Erosion-resistant coatings applied by variable bias cathodic arc deposition.

Abstract

The cathodic arc coating system includes at least one alternating layer of titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN) disposed on a substrate, and at least one alternating layer of titanium vanadium chromium nitride (TiVCrN) and titanium silicon vanadium nitride (TiSiVCrN) disposed on the substrate. The cathodic arc process includes a sub-hertz variable bias that forms at least one alternating layer of titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN) disposed on the substrate, and at least one alternating layer of titanium vanadium chromium nitride (TiVCrN) and titanium silicon vanadium nitride (TiSiVCrN) disposed on the substrate.

Description

[Technical Field]

[0001] The present disclosure relates generally to coatings, and more particularly to coatings applied by sub-hertz variable bias ion plasma deposition. [Background technology]

[0002] Solid particle erosion of steam turbine components limits a power generation operator's ability to run active loads after an outage without risking premature failure, thus increasing the levelized cost of energy.

[0003] Two types of coatings have been proposed to mitigate solid particle erosion. The first is a thermally sprayed CrC-NiCr coating known as DiamondTuff®, which has a durable service record but significantly reduces high-pressure steam turbine efficiency. This loss of aerodynamic efficiency can be attributed primarily to the thickness of the thermally sprayed coating (6-10 mils).

[0004] The second coating is TiN deposited by cathodic arc. Cathodic arc TiN coatings can be less than about 0.5 mil thick and therefore do not result in significant aerodynamic efficiency loss. However, they may not be durable enough to prevent damage to turbine blades during planned outages. Simply increasing the thickness of the cathodic arc TiN coating can result in spalling due to residual stresses.

[0005] It is often beneficial to incorporate nanoscale (1-100 nm) layers into the microstructure of cathodic arc coatings, however, the methods available today for this require multiple cathodes and planetary sample rotation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2013 / 0302596 Summary of the Invention

[0007] All aspects, examples, and features described below can be combined in any technically possible manner.

[0008] One aspect of the present disclosure provides a cathodic arc coating system, the coating system comprising alternating layers of titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride disposed on a substrate.

[0009] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers have a thickness in the range of about 1 nanometer (nm) to about 100 nanometers (nm).

[0010] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers have a thickness in the range of about 5 nanometers (nm) to about 100 nanometers (nm).

[0011] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers have a thickness of about 10 nanometers (nm).

[0012] Another aspect of the present disclosure includes any of the preceding aspects, wherein the alternating layers are deposited on the substrate by a sub-hertz variable bias cathodic arc.

[0013] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the alternating layers are deposited on the substrate by a sub-hertz variable bias cathodic arc, the sub-hertz variable bias varying with time as an approximately sinusoidal wave, the approximately sinusoidal wave having a frequency in the range of 0.1 hertz (Hz) to about 1 Hz.

[0014] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers are disposed on the substrate with a sub-hertz variable bias, the sub-hertz variable bias including a modified variable bias waveform having a voltage bias to control the incorporation of vanadium (V), silicon (Si), and / or chromium (Cr).

[0015] Another aspect of the present disclosure includes any of the preceding aspects, wherein the cathodic arc system includes a chamber and a consumable cathode within the chamber, a substrate is disposed in communication with the chamber and the consumable cathode, the substrate acting as an anode; a sub-hertz variable bias generates an electric arc on the cathode, the arc crosses the cathode, the arc interacts with the consumable cathode to produce energetic metal ions, the energetic metal ions are ejected from the consumable cathode, and the energetic ions are accelerated to the substrate.

[0016] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the substrate is provided with a negative charge.

[0017] Another aspect of the present disclosure includes any of the preceding aspects, wherein the chamber includes nitrogen (N) gas therein.

[0018] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the cathode includes titanium (Ti), vanadium (V), silicon (Si), and sometimes chromium (Cr).

[0019] One aspect of the present disclosure provides a sub-hertz variable bias cathodic arc process, the cathodic process including depositing a coating on a substrate having alternating layers of titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN) on the substrate.

[0020] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers have a thickness in the range of about 1 nanometer (nm) to about 100 nanometers (nm).

[0021] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the alternating layers have a thickness of about 10 nanometers (nm).

[0022] Another aspect of the present disclosure includes any of the preceding aspects, wherein the step of disposing alternating layers includes depositing by sub-hertz variable bias cathodic arc.

[0023] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the sub-hertz variable bias varies over time as an approximately sine wave, the approximately sine wave having a frequency in the range of 0.1 hertz (Hz) to about 1 Hz.

[0024] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the sub-hertz variable bias varies periodically with time, and wherein one or more periodic features of the waveform are represented by a frequency within a range of 0.1 hertz (Hz) to about 1 Hz.

[0025] Another aspect of the present disclosure includes any of the aforementioned aspects, wherein the sub-hertz variable bias includes a modified variable bias waveform having a maximum voltage bias modified to control Si content.

[0026] Another aspect of the present disclosure includes any of the preceding aspects, wherein the cathodic arc process includes the steps of: disposing a consumable cathode in a chamber; disposing a substrate in communication with the chamber, where the chamber functions as an anode and the substrate functions as an anode; disposing a reactive gas in the chamber; applying a sub-hertz variable bias to the cathode; generating an electric arc on the cathode by applying the sub-hertz variable bias to the cathode, where the arc crosses a face of the cathode; generating energetic metal ions by the arc interacting with the consumable cathode; ejecting the energetic metal ions from the face of the consumable cathode; and accelerating the energetic ions to the substrate.

[0027] Another aspect of the present disclosure includes any of the preceding aspects, wherein applying the sub-hertz variable bias includes applying the sub-hertz variable bias at a first frequency, wherein emitted energetic metal ions from the consumable cathode pass through the reactant gas at a first velocity, unreacting with at least one of nitrogen and oxygen, and depositing the emitted energetic metal ions on the substrate; and applying the sub-hertz variable bias at a second frequency, wherein the emitted energetic metal ions pass through the reactant gas at a second velocity within the chamber, wherein at the second velocity, the emitted energetic metal ions are allowed to chemically react with nitrogen to form reaction products, and depositing the reaction products on the substrate.

[0028] Another aspect of the present disclosure includes any of the preceding aspects, wherein the substrate is provided with a negative charge relative to the consumable cathode.

[0029] Another embodiment of the present disclosure includes any of the preceding embodiments, wherein the chamber comprises nitrogen (N) and the consumable cathode comprises titanium (Ti), vanadium (V), silicon (Si), and sometimes chromium (Cr).

[0030] Two or more aspects described in this disclosure, including those described in this Summary section, may be combined to form an embodiment not specifically described herein.

[0031] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description and drawings, and from the claims.

[0032] These and other features of the present disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure, taken in conjunction with the accompanying drawings which illustrate various embodiments of the present disclosure. [Brief explanation of the drawings]

[0033] [Figure 1]FIG. 1 is a schematic diagram of a variable bias cathodic arc device according to an embodiment of the present disclosure. [Figure 2] 1 is a flow chart for applying a layer to a substrate from a variable bias cathodic arc device according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a side view of a coated layered substrate structure applied by a variable bias cathodic arc device and process according to an embodiment of the present disclosure. [Figure 4] 1 is a photomicrograph of the microstructure of a coated layered substrate structure according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0034] It should be noted that the drawings of the present disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure and therefore should not be considered limiting of the scope of the disclosure. In the drawings, like numbers represent like elements between the drawings.

[0035] As an initial matter, in order to clearly explain the subject matter of this disclosure, it becomes necessary to select certain terminology when describing it with reference to relevant machine components within turbomachinery, including, but not limited to, steam turbines, which may include low-, intermediate-, and high-pressure steam turbines. Wherever possible, common industry terminology is used and utilized consistent with its accepted meaning. Unless otherwise noted, such terminology should be given a broad interpretation consistent with the context of this application and the appended claims. Those skilled in the art will recognize that in many cases, a particular component may be referred to using several different or overlapping terms. What may be described herein as a single component may include and be referred to in other contexts as consisting of multiple components. Alternatively, what may be described herein as comprising multiple components may be referred to elsewhere as a single component.

[0036] Additionally, as noted below, certain descriptive terms may be used conventionally herein: the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another, but are not intended to denote the location or importance of the individual components.

[0037] The terminology used herein is merely for the purpose of describing particular embodiments and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural unless expressly stated otherwise. It will be further understood that the terms "comprise" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or sets thereof. "Optional" or "optionally" means that a subsequently-stated event or circumstance may or may not occur, or that a subsequently-stated component or element may or may not be present, and the description is meant to include instances in which the event occurs or component is present as well as instances in which it does not occur or is not present.

[0038] When an element or layer is referred to as "on," "engaged," "connected," or "coupled" to another element or layer, it can be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. Conversely, when an element is referred to as "directly on," "directly engaged," "directly connected," or "directly coupled" to another element or layer, there may not be intervening elements or layers. Other terms used to describe relationships between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent to" versus "directly adjacent to," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] Solid particle erosion of turbomachinery components, such as, but not limited to, steam turbine components, can limit the lifespan of the turbomachinery components. Solid particle erosion can also reduce the ability of turbomachinery operators to attempt aggressive loading without risking premature damage to the turbomachinery components. Aggressive load shedding, which may be required to meet power demands and prevent blackouts, rotating load shedding, or steady load shedding, increases electricity costs for all users.

[0040] As shown, a cathodic arc titanium silicon vanadium nitride (TiSiVN) or titanium silicon vanadium chromium nitride (TiSiVCrN) coated layered substrate structure 100 (FIG. 3), as embodied by the present disclosure, provides a very thin, smooth erosion-resistant coating 120 on the substrate 6 both before and after use in a steam turbine that can cause oxidation. Specifically, the cathodic arc TiSiVN or TiSiVCrN coated layered substrate structure 100 can be up to approximately 400% more durable after steam erosion testing than a two-component (CrC-NiCr) conventional erosion-resistant coating, such as DiamondTuff®, despite the fact that these conventional coatings are much thicker (deposited at thicknesses of approximately 6 to 10 mils). The cathodic arc TiSiVN coating system 100 includes an erosion-resistant coating 120 that is approximately 10 to 20 times thinner and approximately 75 to 95% lighter than DiamondTuff®. Even when applied using essentially the same hardware as a conventional cathodic arc process for titanium nitride (TiN), a layered substrate structure 100 coated with cathodic arc TiSiVN deposited by sub-hertz variable bias cathodic arc according to the present disclosure has up to about 24 times greater erosion resistance as deposited and about 14 times greater erosion resistance after vaporization compared to conventional cathodic arc TiN.

[0041] These properties of the cathodic arc TiSiVN or TiSiVCrN coated layered substrate structure 100 (FIG. 3) can be achieved through a combination of process parameters for cathodic arc deposition, including providing a sub-hertz variable bias and depositing silicon (Si), vanadium (V), and optionally chromium (Cr) onto the TiN in a consumable cathode. High nanohardness phases, low oxidation rates, and tailored residual stresses can be produced in the cathodic arc TiSiVN coating system 10 (FIG. 1) and process 200 (FIG. 2) through this microstructure and composition control.

[0042] 1-3, a variable bias cathodic arc device 10 (FIG. 1) and method 200 (FIG. 2) result in a cathodic arc TiSiVN or TiSiVCrN coated layered substrate structure 100 (FIG. 3), as described below.

[0043] FIG. 1 illustrates a variable bias cathodic arc device 10 embodied by the present disclosure. In FIG. 1, chamber 1 is defined by double walls 2 and 3 forming a double-walled chamber 1 to which a reactive gas can be supplied. In certain embodiments of the present disclosure, the reactive gas is nitrogen (N2). Double walls 2 and 3 of chamber 1 form electrodes that are connected to an electrical circuit 7 and thus function as anodes.

[0044] 1 and 2, in step 205, a consumable cathode 4 is placed in chamber 1. According to certain aspects of the present disclosure, consumable cathode 4 is composed of titanium, silicon, vanadium, and sometimes chromium. Consumable cathode 4 extends into double-walled chamber 1 and into a reactive gas, e.g., N2, in chamber portion 1a. In step 210, substrate 6 is placed in conjunction with a variable bias, thereby positioning substrate 6 to be coated by variable bias cathodic arc device 10, as described below. As embodied by the present disclosure, steps 205 and 210 can be reversed, with the reactive gas being placed in the chamber and then the cathode and substrate being placed in the vacuum chamber.

[0045] In step 215, a reactive gas is supplied to the variable bias cathodic arc device 10 in the chamber 1. According to certain aspects of embodiments of the present disclosure, the reactive gas includes at least one of nitrogen (N2) and oxygen (O2).

[0046] The variable bias cathodic arc device 10 includes an electrical circuit 7. In step 220, the electrical circuit 7 can generate an arc or electrical pulse 5 (hereinafter "arc 5") between a cathode and an anode. The electrical circuit 7 also generates a negative charge on the substrate 6 being coated by the cathodic arc process 200 and the variable bias cathodic arc device 10.

[0047] As the arc 5 crosses the consumable cathode 4, the interaction creates energetic metal ions 8. In step 225, the energetic metal ions 8 are ejected from the consumable cathode 4 by the arc 5 passing through it.

[0048] In step 230, the energetic metal ions 8 are accelerated towards the article or substrate 6 to be coated. Because the energetic metal ions 8 have a positive charge, the positively charged energetic metal ions 8 can be accelerated towards the substrate 6 by placing a negative charge on the article or substrate 6 to be coated. That is, a negative voltage (bias) is applied to the substrate by the circuit 7.

[0049] As embodied by the present disclosure, the bias is varied at a sub-hertz frequency. Thus, the velocity of the energetic metal ions 8 through the reactive gas in the chamber portion 1a can be controlled. If the bias is increased to a sufficiently high, yet still sub-hertz, level, the energetic metal ions 8 travel fast enough through the reactive gas to allow non-reaction to occur and deposit metal as at least one erosion-resistant coating layer 120 (FIG. 3) on the article or substrate 6. Then, in step 235, if the sub-hertz bias is reduced (changed) to a lower level, the energetic metal ions 8 have sufficient time to react with the gas, e.g., N2, and deposit the erosion-resistant coating layer 120 on the article or substrate 6. Also, any consumable cathode constituent, e.g., Si and V; chromium (Cr) and V; or one of Si, V, and Cr, can be included in the energetic metal ions 8.

[0050] In step 240, the process continues by repeating acceleration and deceleration steps 230 and 235, respectively, until the desired thickness of the erosion resistant coating layer 120 (FIG. 3) is achieved. This constant cycling or bias variation occurs throughout the deposition process, resulting in a metallurgical structure that is microstructured in the erosion resistant coating layer 120. The microstructure of the erosion resistant coating layer 120 (FIGS. 3 and 4) can enhance the overall properties of the coating. The variable bias cycling action forms the erosion resistant coating layer 120, such as titanium nitride SiV(Cr), then TiV(Cr), then titanium nitride SiV(Cr), etc. (with any doping constituents) until the coating cycle is complete. This variation in the layers of the coated layered substrate structure 100 and erosion resistant coating layer 120 (see FIG. 4) can increase the hardness and resistance to erosion through the coating.

[0051] Cathodic arc coatings embodied by the present disclosure can be up to 400% more durable in post-steam erosion tests than known coatings applied by thermal spraying, 10-20 times thinner, and 75-95% lighter. They are applied using essentially the same hardware as conventional cathodic arc TiN, yet are approximately 24 times more erosion resistant as deposited and 14 times more erosion resistant after steaming than conventional cathodic arc TiN. Therefore, they have the potential to reduce erosion damage to steam turbine blades without introducing significant aerodynamic drawbacks.

[0052] As embodied by the present disclosure, the plasma in the arc 5 for the variable bias cathodic arc process 200 is approximately 10 -1 Hz to about 1 Hz. Furthermore, in certain aspects of the present disclosure, the plasma in the arc 5 from the variable bias cathodic arc process 200 can be generated with a sub-hertz variable bias. As embodied by the present disclosure, the variable bias can be varied over time and have an approximately sinusoidal waveform with a frequency in the range of 0.1 Hertz (Hz) to about 1 Hz.

[0053] The plasma lifetime in the arc 5 for each impulse of the variable bias cathode arc is 10 -4 During arc discharge, the individual plasmoids may 4 meters per second (ms -1 ) and directed toward the substrate 6. The substrate 6 is not heated by any external heat source before, during, or after the process 200. The nucleation of TiN occurs on the energetic metal ions 8, and the layer is composed of sub-nano or nanoparticles on the substrate 6.

[0054] As embodied by the present disclosure, process 200 applies a variable bias to the substrate 6 being coated. The sub-hertz variable bias allows for beneficial problem-solving effects. The sub-hertz variable bias cathodic arc process 200, as embodied by the present disclosure, is performed at a variable bias waveform frequency of less than about 1 Hz. A sub-hertz variable bias cathodic arc having a variable bias waveform frequency of less than about 1 Hz can result in nanoscale layers, with the layers alternating in composition via the variable bias.

[0055] According to one aspect of the present disclosure, the sub-hertz variable bias can be at one level for up to approximately 1.5 to 3.5 seconds and transition to another level for another approximately 1.5 to 3.5 seconds. Other time intervals are within the scope of embodiments.

[0056] The coated layered substrate structure 100 exhibits improved erosion resistance during deposition, retention of erosion resistance after steam exposure up to approximately 600°C, and reduced mass change upon steam oxidation. The sub-hertz variable bias cathodic arc process 200 may also enable the deposition of some coatings that may have spalled during deposition with constant bias processes.

[0057] The coated layered substrate structure 100 has a compositional chemistry as embodied by the present disclosure that includes titanium nitride (TiN). TiN is considered an erosion-resistant coating that is resistant to steam oxidation. The compositional chemistry includes vanadium (V), silicon (Si), and chromium (Cr), which may be added constituents to the TiN of the consumable cathode during variable bias cycling.

[0058] Evaporating a TiSiV cathode to form TiSiVN (or TiSiVCr cathode to form TiSiVCrN) results in improved performance. Si doping is known to increase the hardness and oxidation resistance of TiN under conditions relevant to steam turbine operation. V doping is known to reduce residual stress in TiN. Furthermore, V doping of TiSiN can promote the formation of thermodynamically stable rutile phase titanium dioxide during steam oxidation, rather than the metastable anatase phase titanium dioxide.

[0059] The chart below shows the constituents of the consumable cathode 4. The chart also provides the resulting constituent ranges for each erosion resistant coating layer 120. [Table 1]

[0060] Furthermore, as embodied by the present disclosure, Si and V co-doping of TiN under the influence of a sub-hertz variable bias cathodic arc process can result in improved post-steam erosion protection during and after service of a steam turbine.

[0061] The above figures illustrate some of the processes involved in some embodiments of the present disclosure. In this regard, each figure or block within the flow diagrams of the figures represents a process associated with the described method embodiment. It should also be noted that in some alternative implementations, the operations described in the figures or blocks may occur out of the order shown in the figures, or may actually be performed substantially simultaneously or in reverse order, depending on the operations involved, for example. Those skilled in the art will also recognize that additional blocks describing the processes may be added.

[0062] As used herein throughout this specification and claims, approximation language can be applied to modify any quantitative expression that can be varied to a reasonable extent without resulting in a change in the basic function involved. Thus, values ​​modified by terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some instances, approximation language can correspond to the precision of the instrument used to measure the value. Herein and throughout this specification and claims, range limitations are combinable and / or interchangeable, and unless the context or language dictates otherwise, such ranges are identified and include all subranges encompassed therein.

[0063] The corresponding structure, material, acts, and equivalents of all means-plus-function or step-plus-function elements in the following claims are intended to encompass any structure, material, or acts for performing that function in combination with other specifically claimed claim elements. The description of the present disclosure has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The present embodiments were chosen and described in order to best explain the principles and practical application of the disclosure and to enable others skilled in the art to understand the disclosure in various embodiments with various modifications as suited to the particular uses envisioned. [Explanation of symbols]

[0064] 1 chamber 1a Chamber part 2 double wall 3 double wall 4 Consumable cathode 5 Electric pulse, arc 6 PCB 7 Electrical Circuits 8. High-energy metal ions 10 Cathodic Arc TiSiVN Coating System, Variable Bias Cathodic Arc Device 100 Layered substrate structure coated with cathodic arc titanium silicon vanadium nitride (TiSiVN) or titanium silicon vanadium chromium nitride (TiSiVCrN), cathodic arc TiSiVN coating system 120 Erosion-resistant coating, erosion-resistant coating layer 200 Process, method, variable bias cathodic arc process

Claims

1. 1. A cathodic arc coating system comprising: Titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN) disposed on a substrate (6); Alternating layers of titanium vanadium chromium nitride (TiVCrN) and titanium silicon vanadium nitride (TiSiVCrN) disposed on a substrate (6). The cathodic arc coating system comprises alternating layers of at least one of:

2. The cathodic arc coating system of claim 1 , wherein the alternating layers have a thickness ranging from about 1 nanometer (nm) to about 100 nm.

3. The cathodic arc coating system of claim 1 , wherein the alternating layers have a thickness in the range of about 5 nanometers (nm) to about 100 nm.

4. The cathodic arc coating system of claim 1 , wherein the alternating layers have a thickness of about 10 nanometers (nm).

5. 10. The cathodic arc coating system of claim 1, wherein the alternating layers are deposited on the substrate (6) by a sub-hertz variable bias cathodic arc.

6. 2. The cathodic arc coating system of claim 1, wherein the alternating layers are deposited on the substrate (6) by a sub-hertz variable bias cathodic arc, the sub-hertz variable bias varying with time as a sine wave, the sine wave having a frequency in the range of about 0.1 hertz (Hz) to about 1 Hz.

7. 10. The cathodic arc coating system of claim 1, wherein the alternating layers are deposited on the substrate (6) by a sub-hertz variable bias cathodic arc, the sub-hertz variable bias being varied periodically with time, and wherein one or more periodic features are represented by a frequency within a range of 0.1 hertz (Hz) to about 1 Hz.

8. 2. The cathodic arc coating system of claim 1, wherein the alternating layers are disposed on the substrate (6) by a sub-hertz variable bias, the sub-hertz variable bias comprising a modified variable bias waveform having a modified bias for controlling incorporation of at least one of vanadium (V), silicon (Si), and Cr.

9. Further comprising a chamber and a consumable cathode (4), the substrate (6) being placed in the chamber and the consumable cathode (4), the chamber acting as an anode; 9. The cathodic arc coating system of claim 8, wherein the sub-hertz variable bias generates a potential that attracts metal ions from the consumable cathode (4), causing energetic metal ions (8) to be emitted from the consumable cathode (4), and the energetic ions (8) to be accelerated toward the substrate (6).

10. 10. A cathodic arc coating system according to claim 9, wherein the substrate (6) is provided with a periodically varying negative charge.

11. 10. The cathodic arc coating system of claim 9, wherein the chamber contains nitrogen (N) gas therein.

12. 10. The cathodic arc coating system of claim 9, wherein the consumable cathode (4) comprises titanium (Ti), vanadium (V), silicon (Si), and sometimes chromium (Cr).

13. 1. A sub-hertz variable bias cathodic arc process comprising: Depositing a coating on a substrate (6), the coating comprising: Titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN) on the substrate (6); and Titanium vanadium chromium nitride (TiVCrN) and titanium silicon vanadium chromium nitride (TiSiVCrN) on the substrate (6) The process having at least one alternating layer of

14. The sub-hertz variable-bias cathodic arc process of claim 13, wherein the alternating layers have a thickness in the range of about 1 nanometer (nm) to about 100 nm.

15. 14. The sub-hertz variable-bias cathodic arc process of claim 13, wherein the step of depositing the alternating layers comprises depositing by a sub-hertz variable-bias cathodic arc.

16. 16. The sub-hertz variable bias cathodic arc process of claim 15, wherein the sub-hertz variable bias varies with time as an approximately sinusoidal wave, the approximately sinusoidal wave having a frequency within a range of 0.1 hertz (Hz) to about 1 Hz.

17. The sub-hertz variable bias causes vanadium (V) and silicon (Si) to Titanium vanadium nitride (TiVN) and titanium silicon vanadium nitride (TiSiVN); or Alternating layers of titanium vanadium chromium nitride (TiVCrN) and titanium silicon vanadium nitride (TiSiVCrN) 14. The sub-hertz variable bias cathodic arc process of claim 13, including a modified variable bias waveform having a reduced maximum voltage bias to incorporate into said alternating layers of.

18. placing a consumable cathode (4) in the chamber; placing the substrate (6) in communication with the chamber, the chamber acting as an anode; disposing a reactive gas in the chamber; applying a sub-hertz variable bias to the substrate (6); generating an electric arc on the cathode, the arc crossing the face of the cathode; generating energetic metal ions (8) by said arc interacting with said consumable cathode (4); Emitting energetic metal ions (8) from the surface of the consumable cathode (4); accelerating the high energy ions (8) towards the substrate (6); 14. The sub-hertz variable bias cathodic arc process of claim 13, comprising:

19. applying the sub-hertz variable bias applying the sub-hertz variable bias at a first voltage, wherein the emitted energetic metal ions (8) from the consumable cathode (4) pass through a reactant gas at a first velocity and partially react with the reactant gas, the reactant gas being nitrogen (N ２ ) and oxygen (O ２ ), wherein the released energetic metal ions (8) are deposited on the substrate (6); applying the sub-hertz variable bias at a second voltage, causing the emitted energetic metal ions (8) to pass through the reactant gas at a second velocity within the chamber, and at the second velocity, allowing the emitted energetic metal ions (8) to chemically react with the at least one of nitrogen and oxygen to form a reaction product, and the reaction product is deposited; applying the sub-hertz variable bias in a manner to systematically control the deposition efficiency of individual constituent elements from the consumable cathode (4) onto the substrate (6), wherein the abundance of one or more elements in the resulting microstructure of the coated substrate varies periodically as a function of distance from the original substrate surface in accordance with the applied variable bias, whether the constituent elements are ultimately incorporated into the microstructure of the coated substrate as part of a reaction product as described above or as partially reacted metal ions as described above; 20. The sub-hertz variable bias cathodic arc process of claim 18, comprising:

20. The consumable cathode (4) Titanium (Ti), vanadium (V), silicon (Si); and Titanium (Ti), vanadium (V), silicon (Si), and chromium (Cr) 20. The sub-hertz variable bias cathodic arc process of claim 19, including at least one of:

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