reflects the number of electrons in their valence shell. As a result, the ability to affect and interact with these valence electrons provides a means to understand two aspects of the technology described herein. The distinctions between the material categories disclosed herein are arranged, in part, by this grouping of valence electrons. Metals such as titanium, vanadium, and niobium share similar valence electron configurations and are therefore grouped together for the purposes of the techniques described herein. Secondarily, with the bimodal application of external power sources described herein, the effects on the valence electrons can be influenced by electrochemical, electromotive, and electromagnetic properties.

[0013] These and other aspects of the technology described herein will become apparent after consideration of the detailed description and figures herein. However, the scope of claimed subject matter should be determined by the claims as issued, and not by whether a given subject matter addresses any or all of the problems discussed in the Background or includes any features or aspects recited in the Summary.

[0014] Non-limiting, non-exhaustive embodiments of the disclosed technology, including preferred embodiments, are described with reference to the following figures, in which like reference numbers refer to like parts throughout the various views unless otherwise specified. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of a system for beneficially affecting a surface of a conductive metal workpiece, configured in accordance with various embodiments described herein. [Diagram 2] 1 is a flowchart illustrating a method for beneficially affecting a surface of a conductive metal workpiece, arranged in accordance with various embodiments described herein. [Figure 3A] 1A-1D illustrate various exemplary operational schemes for methods and systems configured in accordance with various embodiments described herein. [Figure 3B] 1A-1D illustrate various exemplary operational schemes for methods and systems configured in accordance with various embodiments described herein. [Figure 4] 1 is a table summarizing grit finishes and estimated RMS and Ra values. [Figure 5A] 1 is a table summarizing data from experimental trials conducted on workpiece material category 1 - reactive metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 5B] 1 is a table summarizing data from experimental trials conducted on workpiece material category 1 - reactive metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 6A] 1 is a table summarizing data from experimental trials conducted on workpiece material category 2 - high temperature / high strength metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 6B]1 is a table summarizing data from experimental trials conducted on workpiece material category 2 - high temperature / high strength metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 6C] 1 is a table summarizing data from experimental trials conducted on workpiece material category 2 - high temperature / high strength metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 6D] 1 is a table summarizing data from experimental trials conducted on workpiece material category 2 - high temperature / high strength metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 6E] 1 is a table summarizing data from experimental trials conducted on workpiece material category 2 - high temperature / high strength metals, using systems and methods configured in accordance with various embodiments described herein. [Figure 7A] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 7B] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 7C] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 7D] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 7E]1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 7F] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 3 - austenitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 8] 1 is a table summarizing data from experimental trials conducted on workpiece material Category 4 - martensitic stainless steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 9A] 1 is a table summarizing data from experimental trials performed on workpiece material category 5 - ferritic stainless steel, carbon steel, alloy steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 9B] 1 is a table summarizing data from experimental trials performed on workpiece material category 5 - ferritic stainless steel, carbon steel, alloy steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 9C] 1 is a table summarizing data from experimental trials performed on workpiece material category 5 - ferritic stainless steel, carbon steel, alloy steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 9D] 1 is a table summarizing data from experimental trials performed on workpiece material category 5 - ferritic stainless steel, carbon steel, alloy steel, using systems and methods configured in accordance with various embodiments described herein. [Figure 10]1 is a table summarizing data from experimental trials conducted on workpiece material category 6 - aluminum and aluminum alloys, using systems and methods configured in accordance with various embodiments described herein. [Figure 11] 1 is a table summarizing data from experimental trials conducted on workpiece material category 7 - copper and copper alloys, using systems and methods configured in accordance with various embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The embodiments are described more fully below with reference to the accompanying figures, which form a part of this specification and show, by way of illustration, certain exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, the embodiments may be embodied in many different forms and should not be understood to be limited to the embodiments set forth herein. Thus, the following detailed description should not be taken in a limiting sense.

[0017] Referring to Figure 1, a system 100 for beneficially affecting a surface of a conductive metal workpiece is shown. System 100 generally includes an electrolyte solution bath 110, a conductive metal workpiece 120, an electrode 130, a DC power supply 140, and an AC power supply 150. System 100 may also optionally include a mixing device 160 (shown in Figure 1 as a mechanical mixer) and / or a heating element 170 (shown in Figure 1 as a heat exchanger).

[0018] The system 100 is configured such that at least one surface of the conductive metal workpiece 120 and at least one surface of the electrode 130 are immersed in the electrolyte bath 110. In some embodiments, most or all of the conductive metal workpiece 120 and / or most or all of the electrode 130 are immersed in the electrolyte bath 110. The minimum separation distance between the conductive metal workpiece 120 and the electrode 130 is 0.003 inches. This minimum separation distance is provided due to practical limitations. As the distance between the workpiece 120 and the electrode 130 approaches zero, there is a corresponding increase in electrical energy concentrated in an increasingly smaller volume. Theoretically, this distance can be made infinitesimal, but in practice, distances less than 0.003 inches become difficult to manage from a mass and heat transfer standpoint. Any distance greater than 0.003 inches can be used as long as electrical current can pass between the conductive metal workpiece 120 and the electrode 130.

[0019] The configuration of system 100 further includes electrical connections between each of conductive metal workpieces 120 and electrode 130 and DC power supply 140 and AC power supply 150. The particular terminals of DC power supply 140 to which each of conductive metal workpieces 120 and electrode 130 are connected are generally without limitation and may depend on the particular beneficial process being performed (electrodeposition, electrochemical removal, etc.). In some embodiments, the positive terminal of DC power supply 140 is connected to conductive metal workpiece 120 and the negative terminal of DC power supply 140 is connected to electrode 130. In some embodiments, the negative terminal of DC power supply 140 is connected to conductive metal workpiece 120 and the positive terminal of DC power supply 140 is connected to electrode 130. DC power supply 140 may also be configured to switch polarities, although the purpose of DC power supply 140 is not to provide a replacement or approximation of alternating current. The particular terminals of AC power supply 150 to which each of conductive metal workpieces 120 and electrode 130 are connected are generally not limited.

[0020] System 100 may also include a means for mixing / agitating the electrolyte bath, as appropriate. As shown in FIG. 1, mixing / agitating device 160 may be included as part of system 100 and configured to mix / agitate the electrolyte bath before, during, and / or after application of electrical current from either or both of DC power supply 140 and AC power supply 150. In some embodiments, mixing / agitating device 160 is a mechanical mixing / agitating device, such as a propeller or stir bar, although any suitable mechanical mixing / agitating device may be used. In some embodiments, mixing / agitating device 160 is a thermal mixing / agitating device.

[0021] The system 100 may also include a means for heating the electrolyte bath, as appropriate. As shown in FIG. 1, a heating device 170 may be included as part of the system 100 and configured to modify the temperature of the electrolyte bath before, during, and / or after application of electrical current from either or both of the DC power supply 140 and the AC power supply 150. The heating device 170 may be used to heat and / or cool the electrolyte bath. Any suitable heating mechanism may be used for the heating device 170, such as, but not limited to, a heat exchanger as shown in FIG. 1. Although FIG. 1 shows the heating device 170 located within the electrolyte bath solution, the heating element 170 may be located anywhere around the system 100, so long as the location of the heating element 170 allows for heating (or cooling) of the electrolyte bath solution.

[0022] For example, additional information regarding the material compositions of the workpiece 120, the electrolyte solution 110, etc., as well as the operation of the system 100 overall and individual components of the system 100 are provided below.

[0023] In application, the system 100 shown in FIG. 1 may be used to beneficially affect a surface of a conductive metal workpiece by operating in at least two modes. In a first mode of operation, the system 100 operates to apply a first type of current (e.g., direct current or alternating current) to an electrolyte bath between the conductive metal workpiece and the electrode, while in a second mode of operation, the system 100 operates to apply a second type of current, different from the first type of current, to an electrolyte bath between the conductive metal workpiece and the electrode. For example, if the first mode of operation uses direct current, the second mode of operation uses alternating current, while if the first mode of operation uses alternating current, the second mode of operation uses direct current. The system cycles between the first mode of operation and the second mode of operation one or several times, where there is no practical limit to the number of times the first and second modes of operation are performed consecutively. The modes of operation generally do not overlap, meaning that there is generally no combination of alternating current and direct current. In other words, the first mode of operation is terminated (the first current type is terminated) before the second mode of operation is initiated (the second current type is initiated). Although AC and DC are generally not used together, the time between the end of the first mode of operation and the start of the second mode of operation can be very short such that the transition from the first current type to the second current type is essentially instantaneous. Alternatively, there may be a longer period between the end of the first mode of operation and the start of the second mode of operation during which neither type of current is applied.

[0024] With reference to Figure 2, a method 200 for beneficially affecting a surface of a conductive metal workpiece is shown, where the system 100 shown in Figure 1 may be used to perform the method 200. The method 200 generally includes steps 210 of immersing at least a surface of the conductive metal workpiece in an electrolyte solution; 220 of immersing at least a surface of an electrode in the electrolyte solution; 230 of initiating a first mode of operation in which a first type of current (i.e., direct or alternating current) is applied to the electrolyte solution between the conductive metal workpiece and the electrode; 240 of terminating the first mode of operation; 250 of initiating a second mode of operation in which a second type of current, different from the first type of current, is applied to the electrolyte solution between the conductive metal workpiece and the electrode; and 260 of terminating the second mode of operation. As indicated in Figure 2 by arrow 201, steps 230, 240, 250, and 260 may be performed one or more times.

[0025] With respect to steps 210 of immersing at least a surface of the conductive metal workpiece in the electrolyte solution and 220 of immersing at least a surface of the electrode in the electrolyte solution, immersion of the workpiece and electrode can be to any level. As previously described, the workpiece can be mostly or completely immersed, or only the surfaces of the workpiece and electrode can be immersed.

[0026] The size and shape of the workpiece and electrode used in steps 210 and 220, respectively, are generally not limited.

[0027] The electrodes immersed in the electrolyte solution can be any material known to be suitable for use as electrodes and physically compatible with the material of the workpiece. In some embodiments, the electrode material provides the necessary supplemental chemical species necessary for the desired electrochemical reaction (i.e., the desired manner of favorably affecting the surface of the workpiece). In some embodiments, the electrode material is a chemically inert material. In embodiments in which the purpose of the process is to deposit material on the workpiece, the electrode can be of a material that provides the chemical species that are removed from the electrode. In embodiments in which the purpose of the process is to remove material from the workpiece, the electrode can be of a material that can accept material thereon.

[0028] The workpieces immersed in the electrolyte solution have material compositions that generally fall into one of seven different, separate categories, where each category of material potentially requires different operating parameters and / or provides different results. The seven material categories are workpieces that include: (1) pure Ti, Zr, Nb, Hf, Ta, or V, or Ti-, Zr-, Nb-, Hf-, Ta-, or V-based alloys; (2) pure Ni, Ni-, Co-, or titanium aluminides; (3) austenitic stainless steels; (4) martensitic stainless steels; (5) ferritic stainless steels, carbon steels, or alloy steels; (6) pure aluminum or aluminum alloys; or (7) pure copper or copper alloys.

[0029] The term alloy as used herein generally refers to a metallic substance composed of two or more elements as a compound or solution. When the term alloy is used in conjunction with a metal (e.g., Co-based alloys, Ni-based alloys, etc.), the specifically mentioned metal is the predominant metal present in the alloy. Predominant means the highest percentage of metallic element, and need not exceed 50%. The components of an alloy are usually metals in themselves, although carbon, a nonmetal, may be an essential component of some alloys (e.g., carbon is an essential component in steel). The distinction between alloying elements and impurities is sometimes subtle, as some elements, such as oxygen or silicon, may be considered impurities or valuable components depending on the application. The commercially recognized common names and / or associated Unified Numbering System ("UNS") numbers of the metals, when available, are associated with a particular metal or alloy to define the specific chemical composition of each metal.

[0030] As used herein, the term pure means greater than 99% by weight.

[0031] For the first workpiece material category, the workpiece includes reactive metals, where reactive metals include Ti, Zr, Nb, Hf, Ta, and V. Thus, the workpiece can be pure Ti, Zr, Nb, Hf, Ta, or V, or an alloy of any of Ti, Zr, Nb, Hf, Ta, or V. Ti-based workpieces can be made of pure titanium or titanium alloys. Titanium alloys include common titanium alloys (e.g., Ti-CP, Ti-64, Ti-10-2-3, Ti-5553, Ti-3Al-2.5V, ATI-425, Ti-Beta-C) and titanium alloys containing molybdenum and / or tin (e.g., Ti-6242, Ti-6246). Pure titanium and titanium alloys belong to the UNS R5 category and have names such as UNS R50400 (Ti-CP2) and UNS R56400 (Ti-6Al-4V). Zr-based workpieces can be made from pure Zr or Zr alloys. Pure zirconium and zirconium alloys belong to the UNS R6 category and have designations such as UNS R60802 (Zicraloy-2) and UNS R60702 (Zr 702 alloy). Nb-based workpieces can be made from pure Nb or Nb alloys. Pure niobium and niobium alloys belong to the UNS R04 category and have designations such as UNS R04210 (niobium type 2) and UNS R04261 (niobium type 4). Hf-based workpieces can be made from pure Hf or Hf alloys. Pure hafnium and hafnium alloys belong to the UNS R02 category and have the primary designation UNS R02001 (pure hafnium, or hafnium used for alloying additions in other metals). Ta-based workpieces can be made from pure Ta or Ta alloys. Pure tantalum and tantalum alloys belong to the UNS R05 category and have designations such as UNS R05255 (Ta-10W) and UNS R05240 (Ta-40Nb). V-based workpieces can be made from pure V or V alloys. Pure vanadium and vanadium alloys belong to the UNS R08 category.Commercially available grades of vanadium or vanadium alloys have not been assigned specific UNS numbers at this time.

[0032] Regarding the second workpiece material category, the workpiece includes a high temperature / high strength metal, where the high temperature / high strength metal includes pure Ni, a Ni-based alloy, a Co-based alloy, or a titanium aluminide. Ni-based workpieces can be made from pure Ni or Ni alloys (e.g., Alloy 400 UNS N04400, Alloy 600 UNS N06600, Alloy 625 UNS N06625, Alloy 685 N07001 ("Waspaloy"), Alloy 718 UNS N07718, Alloy X-750 UNS N07750, Alloy C-276 UNS N10276, Alloy C-22 UNS N06022, Alloy 617 UNS N06617, Nitinol, Rene alloys such as Rene 41 UNS N07041, Alloy 825 UNS N08825, Nimonic alloys such as Nimonic 90 UNS N07090, and variations of each). As used herein, the term Ni-based alloys should be interpreted as including Ni-based single crystal alloys, such as, but not limited to, RR2000, AM1, CMSX-2-CSMX-10, PWA1484, TMS 75, and TMS 113. Co-based alloys include X-45, FSX-414, Heines-25 UNS R30605, Heines Ultimet UNS R31233, and Co-6 UNS R30006. As used herein, the term Co-based alloys should be interpreted as including Co-based single crystal alloys. Titanium aluminide (TiAl), commonly gamma titanium, is an intermetallic compound, such as the alloy Ti-48Al-2Cr-2Nb, used in low pressure turbine blade applications.

[0033] With respect to the third workpiece material category, the workpiece is composed of austenitic stainless steels, including 303 UNS S30300, 304 UNS S30400, 316L UNS S31603, Incoloy alloys such as alloy 20 UNS N08020 and A-286 UNS S66286, Nitronic alloys such as Nitronic 40 UNS S21900 and Nitronic 60, alloy 218 UNS S21800, alumina-forming austenitic (AFA) grade alloys, X4CrNiMo16-5-1 EN1.4418 and X20CrMoV11-1 EN1.4922 (each of which contains Ni), and 420 UNS 42000 and 430 UNS 43000 (each of which does not contain Ni).

[0034] Regarding the fourth workpiece material category, the workpiece is composed of martensitic stainless steels, including 431 UNS S43100, 17-4 PH UNS S17400, X4CrNiMo16-5-1 EN 1.4418, and X20CrMoV11-1 EN1.4922 (each of which contains Ni), and 420 UNS S42000 (each of which does not contain Ni).

[0035] Regarding the fifth workpiece material category, the workpiece is composed of ferritic stainless steel, carbon steel, or alloy steel. Ferritic stainless steels include 409 UNS S40920, 410 UNS S41000, 430 UNS S43000, 439 UNS S43035, 441 UNS S44100, 434 UNS S43400, and 436 UNS S43600 (each of which contains more than 10.5% Cr). Carbon steels include low carbon steel (0.05% to 0.25% carbon by volume), medium carbon steel (0.3% to 0.5% carbon by volume), and high carbon steel (0.6% to 1.5% carbon by volume). Carbon steel grades include A36 UNS K02600, 1018 UNS G10180, a1011 and 1020 UNS G1020, 1045 UNS G10450, and A516 UNS K02700, among others. Tool steel is a subcategory of both carbon steel and alloy steel, where the carbon steel or alloy steel has high hardness and resistance to wear and deformation (generally containing 0.5% to 1.5% carbon by volume). Tool steels are classified into five groups: water-hardening tool steel, cold-working tool steel, shock-resisting tool steel, high-speed tool steel, and hot-working tool steel, UNS T00001 to UNS T99999.

[0036] For the sixth workpiece material category, the workpiece is composed of pure aluminum or aluminum alloys (UNS A00001-A99999). Al alloys have two major classifications: cast alloys and wrought alloys. Both classifications are further subclassified into heat treatable and non-heat treatable alloys. Wrought aluminum is identified with a four digit number that identifies the alloying elements. Cast aluminum alloys use four to five digits with a decimal point. In cast aluminum alloys, the hundreds digit indicates the alloying elements while the digit after the decimal point indicates the form (cast shape or ingot). All series in all product forms are considered to be within this material category. Wrought alloys are included in the 1XXX (essentially pure), 2XXX (alloyed with copper), 3XXX series (alloyed with manganese), 4XXX series (alloyed with silicon), 5XXX series (alloyed with magnesium), 6XXX series (alloyed with magnesium and silicon), 7XXX series (alloyed with zinc), and 8XXX series (alloyed with other elements not covered by other series). Cast alloys are included in the 1xx.x series (minimum 99% aluminum), 2xx.x series (alloyed with copper), 3xx.x series (alloyed with silicon, copper, and / or magnesium), 4x.xx series (alloyed with silicon), 5xx.x series (alloyed with magnesium), 7xx.x series (alloyed with zinc), 8xx.x series (alloyed with tin), and 9xx.s series (alloyed with other elements not covered by other series).

[0037] With regard to the seventh workpiece material category, the workpiece is composed of pure copper or a copper alloy. There are as many as 400 different copper and copper alloy compositions that are loosely grouped into the following categories: copper, high copper alloys, brass, bronze, copper-nickel, copper-nickel-zinc (nickel silver), lead-copper, and special alloys. All groups and categories are considered to be within this metal category. Copper alloys and brasses (where zinc is the primary alloying element) are referenced by UNS numbers X1xxx through C4xxxx and C66400 through C69800. Phosphor bronzes, where tin is the primary alloying element, are referenced by UNS numbers C5xxxx. Aluminum bronzes, where aluminum is the primary alloying element, are referenced by UNS numbers C60600 through C64200. Silicon bronzes, where silicon is the primary alloying element, are referenced by UNS numbers C64700 through C66100. Cupronickel / nickel silver, in which nickel is the major alloying element, is referred to by the UNS numbers C7xxxx.

[0038] Regardless of the particular workpiece material, the workpiece may be formed or fabricated by any method, such as, but not limited to, wrought metal forming, casting, drawing, extrusion, superplastic forming, diffusion bonding, powder metallurgy, sintered products and by-products thereof, welding, explosive bonding, rotational molding, and additive manufacturing.

[0039] The electrolyte solution in which the workpiece and electrodes are immersed in steps 210 and 220 generally comprises any suitable electrolyte solution having a conductivity greater than 0.011649 microsiemens per cm at 0° C. (ASTM D1125-95 1999). For Faraday's law of electrolysis to be valid, the electrolyte solution must be capable of transporting any charge introduced. Pure water, which has a conductivity of 0.011649 microsiemens per cm at 0° C., will not support the transport of an introduced charge unless the driving force (voltage) is too large to bridge the gap from one electrode to the other. Thus, the electrolyte solutions used herein must have a conductivity greater than that of pure water.

[0040] The specific composition of the electrolyte solution is not limited as long as it meets the conductivity requirements previously described. The specific composition of the electrolyte solution may be selected based on, for example, the material composition of the workpiece and / or electrodes. For example, the exact chemical species of the electrolyte may be selected based on the metal ions involved in the electrolysis reaction. The electrolyte solution may be aqueous or non-aqueous.

[0041] Various solutes can be included in the electrolyte composition to adjust the conductivity of the electrolyte solution. Elements and their compounds from alkali metals, alkaline earth metals, transition metals, and post-transition metals form good ionic solutes, as do elements halogens, metalloids, non-reactive metals, and their respective salts, acids, bases, and oxides. In addition, organic compounds and their complexes, such as alcohols, aldehydes, ketones, carboxylic acids, amines, etc., can play a beneficial role in the electrolyte. Suitable organic compounds can be water-soluble or water-insoluble. Surfactants may also be used in the electrolyte composition.

[0042] In some embodiments, the electrolyte is free or substantially free of nitrogen and nitrogen-containing compounds, such as, but not limited to, nitrates. By providing an electrolyte solution that is free or substantially free of nitrogen and nitrogen-containing compounds, the processes described herein can reduce NO x Off-gassing can be avoided. NO x Due to regulatory, environmental, and health and human safety issues associated with off-gas emissions, NO x It is generally desirable to avoid off-gas emissions.

[0043] In step 230, a first mode of operation is initiated, where a first type of current is applied to the electrolyte solution between the conductive metal workpiece and the electrode. Generally speaking, the first type of current is either direct or alternating current. Either type of current can be used in step 230, provided that step 240 uses a type of current that was not used in step 230. The method is generally materially agnostic regardless of whether alternating or direct current is used initially. As will be explained in more detail below, the first type of current applied in step 230 is maintained for a period of time, after which step 240 is performed to terminate the first mode of operation. Terminating the first mode of operation generally involves terminating the application of the first type of current such that no current is applied to the electrolyte between the workpiece and the electrode.

[0044] In step 250, a second mode of operation is initiated, in which a second type of current is applied to the electrolyte solution between the conductive metal workpiece and the electrode. Generally speaking, the second type of current can be either direct or alternating current, so long as it is not the same type of current used in the first mode of operation. As will be explained in more detail below, the second type of current applied in step 250 is maintained for a period of time, after which step 260 is performed to terminate the second mode of operation. Terminating the second mode of operation generally involves terminating the application of the second type of current such that no current is applied to the electrolyte between the workpiece and the electrode.

[0045] For simplicity, the following description describes an embodiment in which a direct current is applied in a first operating mode and an alternating current is applied in a second operating mode, however, as previously noted, the system and method are not limited to this order and in other embodiments, the first operating mode may include application of an alternating current and the second operating mode may include application of a direct current.

[0046] In non-limiting embodiments in which the first type of current applied in step 230 as part of the first operating mode is direct current, the direct current may be applied to the workpiece or electrode at a single polarity, or the direct current may be applied at both negative and positive voltages within a single operating mode.

[0047] In a single polarity embodiment, the applied voltage is not switched between positive and negative while the direct current is applied within a given first operating mode. That said, the particular voltage applied may vary within a positive range or within a negative range during the first operating mode. For example, within the same operating mode, the direct current may be applied for some time at a first constant voltage, as well as for some time at a second constant voltage having the same polarity but different from the first. However, in some embodiments, it is preferred that the voltage applied during the first operating mode is constant and of the same value whenever the direct current is applied. For example, when the first operating mode is first implemented, the applied voltage may be maintained constant at +48V during the first operating mode, or whenever during the first operating mode when the direct current is applied. During the first operating mode, at times, the DC power supply may be interrupted (i.e., the voltage goes to zero), but if the DC power supply is resumed during the first operating mode, the same constant voltage used previously within the first operating mode is used when the direct current is applied again.

[0048] In a bipolar embodiment, a first operating mode may use a first constant voltage, e.g., positive, for a first period of time, and then use a second constant voltage, e.g., negative, for a second period of time during the same first operating mode. For example, a first operating mode may apply a constant +24 VDC for the first 2 seconds of the first operating mode, and then change the voltage to a constant -12 VDC for the subsequent 2 seconds of the first operating mode.

[0049] In some embodiments, the operating voltage for a DC power supply ranges from about -480 VDC to about +480 VDC, including all values ​​therebetween. In some embodiments, a range of +50 VDC to +240 VDC, or -50 VDC to -240 VDC, is used. The applied voltage, in conjunction with the physical attributes of the workpiece and electrodes, along with the electrolyte, produces a resultant current flow or amperage that will be readily understood by one of ordinary skill in the art.

[0050] As previously mentioned, the duration of the constant voltage from the DC power supply can be applied continuously or in two or more intermediate intervals during a given first mode of operation. If intermediate intervals are used, the duration of the intervals can be as short as 1 millisecond in duration. The intermediate intervals can be of constant length or variable, and the intermediate intervals can be applied symmetrically or cyclically. If direct current is applied continuously throughout the first mode of operation, the duration of the first mode of operation can be as short as 1 millisecond in duration.

[0051] When the first operating mode is repeated after the end of the second operating mode, the subsequent first operating mode may use the same operating parameters as the preceding first operating mode, or may use one or more different operating parameters. In an embodiment where the subsequent first operating mode uses the same operating parameters as the preceding first operating mode, both the preceding and subsequent first operating modes may use a constant voltage of +48 VDC for the entire duration of the respective first operating modes. In an embodiment where the subsequent first operating mode uses different operating parameters than the preceding first operating mode, the preceding first operating mode may use a constant voltage of +24 VDC for the entire duration of the preceding first operating mode, while the subsequent first operating mode may use a constant voltage of +48 VDC, where the voltage is applied in two intermediate intervals with a break (i.e., a period during which the voltage remains zero) between the two intervals.

[0052] After the first mode of operation is terminated in step 240, a second mode of operation is initiated in step 250, which in this embodiment uses alternating current. As used herein, alternating current is intended to mean that the slope of the alternating current waveform (voltage versus time) is constantly changing. Thus, step-like voltage changes that typically mimic alternating current are not considered to be included in the meaning of alternating current as used herein, since a step-like waveform includes cases where the slope does not change.

[0053] The shape of the waveform of the alternating current applied in step 250 is generally not limited so long as the above provisions regarding continuous change in slope are met. In some embodiments, the alternating current is applied as a symmetrical sinusoidal waveform with a constant maximum voltage, although other waveform shapes may also be used, such as, but not limited to, compound waves, "camel hump" waves, and other irregular and / or asymmetric wave shapes.

[0054] Regardless of the shape of the waveform, the voltage range of the AC varies within the range of about -480 VAC to about +480 VAC, including all values ​​therebetween. In embodiments where a symmetrical sinusoidal waveform is used, the constant maximum voltage can be greater than 0 VAC to about +480 VAC. The AC used does not need to switch polarity. For example, all values ​​in the AC waveform can be above 0 VAC or below 0 VAC.

[0055] Another parameter of the alternating current that can be controlled is the frequency. In some embodiments, the alternating current has a frequency in the range of about 6 Hz to about 600 MHz. The frequency can be applied symmetrically or can be cycled unevenly.

[0056] The duration of the voltage from the AC power supply can be applied continuously or in two or more intermediate intervals during a given second mode of operation. If intermediate intervals are used, the duration of the intervals can be as short as 1 millisecond in duration. The intermediate intervals can be of constant length or variable, and the intermediate intervals can be applied symmetrically or cyclically. If the alternating current is applied continuously throughout the second mode of operation, the duration of the second mode of operation can be as short as 1 millisecond in duration.

[0057] When the second mode of operation is repeated after the end of the first mode of operation, the subsequent second mode of operation may use the same operating parameters as the preceding second mode of operation, or may use one or more different operating parameters. In an embodiment where the subsequent second mode of operation uses the same operating parameters as the preceding second mode of operation, both the preceding and subsequent second modes of operation may use a symmetrical sinusoidal AC voltage with a constant maximum of +48 VAC at the same frequency throughout the duration of the respective second modes of operation. In an embodiment where the subsequent second mode of operation uses different operating parameters than the preceding second mode of operation, the preceding second mode of operation may use a symmetrical sinusoidal AC voltage with a constant maximum voltage of +48 VAC throughout the duration of the preceding second mode of operation, while the subsequent second mode of operation may use a symmetrical sinusoidal AC voltage with a constant maximum voltage of +24 VAC, where the voltage is applied in two intermediate intervals with a break (i.e., a period during which the voltage remains zero) between the two intervals. The preceding second mode of operation and the subsequent second mode of operation may also vary in one or more of the shape, amplitude, wavelength, and frequency of the waveform.

[0058] While the previous section describes changes in the alternating current between a preceding second mode of operation and a subsequent second mode of operation, it should be understood that one or more of the shape, amplitude, wavelength, and frequency of the waveform of the alternating current may be changed within the second mode of operation. For example, the second mode of operation may use a symmetric sinusoidal waveform during an initial portion of the second mode of operation, but increase or decrease the amplitude of the sinusoidal waveform during the course of the second mode of operation.

[0059] In one particular embodiment, an initial first operating mode uses constant DC at a first voltage during the initial first operating mode, and each subsequent first operating mode uses constant DC at an increasing voltage for each additional first operating mode. For example, an initial first operating mode uses a constant voltage of +3VDC, a next first operating mode uses a constant voltage of +6VDC, a next first operating mode uses a constant voltage of +9VDC, and so on. With the increase in DC voltage during the first operating mode, a corresponding second operating mode using AC during the first operating mode may use a symmetrical sinusoidal waveform with a progressively increasing maximum voltage. For example, an initial second operating mode after an initial first operating mode may use AC using a symmetrical sinusoidal waveform with a maximum voltage of +3VAC, a next second operating mode uses a maximum voltage of +6VAC, a next second operating mode uses a maximum voltage of +9VAC, and so on.

[0060] 3A and 3B, these graphs show various operating schemes that can be used for the methods and systems described herein. FIG. 3A shows an operating scheme in which an initial first operating mode and all subsequent first operating modes use the same operating parameters, and an initial second operating mode and all subsequent second operating modes use the same operating parameters. More specifically, an initial first operating mode 301 and all subsequent first operating modes 301′ and 301″ apply direct current at the same constant voltage during each first operating mode, where each first operating mode has the same duration, while an initial second operating mode 302 and all subsequent second operating modes 302′ and 302″ apply alternating current using a symmetrical sinusoidal waveform with the same maximum voltage, frequency, and wavelength, where each second operating mode is performed for the same duration.

[0061] 3B shows another embodiment of an operating scheme that can be used, where the constant voltage of DC applied in each first operating mode is increased in each subsequent first operating mode, and the maximum voltage of the symmetrical sinusoidal waveform used when applying AC in the second operating mode is increased in each subsequent second operating mode. More specifically, an initial first operating mode 311 applies DC at a first voltage, and a first subsequent first operating mode 311' (and all subsequent first operating modes thereafter) applies DC at a second voltage that is equal to, greater than, or less than the first voltage. The duration of each first operating mode is the same, and DC is applied for the duration of each first operating mode. Meanwhile, the initial second operating mode 312 applies an alternating current using a symmetrical sinusoidal waveform having a first maximum voltage, and the first subsequent second operating mode 312' (and all subsequent second operating modes thereafter) applies an alternating current using a symmetrical sinusoidal waveform having a second maximum voltage that is equal to, exceeds, or is less than the first maximum voltage, while all other operating parameters of the second operating modes (e.g., second operating mode duration, frequency, waveform, etc.) are the same.

[0062] As previously discussed, the methods and systems described herein may be beneficially used to affect the surface of a conductive metal workpiece. The term "affect" as used herein is intentionally broad, as the methods described herein may involve either the deposition of material onto the workpiece or the removal of material from the workpiece. Measurement of this improvement may be performed by a surface profilometer. In some embodiments, a reduction in surface finish measurements from 1 Ra to 500 Ra is achieved. FIG. 4 provides a table relating Ra values ​​to industry established grit values ​​(e.g., used in classifying abrasive papers). With respect to beneficially affecting the surface of a workpiece by removing material from the surface of the workpiece, removal of material from the surface of the workpiece includes (but is not limited to) the use of the systems and methods described herein to perform electrochemical pickling (or functional equivalent) and chemical polishing (or functional equivalent). Measurement of the improvement in the surface of a workpiece when using embodiments of the systems and methods described herein to perform electrochemical pickling and chemical polishing (or functional equivalents) can be made by thickness or gauge measurements with tools such as micrometers or ultrasonic thickness gauges. In some embodiments, precise reductions in gauge of 0.0005 inches to 0.5000 inches or better are achieved.

[0063] In some embodiments, a beneficial effect on surface morphology resulting from the systems and methods described herein is the creation of localized variations in surface morphology. The specific types of localized variations in surface morphology are generally not limited and may include any type of surface morphology difference relative to the remainder of the workpiece. Exemplary non-limiting localized variations in surface morphology that may be created by the systems and methods described herein include the presence of crystals in enclosed areas on the workpiece, and the creation of localized markings identifiable by a change in color (e.g., black lines formed on a particular portion of the workpiece).

[0064] Localized variations in surface morphology, such as those described above, can be beneficial in that they generally indicate the presence of anomalies in the workpiece proximate to the localized variations. Specific anomalies associated with localized variations in surface morphology are generally not limited and can include, for example, changes in surface chemistry or the presence of subsurface defects such as subsurface voids. Identifying these localized variations on the workpiece (which can be treated as "markers") can result in opportunities for subsequent remedial or beneficial processing of the workpiece (e.g., mechanical polishing). As a result, the system 100 described herein can be expanded to include one or more devices that can identify these localized variations in surface morphology and thereby identify opportunities for further processing of the workpiece. Any suitable device for identifying localized variations can be used, such as, for example, an optical scanner.

[0065] Furthermore, it should be understood that the beneficial effects obtained by the methods and systems described herein may not include changes in surface morphology. For example, the beneficial impact obtained may be related to a change in the surface chemistry of the workpiece. For example, when extraneous iron is removed from the surface, passivation of stainless steel occurs and the surface of the metallic species is reinforced with a barrier layer of metal oxide. Although no measurable improvement in surface finish is realized in this case, the change in surface chemistry still provides a benefit to the workpiece. Thus, beneficially affecting the workpiece by a change in surface chemistry may include, for example, removing metallic material, adding oxygen (e.g., by forming an oxide layer), removing hydrogen, preventing or inhibiting hydrogen bonding, or any combination thereof.

[0066] In some embodiments, a beneficial effect on the surface of a conductive metal workpiece resulting from the systems and methods described herein is to load hydrogen at least on the surface of the metal workpiece. In this manner, the metal workpiece can be used for hydrogen storage, which can be beneficial for applications where hydrogen is used as an energy source. When loading hydrogen into a metal workpiece using the methods and systems described herein, the surface and a portion of the interior of the workpiece can be loaded with hydrogen. For example, hydrogen can be stored on the surface of the workpiece and along grain boundaries located within the metal workpiece.

[0067] Although not shown in FIG. 1, other process parameters may be adjusted and / or manipulated as part of the system 100 to improve the performance of the methods described herein. In one example, the thermal activity of the electrolyte may be an important component of molecular activity and therefore may be controlled to affect the ability of the electrolyte to transport charge. In some embodiments, the electrolyte solution used in the system 100 described herein operates within an operating range of about 10° C. to about 100° C. In some embodiments, the processes described herein are carried out at a controlled processing temperature, but the temperature may be controlled (e.g., elevated above room temperature) as a means to accelerate the desired electrochemical reaction. Warming to the system 100 to accelerate the electrochemical reaction may be provided by the heating device 170 previously described. In other embodiments, the processes described herein are carried out while the temperature may be controlled at a reduced processing temperature as a means to reduce the desired electrochemical reaction provided by the cooling device 170 previously defined. Precise control of the heating device 170 thereby allows for precise control of the electrochemical reaction and surface treatment. This precise control of the process temperature and corresponding precise control over the electrochemical reactions thereby allows the systems and processes to operate without the need for, for example, limited loads, expensive chillers, and / or hold times that often necessitate other surface treatment processes such as pickling.

[0068] Additionally, other externally applied physical forces may be beneficial to the overall performance of the systems and methods described herein. As previously mentioned, the mixing rate of the electrolyte can have a significant effect on the thin barrier layer adjacent to the electrodes. Thus, in some embodiments of the system 100 described herein, an additional step is performed to mix the electrolyte during the process described above. Mixing may be performed by any suitable means, for example, by either physical or thermal mixing. Pumps, mixers, spargers, devices configured to move the workpiece and / or electrodes, specific fluid delivery methods, etc., in combination with heat transfer mechanisms and chemical reactions, both exothermic and endothermic, may all have their own beneficial impact on the outcome of the electrolysis reaction.

[0069] In some embodiments, one or more of any of the various operating parameters previously described with respect to the operation of the system 100 can be controlled, adjusted, and / or manipulated in such a manner as to control the barrier layer formed on the workpiece and / or electrode. The operating parameters of the system 100 that can be controlled for the purpose of controlling the barrier layer can relate to the operating parameters of chemical, mechanical, electrical, magnetic, and / or molecular excitations. Control of the barrier layer can relate, for example, to control of the thickness of the barrier layer, control of the chemical composition of the barrier layer, and / or any other characteristic of the barrier layer. Controlling the operating parameters of the system 100 in such a manner to control the barrier layer beneficially allows for control of the availability or lack of availability of dissociated ionic species derived from the components of the electrolyte. This, in turn, allows for precise control of the chemical reactions involved in the electrochemical processes described herein, which in turn allows for precise control over the manner in which the surface of the workpiece is beneficially affected. This can be in stark contrast to other previously known methods for modifying the surface of a workpiece, such as pickling, which are notoriously difficult to control due, for example, to exothermic reactions that occur as part of the pickling process, causing the reaction to proceed at a gradually rapid and uncontrolled rate.

[0070] In some embodiments, the system 100 further includes one or more pieces of equipment configured to automatically monitor, analyze, and / or adjust one or more operating parameters that can be used to control the barrier layer, which allow for control of the equipment in a manner that beneficially affects the workpiece. The equipment can be programmed with computer-executed instructions, thereby allowing for automatic control of the systems and processes described herein to obtain a desired result for the workpiece. In other words, no human intervention may be required when the operating parameters are automatically monitored, analyzed, and adjusted by additional equipment to obtain a desired result for the workpiece. Such equipment generally operates based on known relationships between the various operating parameters and their associated effects on the barrier layer, further helping to provide a highly repeatable process that achieves the same or nearly the same results for each individual workpiece processed using the techniques described herein.

[0071] Given the various ways in which the operation of the system 100 is precisely controlled and the method 200 described herein is precisely performed, the techniques described herein are highly repeatable: a single set of precise operating parameters can be used to repeatedly and reliably obtain the same or substantially the same results for the same workpiece, electrode, and / or electrolyte combination.

[0072] One advantage provided by the systems and methods described herein is the ability to tightly control the impact on the surface for extreme material types. For example, aluminum is generally considered to be a metallic material that is extremely easy to corrode, making it difficult to precisely control the material removal (e.g., removal of very small amounts of material). However, using the systems and methods described herein, it is possible to gently polish aluminum. Similarly, niobium is generally considered to be a metallic material that is extremely difficult to corrode, making it difficult to remove relatively large amounts of material. However, using the systems and methods described herein, it is possible to aggressively remove niobium.

[0073] Experimental Results

[0074] In some of the embodiments described below, reference is made to a color chart documented by the Massachusetts Institute of Technology (MIT). This color chart presents the interference colors exhibited by reactive metals with relatively thin surface oxide layers that form on the metal's surface as a function of dissociation voltage. When the surface oxide layers are relatively thin (30-150 nm), they block light and create the perception of color to the human eye. These interference colors are a function of the oxide thickness. This process is typically carried out by DC electrolysis and results when a metal is anodically charged in a conducting electrolyte. When water dissociates, nascent oxygen binds to the anodic metal electrode. These oxides are highly resistive to electrical current, resulting in the need to increase the circuit potential to increase the oxide thickness.

[0075] Workpiece material category 1 – reactive metals

[0076] Experiment 1

[0077] In an aqueous electrolyte composed of citric acid (15 g / L) and ammonium bifluoride (8 g / L) at 66° C., the niobium coupons were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 24 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 24 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material achieved a gauge loss of 0.074 inches per minute and a moderate improvement in surface finish of 5%.

[0078] Experiment 2

[0079] In an aqueous electrolyte composed of citric acid (30 g / L) and ammonium bifluoride (10 g / L) at 66° C., a test specimen of nuclear grade zirconium alloy Zr-2.5Nb (UNS R60901) was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 24 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 24 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material achieved a gauge loss of 0.056 inches per minute and a surface finish loss of 24%.

[0080] Experiment 3

[0081] In an aqueous electrolyte composed of 150 g / l magnesium chloride at 40° C., commercially pure titanium (Ti-CP, UNS R50400) specimens were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing, and 6 volts in each of the third, fourth, and fifth pairings, until reaching 24 volts in both AC and DC modes in the final pairing. The total operating time was 2.5 minutes. This resulted in oxide growth equivalent to the thickness indicated by the MIT chart for a conventional 50 VDC process. OSHA regulations at 29 CFR 1910.303(g)(2)(i) require protection of exposed electrical equipment at or below 50 volts, regardless of whether it is generated by AC or DC methods. Providing traditional results at low operating voltages provides significant operational advantages to workers exposed to those operating conditions.

[0082] Experiment 4

[0083] In an aqueous electrolyte composed of 50 g / L sodium bisulfate, 150 g / L magnesium chloride at 50° C., aerospace grade titanium (Ti-6Al-4V, UNS R56400) specimens were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until reaching 24 volts in both AC and DC modes in the final pairing. The total operating time was 2.5 minutes. This resulted in oxide growth equivalent to the thickness shown by the MIT chart of a conventional 115 VDC process, resulting in a nearly 5-fold reduction in operating voltage.

[0084] Experiment 5

[0085] In an aqueous electrolyte consisting of 30 g / L citric acid, 10 g / L ammonium bifluoride at 45° C., aerospace grade titanium (Ti-6Al-4V, UNS R56400) specimens covered with mill scale were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 5 Hz AC at 24 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 24 volts for 15 seconds, repeating these two operating modes 360 times for a total operating time of 180 minutes. Titanium mill scale is a heavy oxide that exhibits similar properties to ceramics in hardness and corrosion resistance. Conventional processing requires abrasive media blasting or other machine tools to crack the oxide so that hydrofluoric acid can impregnate it, and to remove the chemically inert material from the metal surface or undercut it to remove it completely. Without affecting the scale prior to treatment, once it has been completely removed, the underlying material is subjected to selective and inconsistent removal, resulting in an irregular removal of the scale resulting in a rough and sometimes pitted surface. The specimens in this trial were not subjected to any pretreatment. The scaly material was subjected directly to electrochemical manipulation and was oxide-free and physically intact at the end of the cycle. Uniformly smooth surface. Achieving this result by electrochemical methods alone is of remarkable importance.

[0086] Additional data relating to the above experiments and additional experiments performed on reactive metals are set forth in the tables presented in Figures 5A and 5B.

[0087] Workpiece material category 2 – High temperature / high strength metals

[0088] Test 6

[0089] In an aqueous electrolyte composed of citric acid (30 g / L) and ammonium bifluoride (10 g / L) at 66° C., Nitinol nickel-titanium alloy (Ni-45Ti, UNS N01555) specimens were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 24 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 24 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material achieved a 12% improvement in surface finish while undergoing a gauge loss of 0.037 inches per hour.

[0090] Test 7

[0091] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of austenitic alloy C22 (UNS N06022, Ni-22Cr-13Mo-3Fe-3W) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until reaching 24 volts in both AC and DC modes in the final pairing. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was oxide free and smooth, exhibiting a 13% loss in surface finish while undergoing a gauge loss of 0.019 inches per hour.

[0092] Test 8

[0093] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of nickel alloy Nimonic Alloy 90 (UNS N07090, Ni-20Cr-16Co-3Ti-2Al) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was smooth and exhibited a 19% loss in surface finish while undergoing a gauge loss of 0.019 inches per hour.

[0094] Additional data relating to the above experiments and additional experiments performed on high temperature / high strength alloys are set forth in the tables presented in Figures 6A-6E.

[0095] Workpiece material category 3 – Austenitic stainless steels

[0096] Test 9

[0097] In an aqueous electrolyte composed of sodium bisulfate (50 g / L) and magnesium chloride (150 g / L) at 40° C., heat-treated specimens of austenitic creep-resistant steel alloy X20CrMoC11-1 (DIN 1.4922, Fe-11Cr-1Mo-1Ni-1Mn) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme of this experiment was to provide 60 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material experienced a 2% reduction in surface finish while undergoing a gauge loss of 0.034 inches per hour.

[0098] Test 10

[0099] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of austenitic stainless steel alloy Nitronic 50 (XM-19, UNS S20910, Fe-21Cr-13Ni-5Mn-3Mo-0.3N-0.2Nb) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme of this experiment was to provide 600 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was free of heat treated oxides, bright and smooth, exhibiting a 23% loss in surface finish and a minimal gauge loss of 0.0024 inches per hour.

[0100] Test 11

[0101] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of austenitic stainless steel alloy 316L (UNS S31603, Fe-18Cr-15Ni-3Mo-2Mn) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until reaching 24 volts in both AC and DC modes in the final pairing. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was free of heat treated oxides, bright and smooth, exhibiting a 26% loss in surface finish and a minimal gauge loss of 0.0048 inches per hour.

[0102] Test 12

[0103] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of borate alloyed austenitic 304 stainless steel (UNS S30463, Fe-19Cr-13Ni-2B) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was free of heat treated oxides, bright and smooth, exhibiting a 5% loss in surface finish and a minimum gauge loss of 0.0144 inches per hour.

[0104] Test 13

[0105] In an aqueous electrolyte composed of sodium bisulfate (50 g / L) and magnesium chloride (150 g / L) at 40° C., heat treated specimens of austenitic 303 stainless steel (UNS S30300, Fe-18Cr-9Ni-1.8Mn-0.25S) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material achieved a moderate gauge reduction of 0.043 inches per hour.

[0106] Additional data relating to the above experiments and additional experiments performed on austenitic stainless steels is set forth in the tables presented in FIGS. 7A-7F.

[0107] Workpiece material category 4 – Martensitic stainless steels

[0108] Test 14

[0109] In an aqueous electrolyte consisting of 67% by volume phosphoric acid (85% by weight), 33% by volume sulfuric acid (50% by weight), 5% by weight HO, and 0.1 ml / L lauric aldehyde at 50° C., a 440C martensitic stainless steel (UNS S44004, Fe-17Cr-0.75Mo-0.5Mn-0.5Ni-0.5Si) specimen was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 600 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. Total run time was 2.5 minutes. The material experienced negligible change in surface finish of 3μ inch while undergoing a minimal gauge loss of 0.008 inch per hour.

[0110] Additional data relating to the above experiments and additional experiments performed on martensitic stainless steels is set forth in the table presented in FIG.

[0111] Workpiece material category 5 – Ferritic stainless steel, carbon steel, or alloy steel

[0112] Test 15

[0113] In an aqueous electrolyte composed of 5.0 wt.% sodium hydroxide and 2.4 wt.% ammonium hydroxide at 21° C., a specimen of 430 ferritic stainless steel (UNS S43000, Fe-17Cr-0.7Mn-0.60Si) was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 50 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 26 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. The material experienced a gauge loss of 0.045 inches per hour and became moderately roughened as indicated by a loss in surface finish of 17%.

[0114] Test 16

[0115] In an aqueous electrolyte consisting of 53 wt% sulfuric acid, 28 wt% trisodium phosphate, 18 wt% water, and 1 wt% barium sulfate, and 0.1 ml / L 2-butoxyethanol / propylene glycol at 32°C, a 430 ferritic stainless steel (UNS S43000, Fe-17Cr-0.7Mn-0.60Si) specimen was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 5 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 10 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. The material exhibited a rapid gauge loss of 0.295 inches per hour and a 2μ inch R in surface finish. a showed an increase in

[0116] Test 17

[0117] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated specimens of low carbon steel alloy 15CDV6 (DIN 1.7734, Fe-1.4Cr-0.9Mo-0.2V-6Al-2Sn) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme of this experiment was to provide 600 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until reaching 24 volts in both AC and DC modes in the final pairing. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was bright and smooth, with a 26% reduction in surface finish observed while undergoing a gauge loss of 0.024 inches per hour.

[0118] Test 18

[0119] In an aqueous electrolyte consisting of 50 ml / L fluoroboric acid (50 wt%) at 40° C., heat treated alloy steel specimens of AISI M2 molybdenum high speed tool steel (UNS T11302, Fe-6W-5Mo-2V-1C-0.4Cr-0.3Ni) were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme of this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times, increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material was free of heat treatment oxide, bright and smooth, and exhibited a 13% loss in surface finish while undergoing a gauge loss of 0.060 inches per hour.

[0120] Test 19

[0121] Heat treated alloy steel specimens of AISI M2 molybdenum high speed tool steel (UNS T11302, Fe-6W-5Mo-2V-1C-0.4Cr-0.3Ni) in an aqueous electrolyte composed of sodium bisulfate (50 g / L) and magnesium chloride (150 g / L) at 40° C. were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 6 Hz AC at 3 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 3 volts for 15 seconds, repeating these two operating modes five times and increasing the voltage in both AC and DC modes by 3 volts in the second pairing and 6 volts in each of the third, fourth, and fifth pairings until the final pairing reached 24 volts in both AC and DC modes. The total operating time was 2.5 minutes. Upon completion of the cycle, the material contained no heat treatment oxide and experienced a 25% loss in surface finish while undergoing a gauge loss of 0.007 inches per hour.

[0122] Test 20

[0123] In an aqueous electrolyte consisting of 53 wt.% sulfuric acid, 28 wt.% trisodium phosphate, 18 wt.% water, and 1 wt.% barium sulfate, and 0.1 ml / L 2-butoxyethanol / propylene glycol at 82° C., a 1020 carbon steel (UNS G10200, Fe-0.2C-0.5Mn) specimen was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 2 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 1.2 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material experienced rapid material removal of 0.342 inches per hour as well as being polished, while simultaneously undergoing a 28% reduction in surface finish.

[0124] Additional data relating to the above experiments and additional experiments performed on ferritic metals is set forth in the tables presented in Figures 9A-9D.

[0125] Workpiece material category 6 – Aluminum and aluminum alloys

[0126] Test 21

[0127] In an aqueous electrolyte consisting of 53 wt.% sulfuric acid, 28 wt.% trisodium phosphate, 18 wt.% water, and 1 wt.% barium sulfate, and 0.1 ml / L 2-butoxyethanol / propylene glycol at 36° C., a specimen of precipitation hardened aluminum alloy 6061 (UNS A96061, Al-1Mn-0.6Si-0.28Cu-0.2Cr) was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 10 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 12 volts for 15 seconds, and repeat these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material exhibited a bright, reflective surface and suffered a corresponding 25% reduction in surface finish and a gate loss of 0.187 inches per hour. This polished surface is desirable for many applications, and the potentially explosive chemistry of perchloric acid has traditionally been practiced in ventilation systems or where it is allowed to crystallize from solution due to poor industrial housekeeping. The bimodal power supply is believed to act on and rejuvenate the Beilby layer adjacent to the workpiece to favorably affect the surface of the material.

[0128] Test 22

[0129] In an aqueous electrolyte composed of 5.0 wt. % sodium hydroxide and 2.4 wt. % ammonium hydroxide at 24° C., a specimen of non-heat treated aluminum alloy 5052 (UNS A95052, Al-2.5Mn-0.25Cr) was subjected to a bimodal A / C and D / C power supply configured according to an embodiment described herein. The operating scheme for this experiment was to provide 60 Hz AC at 50 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by DC at 26 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Throughout the cycle, the DC amperage decreased with time, while the amperage resulting from the AC supply increased, as the electrically resistive aluminum oxide grew. Upon completion of the cycle, the material showed a significant growth in aluminum oxide film thickness equal to 0.141 inches per hour and a corresponding increase in surface finish of 109%. The bimodal power supply is believed to enable rapid growth of film thickness with DC current, while AC current reactivates or "peels" the resistive layer of the film in the electrolyte, reviving the system for further growth.

[0130] Additional data relating to the above experiments and additional experiments performed on aluminum are set forth in the table presented in FIG.

[0131] Workpiece material category 7 – Copper and copper alloys

[0132] Test 23

[0133] In an aqueous electrolyte consisting of 53 wt.% sulfuric acid, 28 wt.% trisodium phosphate, 18 wt.% water, and 1 wt.% barium sulfate, and 0.1 ml / L 2-butoxyethanol / propylene glycol at 24° C., an AMS 4535 beryllium copper (UNS C17200, Cu-1.9Be-0.2Co) specimen was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 5 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 8.5 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material achieved a significant removal rate of 0.283 inches per hour, making this alloy important for its corrosion resistance, especially in downhole applications where resistance to sulfur compounds is important.

[0134] Test 24

[0135] In an aqueous electrolyte composed of 5.0 wt.% sodium hydroxide and 2.4 wt.% ammonium hydroxide at 21° C., AMS 4535 beryllium copper (UNS C17200, Cu-1.9Be-0.2Co) specimens were subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 50 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 26 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material achieved a significant removal rate of 0.084 inches per hour, making this alloy important for its corrosion resistance, especially in downhole applications where resistance to sulfur compounds is important.

[0136] Test 25

[0137] In an aqueous electrolyte composed of 5.0 wt. % sodium hydroxide and 2.4 wt. % ammonium hydroxide at 18° C., a specimen of 360 free-cutting brass (UNS C36000Cu-35.5Zn-3Pb-0.35Fe) was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 60 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by 15 seconds of direct current at 60 volts, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material developed a uniform black appearance, which was attributed to a finely divided surface that trapped light and prevented its reflection, giving the perception of a black coating regardless of the measured change in surface finish of 2 μ-inches of Ra.

[0138] Test 26

[0139] In an aqueous electrolyte consisting of 53 wt.% sulfuric acid, 28 wt.% trisodium phosphate, 18 wt.% water, and 1 wt.% barium sulfate, and 0.1 ml / L 2-butoxyethanol / propylene glycol at 28°C, a specimen of bearing bronze (UNS C93200, Cu-10Pb-10Sn) was subjected to a bimodal A / C and D / C power supply configured according to embodiments described herein. The operating scheme for this experiment was to provide 60 Hz alternating current at 50 volts (maximum voltage using a symmetrical sinusoidal waveform) for 15 seconds, followed by direct current at 26 volts for 15 seconds, repeating these two operating modes five times for a total operating time of 2.5 minutes. Upon completion of the cycle, the material developed a uniform black appearance, which was attributed to a finely divided surface that trapped light and prevented its reflection, giving the perception of a black coating regardless of the measured Ra of the 15 μ-inch surface finish.

[0140] Additional data relating to the above experiments and additional experiments performed on copper are set forth in the table presented in FIG.

[0141] From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

[0142] Although the present technology is described in language that is limited to certain structures and materials, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and materials described. Rather, certain aspects are described as forms of practicing the claimed invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

[0143] Unless expressly stated otherwise, all numerical values ​​or expressions used in this specification (except in the claims), such as those expressing dimensions, physical properties, and the like, are understood to be modified in all instances by the term "about." At the very least, and not as an attempt to limit the application to the scope of the claims, each numerical parameter recited in this specification or claims that is modified by the term "about" should be construed in light of at least the significant digits of the recited value by applying rounding techniques. Moreover, all ranges disclosed herein should be understood to encompass and provide support for the claims reciting any subranges or individual values ​​contained therein. For example, a stated range of 1 to 10 should be considered to include and provide support for a claim reciting any subrange or individual value between a minimum value of 1 and a maximum value of 10 (inclusive), i.e., any subrange beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, etc.), or any value between 1 and 10 (e.g., 3, 5.8, 9.9994, etc.).

Claims

1. A bimodal method for affecting the surface of a conductive metal workpiece, Immerse at least the surface of the conductive metal workpiece in an electrolyte solution; Immersing at least the surface of the electrode in the electrolyte solution; Initiating a first operating mode which includes either applying direct current to the electrolyte solution between the conductive metal workpiece and the electrode, or applying alternating current to the electrolyte solution between the conductive metal workpiece and the electrode; To terminate the first operating mode; Initiating a second operating mode, which is different from the first operating mode, which includes either applying alternating current to the electrolyte solution between the conductive metal workpiece and the electrode, or applying direct current to the electrolyte solution between the conductive metal workpiece and the electrode; To terminate the second operating mode described above Including; The conductive metal workpiece is A material selected from the first group, including pure Ti, Zr, Nb, Hf, Ta, or V, or Ti-based, Zr-based, Nb-based, Hf-based, Ta-based, or V-based alloys. A material selected from a second group, including pure Ni, Ni-based alloys, Co-based alloys, or titanium aluminide. Materials selected from a third group, including austenitic stainless steel. Materials selected from a fourth group, including martensitic stainless steel. A material selected from a fifth group, including ferritic stainless steel, carbon steel, or alloy steel. A material selected from the sixth group, including pure aluminum or aluminum alloys, A material selected from the seventh group, including pure copper or copper alloys. Includes one of the following: A bimodal approach.

2. The bimodal method according to claim 1, wherein the steps of starting the first operating mode, ending the first operating mode, starting the second operating mode, and ending the second operating mode are repeated two or more times in succession.

3. The first iteration of the steps of starting the first operating mode, ending the first operating mode, starting the second operating mode, and ending the second operating mode is performed using a first value for the DC voltage and a first value for the maximum value of the AC voltage; Subsequent iterations of the steps of starting the first operating mode, ending the first operating mode, starting the second operating mode, and ending the second operating mode are performed using a second value for the DC voltage and a second value for the maximum value of the AC voltage; The second value for a constant DC voltage is different from the first value for a constant DC voltage, and the second value for a constant maximum AC voltage is different from the first value for a constant maximum AC voltage. The bimodal method according to claim 1.

4. The bimodal method according to claim 1, wherein applying the DC current to the electrolyte solution between the conductive metal workpiece and the electrode includes applying the DC current from the conductive metal workpiece to the electrode.

5. The bimodal method according to claim 1, wherein applying the DC current to the electrolyte solution between the conductive metal workpiece and the electrode includes applying the DC current from the electrode to the conductive metal workpiece.

6. The bimodal method according to claim 1, wherein the distance between the electrode and the conductive metal workpiece is greater than 0.003 inches.

7. The bimodal method according to claim 1, which is performed to deposit a material on the surface of the conductive metal workpiece.

8. The bimodal method according to claim 1, which is performed to remove material from the surface of the conductive metal workpiece.

9. This is carried out to change the interfacial chemistry of the surface of the conductive metal workpiece, Changing the interfacial chemistry of the surface of the conductive metal workpiece is This includes removing the metallic material, adding an oxide layer, or both. This includes removing hydrogen, preventing or inhibiting hydrogen bonding, or both, or filling at least the surface of the conductive metal workpiece with hydrogen. The bimodal method according to claim 1.

10. A system configured to affect the surface of a conductive metal workpiece, Electrolyte solution tank and; A conductive metal workpiece, wherein at least one surface thereof is immersed in the electrolyte solution bath; An electrode, wherein at least one of its surfaces is immersed in the electrolyte solution bath; A DC power supply device wherein its first end is connected to the conductive metal workpiece and its second end is connected to the electrode; An AC power supply device wherein its first end is connected to the conductive metal workpiece and its second end is connected to the electrode; Equipped with, In the first operating mode, the DC power supply is configured to apply only direct current to the electrolyte solution between the conductive metal workpiece and the electrode, or the AC power supply is configured to apply only alternating current to the electrolyte solution between the conductive metal workpiece and the electrode. In the second operating mode, the AC power supply is configured to apply only alternating current to the electrolyte solution between the conductive metal workpiece and the electrode, or the DC power supply is configured to apply only direct current to the electrolyte solution between the conductive metal workpiece and the electrode; The first operating mode is different from the second operating mode; The system is configured to repeat the first operating mode and the second operating mode; and The conductive metal workpiece is A material selected from the first group, including pure Ti, Zr, Nb, Hf, Ta, or V, or Ti-based, Zr-based, Nb-based, Hf-based, Ta-based, or V-based alloys. A material selected from a second group, including pure Ni, Ni-based alloys, Co-based alloys, or titanium aluminide. Materials selected from a third group, including austenitic stainless steel. Materials selected from a fourth group, including martensitic stainless steel. A material selected from a fifth group, including ferritic stainless steel, carbon steel, or alloy steel. A material selected from the sixth group, including pure aluminum or aluminum alloys, A material selected from the seventh group, including pure copper or copper alloys. Includes one of the following: system.

11. Monitoring one or more of the operating parameters of the above method; Analyzing the one or more operating parameters in order to determine whether adjustment to the one or more operating parameters is necessary to change the characteristics of the barrier layer formed on the workpiece; If it is determined that adjustment is necessary, the system automatically adjusts one or more of the operating parameters in order to change the characteristics of the barrier layer. The bimodal method according to claim 1, further comprising:

12. The bimodal method according to claim 1, wherein the electrolyte solution is free of or substantially free of nitrogen and nitrogen-containing compounds.

13. A control system for operating parameters, Monitor one or more operating parameters of the aforementioned system; In order to determine whether adjustment to one or more of the operating parameters is necessary to change the characteristics of the barrier layer formed on the workpiece, the one or more operating parameters are analyzed; If it is determined that adjustment is necessary, the system automatically adjusts one or more of the operating parameters to change the characteristics of the barrier layer. A control system for operating parameters configured as follows: The system according to claim 10, further comprising:

14. The system according to claim 10, wherein the distance between the electrode and the conductive metal workpiece is greater than 0.003 inches.

Images