Electrolytic polishing method for titanium or titanium alloys using ionic solutions

Abstract

To provide a simple method for electropolishing titanium or titanium alloys without using organic electrolytes containing perchlorates or alcohols. [Solution] A method for producing electropolished titanium or titanium alloy is provided, which includes a step of anodic polarization of titanium or titanium alloy using a dry ionic liquid containing halide ions.

Description

[Technical Field]

[0001] This invention relates to the field of techniques for electrolytic polishing methods of titanium or titanium alloys. [Background technology]

[0002] Titanium is widely used in the fields of biocompatible materials and aerospace materials. In these applications, electropolishing of the titanium surface is required. However, when titanium is electropolished in an aqueous solution, an oxide layer is formed. The presence of this oxide layer inactivates the surface of the titanium metal and hinders the anodic dissolution of titanium.

[0003] Furthermore, conventional electrolytic polishing processes for titanium are carried out in electrolytes containing perchlorates or alcohol solutions, which poses safety concerns. Perchlorates are explosive, and alcohol is flammable. In addition, the competition between oxygen evolution reactions results in low current efficiency, and there is the problem of repassivation due to water contained in the electrolyte.

[0004] Non-patent document 1 reports on the electropolishing of titanium in an ionic liquid. Ionic liquids are liquids composed solely of ions and possess properties such as low volatility, flame retardancy, and ionic conductivity. The ionic liquid described in this document does not contain halide ions. Furthermore, electropolishing is not possible unless the titanium surface is mechanically polished beforehand to remove the oxide film.

[0005] Non-patent document 2 reports on the electrolytic polishing of titanium in a mixed electrolyte of choline chloride and ethylene glycol (deep eutectic solvent).

[0006] Non-patent document 3 reports on the electrolytic polishing of titanium in a mixed electrolyte of choline chloride and alcohol (deep eutectic solvent).

[0007] Patent Document 1 describes an ionic liquid composed of an aliphatic quaternary ammonium cation. Although there is a general description of electropolishing, in the examples, electropolishing of metals is not carried out, and halide ions are not added.

[0008] Non-Patent Document 4 reports the electropolishing of titanium in an ionic liquid containing an imidazolium cation. When the anion is (bis(trifluoromethylsulfonyl)amide), a smooth surface is obtained when anodic dissolution is carried out at a constant current. On the other hand, when the anion is chloride ion, smoothing is not achieved.

[0009] Non-Patent Document 5 reports the anodic dissolution of titanium in an amide-type ionic liquid containing chloride ions and trichloride ions. This document describes that the titanium electrode is activated by trichloride ions (Cl3 - ). Also, this document reports that anodic dissolution of titanium was possible in an ionic liquid containing both chloride ions and trichloride ions, and that trichloride ions (Cl3 - ) play an important role in the dissolution of titanium. Further, in the photograph of Fig. 3(b), the surface of titanium anodically dissolved at a potential of 1 V with reference to the potential of the Ag electrode (Ag|Ag(I)) immersed in an ionic liquid containing 0.1 mol L -1 of Ag salt is not smoothed and does not have a gloss.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

[0012] The present invention aims to provide a method for electropolishing titanium or titanium alloys that at least partially solves the problems of the conventional method, and a method for manufacturing electropolished titanium or titanium alloys. [Means for solving the problem]

[0013] In relation to the aforementioned problems, the present inventors have found that titanium can be electropolished by using an ionic liquid containing halide ions, as one example, and have completed the present invention which incorporates this as one embodiment.

[0014] In relation to the aforementioned problems, the inventors have also discovered, as an example, that the repassivation of the titanium surface during the electropolishing of titanium can be avoided by using an ionic liquid that does not contain trace amounts of water or is substantially free of water, and have completed the present invention which incorporates this as one embodiment.

[0015] In Non-Patent Document 5, it is reported that trichloride ions (Cl3 - ) contained in an ionic liquid are important for the anodic dissolution of titanium. Trichloride ions (Cl3 - ) are oxidizing agents, unlike chloride ions (Cl - ). Also, seawater contains chloride ions (Cl - ), and it has been known that this causes corrosion of metals such as pipes. However, titanium is known to exhibit corrosion resistance comparable to that of platinum against seawater due to passivation of its surface (Hidehito Oyama, "Titanium Materials", Surface Technology, Vo. 73, No. 1, 2022). Therefore, it was considered impossible to anodically dissolve titanium by adding only chloride ions (Cl - ) to an ionic liquid without adding trichloride ions (Cl3 - ). However, the inventors of the present invention repeated various studies and were able to electropolish titanium by using an ionic liquid containing halide ions. This was unexpected and a great surprise. Also, this corresponds to uniform corrosion rather than local corrosion.

[0016] The present invention includes the following embodiments. [1] A method for producing an electropolished titanium or titanium alloy, comprising a step of anodically polarizing titanium or a titanium alloy using a dried ionic liquid containing halide ions. [2] The production method according to Embodiment 1, wherein the halide ions are selected from the group consisting of chloride ions, bromide ions, and iodide ions. [3] The production method according to Embodiment 1, comprising a step of preparing a titanium or titanium alloy whose oxide film has not been removed by mechanical polishing in advance as the titanium or titanium alloy to be electropolished. [4] The production method according to Embodiment 1, wherein the ionic liquid is preferably a hydrophobic ionic liquid. [5] The hydrophobic ionic liquid contains an anion and a cation, The anion is a halide ion, tetrafluoroborate, hexafluorophosphate, bis(fluoroalkylsulfonyl)amide, bis(trifluoromethylsulfonyl)amide (TFSA - ), selected from the group consisting of bis(fluorosulfonyl)amide, dicyanoamide, etc. The manufacturing method according to Embodiment 4, wherein the cation is selected from the group consisting of dialkylimidazolium, dialkylpyrrolidinium, alkylpyridinium, dialkylpyridinium, dialkylpiperidinium, aliphatic quaternary ammonium, quaternary phosphonium, and those obtained by replacing at least one carbon atom of the alkyl chain with a hydrogen atom or an oxygen atom, or by replacing at least one hydrogen atom with a fluorine atom. [6] The manufacturing method according to Embodiment 1, wherein the ionic liquid is an ionic liquid that has been dried by vacuum drying, drying with a dehydrating agent or a water-absorbing substance, or drying with a drying gas. [7] The manufacturing method according to Embodiment 1, wherein electropolishing is performed until the surface of titanium or a titanium alloy is polished. [8] The manufacturing method according to Embodiment 1, wherein electropolishing is performed until the surface of the titanium or titanium alloy is smoothed. [Effects of the Invention]

[0017] One effect of the present invention is that titanium or titanium alloys can be electropolished. [Brief explanation of the drawing]

[0018] [Figure 1-1] This shows an example configuration for performing electrolytic polishing of titanium. [Figure 1-2] This shows an example configuration for performing electrolytic polishing of titanium. [Figure 2] The current behavior during constant potential electrolysis at 0 V is shown with and without chloride ions. The bottom row shows the case without Cl-, and the top row shows the case with Cl-. [Figure 3] This shows the current density of a titanium electrode subjected to anodic oxidation at a constant potential. [Figure 4]This image shows an optical microscope photograph of the titanium surface at an electrical charge of 50 C cm⁻². [Figure 5] This image shows a scanning electron microscope image of the titanium surface at an electrical charge of 50 C cm⁻². The titanium surface was polished using #800 waterproof abrasive paper before electrolysis. [Figure 6] The current behavior of titanium electrodes using methods A and B is shown. Method A is shown at the bottom, and method B is shown at the top. [Figure 7] These are optical microscope images obtained using methods A and B. [Modes for carrying out the invention]

[0019] In one embodiment, the present invention provides a method for electropolishing titanium or a titanium alloy using an ionic liquid. An ionic liquid is a liquid composed solely of ions and possesses properties such as low volatility, flame retardancy, and ionic conductivity.

[0020] In one embodiment, the ionic liquid comprises constituent cations and anions, and further includes halide ions. Examples of halide ions include fluoride ions, chloride ions, bromide ions, and iodide ions. In one embodiment, the halogen ions, fluoride ions, chloride ions, bromide ions, or iodide ions are, for example, 0.001 mM to 1 M, 0.0025 mM to 0.9 M, 0.005 mM to 0.8 M, 0.01 mM to 0.7 M, 0.02 mM to 0.6 M, 0.03 mM to 0.5 M, 0.04 mM to 0.4 M, 0.05 mM to 0.3 M, 0.06 mM to 0.25 M, 0.07 mM to 0.2 M, 0.08 mM to 0.15 M, 0.09 mM to 0.1 M, 0.1 mM to 0.1 M, 0.2 mM to 80 mM, 0.3 mM to 70 mM, 0.4 mM to 60 mM, 0.5 mM to 50 mM, 0.6 mM to 40 mM, 0.7 mM to 30 mM, 0.8 mM to 20 mM, 0.9 mM It can be contained in ionic liquids at concentrations of mM to 10 mM, for example, 0.1 mM to 5 mM. M is where M stands for moles (L). -1 It represents.

[0021] In one embodiment, the ionic liquid is a dry ionic liquid. In this specification, "dry" means that the ionic liquid does not contain or substantially contains no water. When titanium is electropolished using an ionic liquid, if water is present in the system, an oxide film may form on the surface of the titanium, which can hinder the anodic electrolysis of the titanium. An ionic liquid that is substantially water-free means that when titanium is electropolished using the ionic liquid, it contains only a trace amount of water such that no oxide film is formed on the surface of the titanium, or if it is formed, it is quickly removed, and the anodic electrolysis of the titanium proceeds without being hindered. In this specification, an ionic liquid that is substantially water-free may be referred to as a sufficiently dry ionic liquid.

[0022] Ionic liquids can be dried by conventional methods. In one embodiment, ionic liquids can be dried by vacuum drying. In another embodiment, ionic liquids can be dried with a dehydrating agent or water-absorbing substance such as molecular sieves or zeolites. In yet another embodiment, ionic liquids can be dried with a drying gas.

[0023] In some embodiments, the ionic liquid may be a hydrophobic ionic liquid. In some embodiments, the ionic liquid is liquid at room temperature (25°C). In some embodiments, the ionic liquid may have low volatility. In some embodiments, the ionic liquid may be flame retardant. Flame retardancy refers to the property of a material to resist combustion when directly exposed to a flame.

[0024] Examples of anions include halide ions, tetrafluoroborates, hexafluorophosphates, bis(fluoroalkylsulfonyl)amides, and bis(trifluoromethylsulfonyl)amides (TFSA). - Examples include, but are not limited to, bis(fluorosulfonyl)amides and dicyanoamides. TFSA -Many ionic liquids composed of these materials are preferable because they have a wide potential window, low volatility, are flame-retardant, and are hydrophobic.

[0025] Examples of cations include, but are not limited to, dialkylimidazolium, dialkylpyrrolidinium, dialkylpyridinium, dialkylpiperidinium, aliphatic quaternary ammonium, quaternary phosphonium, and those obtained by replacing at least one carbon atom in the alkyl chain with a hydrogen or oxygen atom, or by replacing at least one hydrogen atom with a fluorine atom.

[0026] Known titanium alloys may be used. Examples of titanium alloys include, but are not limited to, α-type alloys, near α-type alloys, β-type alloys, near β-type alloys, and α+β-type alloys. Examples of titanium alloys include, but are not limited to, alloys of titanium with one or more of the following: aluminum (Al), tin (Sn), molybdenum (Mo), zirconium (Zn), chromium (Cr), palladium (Pd), vanadium (V), niobium (Nb), iron (Fe), nickel (Ni), and hafnium (Hf). Titanium alloys include Ti-5Al-2.5Sn alloy, Ti-5Al-5Sn-2Zr-2Mo alloy, Ti-8Al-1Mo-1V alloy, Ti-3Al-2.5V alloy, T i-6Al-4V alloy, Ti-6Al-4V-2Sn alloy, Ti-6Al-6V-2Sn alloy, Ti-6Al-7Nb alloy, Ti-6Al-2Sn-4Zr-6Mo alloy, Ti-6Al-2Sn-4Zr-2Mo alloy, Ti-13V-11Cr-3Al alloy, Ti-3Al-8V-6Cr-4Mo-4Zr alloy, Ti-0.15Pd alloy, Ti -10V-2Fe-3Al alloy, Ti-29Nb-13Ta-4.6Zr alloy, Ti-13V-11Cr-3Al alloy, Ti-8Mo-8V-2Fe-3Al alloy, IMI Examples include, but are not limited to, 685 alloy, Ti1100 alloy, Ti62A alloy, Beta-C alloy, Ti-15-3 alloy, and Ti-6Al-4V-ELI alloy.

[0027] In one embodiment, the applied potential when electropolishing titanium or a titanium alloy may be -1.4~0 V, -1.2~0 V, -1.0~0 V, -0.9~0 V, -0.8~0 V, -0.7~0 V, -0.6~0 V, -0.5~0 V, -0.4~0 V, -0.3~0 V, -0.2~0 V, for example, -0.1~0 V (against Ag|Ag(I)). By applying a potential, the titanium at the anode is electrolyzed, i.e., the titanium dissolves. In this specification, this may be referred to as anodic dissolution or anodic polarization of titanium. In this specification, these terms are interchangeable.

[0028] In one embodiment, titanium or a titanium alloy can be electropolished with a specified current. The current density when electropolishing titanium or a titanium alloy is 0 μA cm². -2 ~10 mA cm -2 , 0.1 μA cm -2 ~5 mA cm -2 , 0.2 μA cm -2 ~2 mA cm -2 , 0.3 μA cm -2 ~1 mA cm -2 , 0.4 μA cm -2 ~0.5 mA cm -2 , 0.5 μA cm -2 ~0.4 mA cm -2 , 1 μA cm -2 ~0.3 mA cm -2 , 2 μA cm -2 ~0.2 mA cm -2 , 3 μA cm -2 ~0.1 mA cm -2 , 4 mA cm -2 ~50 mA cm -2 , 5 mA cm -2 ~40 mA cm -2 , 6 mA cm -2 ~30 mA cm -2 7 mA cm -2 ~20 mA cm -2 , 8 mA cm -2 ~15 mA cm -2, 9 mA cm -2 ~12 mA cm -2 For example, 10 mA cm -2 This is possible, but not limited to this. When electricity is applied, the titanium in the anode is electrolyzed, and the titanium dissolves.

[0029] In one embodiment, electropolishing of titanium or titanium alloys of a desired shape and size can be performed by applying a controlled potential. In one embodiment, the applied potential may be 0 V (vs. Ag|Ag(I)), but is not limited to this. While not wishing to be bound by any particular logic, the inventors believe that electropolishing of titanium or titanium alloys using an ionic liquid in the presence of halide ions can remove the oxide film on the surface of titanium or titanium alloys. Furthermore, while not wishing to be bound by any particular logic, the inventors believe that once the oxide film on the surface of titanium or titanium alloys is removed, electropolishing of titanium or titanium alloys can be performed without applying an excessive voltage.

[0030] In one embodiment, the temperature when electropolishing titanium or a titanium alloy may be, but is not limited to, 20-120°C, 25-100°C, 30-95°C, 37-90°C, 40-85°C, 50-80°C, 60-80°C, or, for example, 0-80°C.

[0031] In one embodiment, when electropolishing titanium or a titanium alloy, the amount of current applied (C cm) -2 ) is 1-200 C cm -2 , 2-150 cm -2 , 5~100 C cm -2 , 10-90 cm -2 , 20~80 C cm -2 , 30-70 cm -2 , 40-60 cm -2 For example, 50°C cm -2The potential can be applied up to the point where this occurs, but is not limited to this. In one embodiment, electropolishing of titanium or a titanium alloy may be carried out until the surface of the titanium is polished. Then, titanium of the same shape or dimensions is subjected to the current applied to the titanium surface until it is polished (C cm). -2 The potential can be applied until the desired result is reached. The glossiness of the titanium surface can be inspected by any inspection means, such as a laser microscope, gloss meter, optical microscope, or visual inspection, but the inspection method is not limited to these.

[0032] In one embodiment, electropolishing of titanium or a titanium alloy can be performed for 1 minute to 12 hours, 5 minutes to 10 hours, 10 minutes to 6 hours, 30 minutes to 5 hours, or 1 hour to 4 hours, but is not limited to these.

[0033] In one embodiment, the surface of titanium or a titanium alloy can be smoothed by electropolishing. In another embodiment, the surface of titanium or a titanium alloy can be polished by electropolishing. In another embodiment, the present invention provides a method for manufacturing titanium or a titanium alloy with a smoothed surface. In another embodiment, the present invention provides a method for manufacturing titanium or a titanium alloy with a polished surface. The smoothing can be evaluated by any inspection means, such as an electron microscope, laser microscope, or atomic force microscope.

[0034] In one embodiment, the presence of halide ions destroys or removes the oxide film on the titanium surface, enabling continuous anode dissolution of titanium without prior removal of the oxide film by mechanical polishing or other means. In another embodiment, the high viscosity of the ionic liquid limits the reaction rate by preventing the detachment of dissolved metal ions from the vicinity of the electrode, resulting in uniform dissolution in the in-plane direction and achieving smoothing and polishing of the metal surface. In yet another embodiment, using a sufficiently dried ionic liquid can suppress repassivation of the titanium surface. Furthermore, in yet another embodiment, when electropolishing titanium using this invention, high current efficiency can be expected without competition for oxygen generation.

[0035] While not wishing to be bound by any particular logic, the inventors believe that by using an ionic liquid as the electrolyte, metals can be electrochemically dissolved with high current efficiency without competition for oxygen generation. Furthermore, while not wishing to be bound by any particular logic, the inventors believe that because halide ions can act on oxide films, the addition of halide ions enables continuous dissolution of the titanium surface without the need for pretreatment such as mechanical polishing. Furthermore, while not wishing to be bound by any particular logic, the inventors believe that because ionic liquids are hydrophobic, it is relatively easy to reduce the amount of water in the electrolyte by drying, thereby suppressing the repassivation of the metal surface. In addition, while not wishing to be bound by any particular logic, the inventors believe that because the dissolved metal ions dissolve as halide complexes, the oxidation potential is lower than in conventional methods, enabling electropolishing at lower electrolytic voltages, and potentially increasing energy efficiency in addition to current efficiency.

[0036] Figures 1-1 and 1-2 show an example configuration for electrolytic polishing of titanium. 1 is the electrolytic cell, 2 is the ionic liquid, 3 is the titanium electrode, 4 is the counter electrode, 5 is the power supply or potentiostat, and (if present) 6 is the reference electrode. This configuration is merely an example, and the present invention is not limited thereto. The arrangement is also merely illustrative. [Examples]

[0037] The electropolishing method of the present invention is further illustrated by the following examples. However, these are for illustrative purposes only, and the disclosure is not limited thereto.

[0038] [Example 1] The electrochemical measurement is described below. The configuration shown in Figure 1 was prepared. A titanium plate with a 5 mm diameter exposed portion was used as the working electrode. As the electrolyte, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA, comparative example) or 0.5 mol L was used. -1BMPTFSA (Example), which is a solution of butylmethylpyrrolidinium chloride (BMPCl), was used. The following electrodes were used. Working electrode (WE): Ti Opposite (CE): Glassy Carbon Reference electrode (RE): 0.1 mol L -1 Ag thread (Ag|Ag(I)) immersed in AgCF3SO3 / BMPTFSA

[0039] The current behavior during constant potential electrolysis at 0 V is shown with and without chloride ions. The results are shown in Figure 2. According to Hidehito Oyama, "Titanium Materials," Surface Technology, Vol. 73, No. 1, 2022, page 3, paragraph "2.1 Pure Titanium and Corrosion-Resistant Titanium," titanium has corrosion resistance to seawater comparable to platinum. Therefore, the dissolution of titanium in the presence of chloride ions was surprising. Although the same document mentions that crevice corrosion (localized corrosion) may occur, in this example the entire titanium surface dissolved, which is not localized corrosion but general corrosion.

[0040] [Example 2] Next, titanium was anodic oxidized at a constant potential. 0.5 mol L of titanium was anodic oxidized at a constant potential of 0 V (against Ag|Ag(I) reference electrode). -1 Figure 3 shows the current density of the titanium electrode in BMPCl / BMPTFSA. The temperature was 80°C and the electrolyte was stirred. A scanning electron microscope (SEM) and an optical microscope were used to evaluate the surface of the titanium electrode. 50°C cm -2 Figure 4 shows an optical microscope image of the titanium surface at the point when the current flow reached the specified amount. It was confirmed that the titanium surface had become glossy. Figure 5 shows a SEM image of the same titanium. Before electrolysis, the surface was rough (Figure 5 left), whereas at 0 V, 80°C, and 50°C, the surface was glossy. -2 After electrolysis, the titanium surface was smoothed (Figure 5, right).

[0041] [Example 3] Next, the effect of water on the electropolishing of titanium was investigated. In Method A, BMPCl was added to pre-dried vacuum-cured BMPTFSA and dissolved at room temperature. Then, the resulting BMPTFSA+BMPCl mixture was used for electropolishing of titanium. In Method B, BMPCl was added to pre-dried vacuum-cured BMPTFSA, dissolved, and then dried under reduced pressure at 120°C. Then, the resulting BMPTFSA+BMPCl mixture was used for electropolishing of titanium. The results are shown in Figure 6. In Method A, where water was not removed, no oxidation current of titanium was observed, and the titanium was not electropolished. In Method B, where water was removed by vacuum drying, the titanium was electropolished. Furthermore, photographs taken with an optical microscope are shown in Figure 7. In Method A, where water was not removed, the titanium did not dissolve (Figure 7 left). In Method B, where water was removed, the titanium dissolved and the surface became glossy (Figure 7 right). These results indicate that the presence of water in the electrolyte hinders the electropolishing of titanium.

[0042] As shown in Figure 2, an oxidation current was observed in titanium in the presence of chloride ions, and the titanium surface could be electropolished. This is due to the halide ions attacking the titanium. Furthermore, as shown in Figure 7, titanium could not be electropolished in the presence of water, but when an ionic liquid from which water had been removed, i.e., a dry ionic liquid, was used, the titanium surface could be electropolished. Therefore, from these results, a person skilled in the art would reasonably understand that titanium can be similarly electropolished with other ionic liquids as long as water is substantially absent and halide ions are present. [Industrial applicability]

[0043] The method disclosed herein may be used for the electropolishing of titanium or titanium alloys.

[0044] References 1. Hideto Oyama, "Titanium Materials," Surface Technology, Vol. 73, No. 1, 2022)

[0045] This specification references numerous documents, including patent applications and manufacturers' manuals. While the disclosures of these documents are not considered relevant to the patentability of the present invention, their entirety is incorporated herein by reference. More specifically, all referenced documents are incorporated herein by reference in the same manner as each individual document is specifically and individually indicated as being incorporated by reference. [Explanation of Symbols]

[0046] 1 electrolytic cell 2 Ionic liquids 3 Titanium electrodes 4. Opposite 5. Power supply or potentiostat 6 Reference electrode

Claims

1. A method for producing electropolished titanium or a titanium alloy, comprising the step of anodic polarization of titanium or a titanium alloy using a dry ionic liquid containing halide ions.

2. The manufacturing method according to claim 1, wherein the halide ion is selected from the group consisting of chloride ions, bromide ions, and iodide ions.

3. The manufacturing method according to claim 1, comprising the step of preparing titanium or a titanium alloy that has not had its oxide film removed by mechanical polishing in advance, as the titanium or titanium alloy to be electropolished.

4. The manufacturing method according to claim 1, wherein the ionic liquid is a hydrophobic ionic liquid.

5. The hydrophobic ionic liquid comprises anions and cations, The anion is a halide ion, tetrafluoroborate, hexafluorophosphate, bis(fluoroalkylsulfonyl)amide, bis(trifluoromethylsulfonyl)amide (TFSA - Selected from the group consisting of ), bis(fluorosulfonyl)amide, dicyanoamide, etc. The manufacturing method according to claim 4, wherein the cation is selected from the group consisting of dialkylimidazolium, dialkylpyrrolidinium, alkylpyridinium, dialkylpiperidinium, aliphatic quaternary ammonium, quaternary phosphonium, and those obtained by replacing at least one carbon atom of the alkyl chain with a hydrogen atom or an oxygen atom, or by replacing at least one hydrogen atom with a fluorine atom.

6. The manufacturing method according to claim 1, wherein the ionic liquid is an ionic liquid that has been dried by vacuum drying, drying with a dehydrating agent or a water-absorbing substance, or drying with a drying gas.

7. The manufacturing method according to claim 1, wherein electropolishing is performed until the surface of titanium or a titanium alloy is polished.

8. The manufacturing method according to claim 1, wherein electropolishing is performed until the surface of titanium or a titanium alloy is smoothed.

Images