Surface hardening of Group IV metals

Abstract

A method for case-hardening a group IV metal or a group IV metal alloy, and a component hardened by this method are provided. [Solution] The method comprises the steps of: preparing a workpiece of a group IV metal or a group IV metal alloy, wherein the workpiece is in its final shape; nitriding the workpiece in a nitriding atmosphere containing NH as the nitride species at a first temperature of 450°C to 750°C for a nitriding time of at least 16 hours to form a hydrogen-containing diffusion zone; and a second temperature up to 750°C and up to 10 -4 The method includes removing hydrogen from a hydrogen-containing diffusion zone over a hydrogen removal time of at least 4 hours at a partial pressure of H2 in mbar to form a hydrogen-deficient diffusion zone. This method and its components are useful for implants, particularly dental implants.

Description

[Technical Field]

[0001] This invention relates to the hardening of Group IV metals or alloys. Specifically, a method for hardening Group IV metals or Group IV metal alloys by heat curing, and hardened Group IV metal or Group IV metal alloy components are provided. This method and components are useful for implants, particularly dental implants. [Background technology]

[0002] Titanium is a light metal with tensile strength comparable to stainless steel, forming a titanium oxide layer on its surface that naturally reacts with oxygen to provide corrosion resistance. These characteristics make titanium highly attractive for many fields, including aerospace and military applications, as well as for industrial use. Furthermore, its biocompatibility makes it suitable for medical applications, such as implants. While the naturally formed titanium oxide layer is thin, for example, on a nanometer scale, in certain applications, it may be desirable to modify the surface-adjacent regions of titanium and its alloys. It is well known that titanium and other Group IV metals can be hardened by interstitial oxygen and other elements, and that the hardening of titanium must be carried out at the lowest possible temperature to avoid grain growth and overall material distortion associated with phase transformation or creep.

[0003] Prior art for hardening titanium is known. For example, European Patent Application Publication No. 885980 discloses a method for forming a surface layer having high hardness and tribological properties on a titanium or zirconium component. This method may include raising the temperature of the component above 500°C to obtain a homogeneous temperature; injecting a treatment gas containing ammonia, hydrocarbons and / or oxidizing gases onto the component to be treated, which has been raised to a temperature above 500°C; and maintaining the pressure in the furnace at at least 100 mbar for at least several minutes, depending on the desired treatment depth. When ammonia is used to treat titanium, Ti x N y A yellow surface layer is obtained.

[0004] Preisser et al., 1991 (HTM Harterei - Technische Mitteilungen 46 (1991) Nov. / Dez., No.6, Munich, DE) disclose high-pressure nitriding of titanium workpieces, in which the workpiece is treated with ammonia at a nitriding temperature of 700°C or 900°C and a pressure of 12 bar. The treated workpiece has an outer layer of TiN, and a layer of Ti2N is formed beneath the outer layer of TiN.

[0005] Japanese Patent Publication No. 2-25559 discloses nitriding a titanium workpiece using ammonia at 400°C to 850°C for at least 1 hour, and then treating it in an inert gas at at least 400°C for at least 1 hour to remove hydrogen from the workpiece. The treatment provides a layer of TiN on the workpiece.

[0006] Japanese Patent Publication No. 54-93700 discloses a method in which titanium undergoing a nitriding reaction is treated in an atmosphere of NH3 gas or an N2-H2 mixed gas, and then the titanium is heated to over 600°C in an inert atmosphere or vacuum to thermally decompose the hydride formed by the reaction.

[0007] In light of the prior art, there remains a need for an improved method for hardening titanium or other Group IV metals and their alloys, and the object of the present invention is to provide an improved surface hardening method for Group IV metals and their alloys. [Overview of the project]

[0008] The present invention relates to a method for case hardening a group IV metal or group IV metal alloy, comprising the steps of: preparing a workpiece of a group IV metal or group IV metal alloy, wherein the workpiece is in its final shape; nitriding the workpiece in a nitriding atmosphere containing NH3 as the nitride species at a first temperature of 450°C to 750°C and a partial pressure of NH3 of 0.5 bar to 2 bar for a nitriding time of at least 12 hours to form a hydrogen-containing diffusion zone; and a second temperature of 600°C to 750°C and a maximum of 10 -4The present invention relates to a method comprising the step of removing hydrogen from a hydrogen-containing diffusion zone at a partial pressure of H2 of mbar (pH2) over a hydrogen removal time of at least 4 hours to form a hydrogen-deficient diffusion zone.

[0009] This method includes a step of nitriding the workpiece. In this specification, this step may be referred to as the “nitriding step.”

[0010] This method includes a step of removing hydrogen from a hydrogen-containing diffusion zone. It should be understood that by exposing a workpiece treated with NH3 to low pressure, particularly a low partial pressure of H2, at high temperatures, hydrogen diffuses from the workpiece into the surrounding atmosphere and is thus removed from the workpiece. The hydrogen removal step may also be referred to as "diffusing hydrogen" or "diffusion step" from the hydrogen-containing diffusion zone, and these terms are interchangeable herein. Similarly, the hydrogen removal time may also be referred to as diffusion time, and these two terms are interchangeable herein.

[0011] The workpiece is prepared in its final shape. Dissolving nitrogen and hydrogen into the workpiece generally increases its volume, but the workpiece returns to its pre-treatment shape, i.e., its final shape. However, even if the workpiece is in its final shape after treatment, it is possible to further process it in ways that do not substantially affect the final shape, such as polishing.

[0012] Treatment with NH3, i.e., treatment at a first temperature of 450°C to 750°C, forms a diffusion zone in the group IV metal. This diffusion zone is thought to contain nitrogen and hydrogen in the solid solution, and usually the hydride of the group IV metal. Subsequent diffusion treatment, i.e., diffusion treatment at a second temperature of up to 750°C, forms another diffusion zone in the group IV metal. This diffusion zone contains nitrogen in the solid solution, but is hydrogen-deficient. Therefore, in this specification, the term "diffusion zone" may refer to either the diffusion zone after nitriding or the diffusion zone after diffusion treatment. The diffusion zone after nitriding but before diffusion treatment is generally called the "hydrogen-containing diffusion zone," and the diffusion zone after diffusion treatment is generally called the "hydrogen-deficient diffusion zone." However, the diffusion zone after hydrogen removal may also be called the "nitrogen diffusion zone."

[0013] The diffusion zone extends from the surface of the Group IV metal or Group IV metal alloy. In this specification, the diffusion zone is defined as having a microhardness from the surface of the Group IV metal to a core hardness of 50 HV. 0.005 It is thought to extend to a depth equal to the sum of the two. The diffusion zone may also be defined by thickness, in which case the thickness is such that the microhardness is 50 HV greater than the core hardness. 0.005The depth from the surface to the surface of the group IV metal is calculated from the depth equal to the sum of the two factors. Furthermore, treatment with NH3, i.e., treatment at a first temperature of 450°C to 750°C, forms a nitride layer on the surface of the group IV metal or group IV metal alloy. The group IV metal may be titanium, zirconium, or an alloy containing both titanium and zirconium. In this specification, the nitride layer of the group IV metal or group IV metal alloy may be collectively referred to as (Ti,Zr)N in the case of an alloy containing both titanium and zirconium. Regardless of the presence of the nitride layer, the diffusion zone is considered to extend from the surface of the group IV metal or group IV metal alloy, and the diffusion zone extends deeper than the nitride layer. Therefore, the diffusion zone can be considered to be below the nitride layer, or it can be considered to be between the nitride layer and the core of the group IV metal or group IV metal alloy. The nitriding process can also be considered to form a nitride layer of the group IV metal or group IV metal alloy on the surface of the workpiece, and to form a hydrogen-containing diffusion zone between the nitride layer and the core of the group IV metal or group IV metal alloy.

[0014] In the method of the present invention, ammonia (NH3) is used in the method of the present invention. When exposed to temperatures above 800°C, especially even higher temperatures, for example above 1000°C, NH3 dissociates into N2 and H2, and generally, N2 can also be used for metal nitriding. However, when NH3 is used as a nitriding species at up to 800°C, both nitrogen and hydrogen dissolve simultaneously in the metal. Specifically, the inventors believe that NH3 molecules on the metal surface split into N and H atoms at high temperatures, and both N and H atoms diffuse into the metal. NH3 is thought to provide a much higher "virtual partial pressure" of nitrogen than N2 alone, and a much higher virtual partial pressure of hydrogen than H2 alone; therefore, NH3 is a much stronger nitriding species than N2, and at the same time, a much stronger hydrogenation species than H2. The virtual partial pressure of H2 is shown in Figure 1 as pH2 as a function of different total pressures and the NH3:N2 ratio at 690°C. However, since interstitial hydrogen in group IV metals is thought to embrittle them, hydrogen is generally undesirable in the hardening of group IV metals. Furthermore, when group IV metals are treated with NH3, more hydrogen dissolves into the group IV metal compared to when they are treated with H2. Therefore, it can be expected that the adverse effects of interstitial hydrogen will be more pronounced when group IV metals are treated with NH3 compared to when they are treated with N2 and H2. However, the inventors have surprisingly found that by introducing hydrogen atoms from NH3, i.e., at 450°C to 750°C, the hydrogen atoms then diffuse from the group IV metal at a maximum of 750°C, for example, 400°C to 700°C, and especially at 600°C to 700°C, thereby preventing the embrittlement problem despite the increased amount of hydrogen in the group IV metal obtained by the nitriding process with NH3. Furthermore, the dissolution of hydrogen in Group IV metals also leads to the formation of hydrides, and it is known that removing hydrogen from Group IV metals containing Group IV metal hydrides by treatment at high temperatures exceeding 700°C, for example, results in grain refinement within the Group IV metal. The inventors believe that treating Group IV metals with NH3 results in a higher hydrogen concentration within the Group IV metal than treating them with H2, and therefore, more efficient grain refinement of Group IV metals can be achieved in this way compared to grain refinement obtained using H2.Therefore, when a group IV metal is treated with NH3 at 450°C to 750°C, and then hydrogen is removed from the group IV metal by diffusion at a maximum temperature of 750°C, for example, 400°C to 700°C, a hardened group IV metal with refined grain is obtained. Specifically, the hardened group IV metal has a refined core zone defined by the core hardness of the group IV metal, and a hydrogen-deficient diffusion zone due to nitrogen in the solid solution between the refined core zone and the surface of the group IV metal.

[0015] In nitriding, a nitriding atmosphere containing NH3 as the nitriding species is used. The partial pressure of NH3 can be freely selected, but it must be sufficient to dissolve the desired amounts of nitrogen and hydrogen in the group IV metal. If the partial pressure of NH3 is low, sufficient nitrogen will not dissolve in the group IV metal or group IV metal alloy, so the partial pressure of NH3 should generally be at least 1 mbar, preferably 0.5 bar to 2 bar at ambient pressure. If the partial pressure of NH3 is lower than the ambient pressure, the pressure may be reduced by any means as desired. For example, the partial pressure may be equal to the total pressure, i.e., the nitriding atmosphere may be pure NH3 containing unavoidable impurities, or the partial pressure may be reduced by adding further gas species to the nitriding atmosphere. The further gas species may be an inert gas or a gas species that provides a specific function. Since nitriding is carried out at a first temperature of 450°C to 750°C, nitrogen gas, i.e., N2, is considered an inert gas that does not cause nitrogen dissolution. Further inert gases are noble gases, such as argon and helium. The nitriding atmosphere is particularly preferably free of oxidizing species, such as CO2, O2, and N2O. It is even more preferably free of oxygen-containing species. By avoiding oxidizing and oxygen-containing species, it is ensured that the diffusion zone obtained by this method is free of interstitial oxygen or oxygen in the solid solution. However, since nanometer-scale oxide layers naturally form on the surface of Group IV metals in contact with air, components manufactured by this method may still have an unavoidable oxide layer on their surface. In this specification, nanometer-scale oxide layers are considered to have no adverse effect, and components having naturally formed nanometer-scale oxide layers are considered to be substantially free of oxide layers. Similarly, Group IV metals can contain an unavoidable amount of oxygen dissolved in them, and if a Group IV metal contains an unavoidable amount of oxygen dissolved in it, then the Group IV metal is substantially free of interstitial oxygen.

[0016] The nitriding atmosphere may further contain gas species that provide specific functions. For example, the nitriding atmosphere may contain carbon-containing gas species. Generally, carbon may dissolve in the group IV metal, but the concentration of the carbon-containing gas species must be low enough to form carbides or carbonitrides in the group IV metal. Generally, if the first temperature does not exceed 700°C, carbide formation is avoided. Typical carbon-containing gas species are alkanes (e.g., methane), alkenes (e.g., ethylene), and alkynes (e.g., acetylene). In addition, the carbon-containing gas species may contain nitrogen, but must not contain oxygen.

[0017] The nitriding atmosphere is preferably free of oxygen-containing species. However, in certain oxygen-containing species, the oxygen cannot be used to dissolve a very large amount of oxygen into the group IV metal. For example, CO can be included to obtain high carbon activity but without dissolving oxygen into the group IV metal. Furthermore, urea (H2NCONH2) may be used as a nitriding species or to produce NH3. For example, urea may be heated to produce a mixture of NH3, CO, and other species, and this mixture may be used as the nitriding atmosphere.

[0018] The hydrogen-containing diffusion zone is formed during the nitriding process at a first temperature of 450°C to 750°C. The nitriding time generally depends on the first temperature; at a first temperature of 450°C to 580°C, the nitriding process is generally undesirably slow, but if the first temperature is at least 580°C, for example, at least 581°C or at least 585°C, the nitriding rate of the workpiece is acceptable. When the first temperature is 700°C to 750°C, undesirable grain growth may be observed for group IV metals. Therefore, if grain growth is unacceptable, the first temperature must be at most 700°C, for example, 450°C to 700°C or 580°C to 700°C, for example, 582°C to 700°C. However, the increased amount of hydrogen in the hydrogen-containing diffusion zone allows for grain refinement brought about by the diffusion treatment that is sufficient to avoid the adverse effects of grain growth above 700°C. Thus, the present invention provides a method for enabling hardening of group IV metals at temperatures above 700°C while reducing the risk of undesirable grain growth. Table 1 shows preferred combinations of the first temperature and nitriding time.

[0019] [Table 1]

[0020] Particularly preferred combinations of first temperature and nitriding time are 450°C to 580°C and at least 24 hours (e.g., up to 200 hours); 580°C to 700°C and at least 12 hours (e.g., at least 16 hours or at least 20 hours) and up to 100 hours; and 700°C to 750°C and at least 1 hour and up to 50 hours. The most preferred combination of first temperature and nitriding time is 600°C to 700°C and at least 12 hours (e.g., at least 16 hours).

[0021] The nitriding atmosphere is preferably free of oxidizing species. However, in one example, the workpiece is treated to dissolve oxygen in the Group IV metal before the nitriding process or after the diffusion process. For example, a workpiece of Group IV, such as the final form of a Group IV metal or a Group IV metal alloy, or a workpiece of a Group IV metal or a Group IV metal alloy after the nitriding and diffusion processes, may be treated to have an oxygen diffusion zone containing interstitial oxygen, with the thickness of the oxygen diffusion zone being 10 μm to 100 μm from the surface. The oxygen diffusion zone has a microhardness from the surface of the Group IV metal that is 50 HV greater than the core hardness of the Group IV metal. 0.005 It may extend to a depth equal to the sum of the two. Near the surface, for example at a depth of 5 μm, the microhardness of the oxygen diffusion zone is 600 HV. 0.005 ~800HV 0.005 It is also possible that the oxygen diffusion zone is formed by first oxidizing a group IV metal to form an oxide layer on the group IV metal, and then treating the group IV metal having the oxide layer under vacuum to dissolve oxygen from the oxide layer in the group IV metal. Alternatively, the workpiece of the group IV metal or group IV metal alloy treated in the nitriding and diffusion steps may be treated in an oxidizing atmosphere to dissolve oxygen in the group IV metal or group IV metal alloy, or an oxide layer may be formed on the surface of the group IV metal or group IV metal alloy, and then treated in an oxidizing atmosphere, for example under vacuum, at a low partial pressure of the oxidizing species. The conditions for the oxidation and dissolution steps, such as temperature, time, and the partial pressure of the oxidizing species, may be the same as those for the nitriding and diffusion steps of the present invention with respect to the oxidizing species. When an oxygen diffusion zone is formed in a group IV metal, the diffusion step follows the nitriding step, and the hydrogen-deficient diffusion zone contains both oxygen and nitrogen.

[0022] Group IV metals and their alloys may be described from the perspective of their hardness. Group IV metals can be hardened by the dissolution of nitrogen, oxygen, and other elements in the metal. Regardless of any case-hardening, Group IV metals have a core hardness. Therefore, the core hardness generally corresponds to the hardness of the Group IV metal before case-hardening, such as the surface hardness. Hardness is generally measured in accordance with the DIN EN ISO6507 standard. The core hardness generally depends on a specific Group IV metal. When a Group IV metal is treated by the method of the present invention, the surface hardness is at least 200 HV 0.025 higher than the core hardness. The surface hardness is preferably analyzed using a load up to 50 g, that is, HV 0.05 However, unless otherwise specified, the value of the surface hardness is HV 0.025 The maximum load of 50 g, for example, HV 0.01 , HV 0.025 or HV 0.005 The surface hardness values are considered to be representative of the value of HV 0.025 The core hardness of grade 2 titanium is usually about 200 HV 0.025 and the core hardness of grade 5 titanium is usually about 300 HV 0.025 In the nitriding process, a diffusion zone extending to a depth where the microhardness from the surface of the Group IV metal becomes equal to the core hardness plus 50 HV 0.005 is obtained. Therefore, the thickness of the diffusion zone is calculated from the depth where the microhardness becomes equal to the core hardness plus 50 HV 0.005 to the surface of the Group IV metal.

[0023] Generally, the depth depends not only on the first temperature and nitriding time but also on the partial pressure of NH3. The higher the first temperature and the longer the nitriding time, the greater this depth. Generally, case-hardening is already obtained when this depth is about 1 μm, but this depth is preferably at most about 50 μm. The depth is usually 10 μm to 30 μm. Therefore, in the case-hardened Group IV metal or Group IV metal alloy, the depth of the diffusion zone containing nitrogen in the solid solution is at most 50 μm, for example, 10 μm to 30 μm. The microhardness of the diffusion zone is 50 HV higher than the core hardness 0.005From a hardness equal to the sum of the above to the hardness observed on the surface, for example, about 300 HV 0.005 From up to 1000HV 0.005 The hardness increases to the above value. In particular, when the surface has a (Ti,Zr)N layer, the hardness is 1000 HV at a depth of 2.5 μm from the surface. 0.005 ~1500HV 0.005 Generally, workpieces processed by the method of the present invention, such as components of the present invention, have very high surface hardness. However, the depth from the surface required to obtain very high hardness does not need to be particularly deep. Therefore, the component has a microhardness of HV, which is obtained at a depth of 2.5 μm from the surface. 0.005 This is explained.

[0024] In the diffusion step, hydrogen diffuses out of the hydrogen-containing diffusion zone, i.e., is removed from the hydrogen-containing diffusion zone. Hydrogen generally diffuses out of the hydrogen-containing diffusion zone when the partial pressure of the hydrogen-containing species is low, and in the method of the present invention, the diffusion step is specified in particular in terms of the partial pressure of H2 (pH2). The diffusion step may be carried out at a second temperature up to 750°C, but for practical reasons, the second temperature is usually at least 200°C. For example, the second temperature may be 300°C to 750°C, and especially 600°C to 700°C. A hydrogen-containing gas species, such as NH3, can dissociate into other gases in relation to H2 and other elements of the gas species, thereby allowing pH2 to be specified even if H2 is not included in the diffusion step, so pH2 is suitable for specifying the diffusion step. For example, Figure 1 shows pH2 as a function of the NH3:N2 ratio at different total pressures. In particular, pH2 should be as low as possible, for example, pH2 is up to 10 -5 It may be mbar, or pH2 may be up to 10 -6 The pressure may be mbar, and the diffusion process may be carried out in a vacuum. In this specification, "vacuum" means a total pressure of up to 10 mbar. -4 This means it is mbar, and pH2 is up to 10 -4 The composition is not limited to mbar. The conditions for the nitriding and diffusion steps can be selected independently. The partial pressure of H2 can be controlled as desired. For example, pH2 can be controlled when the total pressure is up to 10 -4The pH2 may be equal to the total pressure so that it is mbar, or the pH2 may be reduced by supplementing the nitride atmosphere with an inert gas and optionally reducing the total pressure.

[0025] The nitriding and diffusion processes may be carried out in the same furnace. For example, by directly exhausting the nitriding atmosphere, up to 10 -4 A pH of mbar or argon may be obtained, or the nitriding atmosphere may be replaced with an inert atmosphere, such as N2 or argon, before evacuating the furnace. Replacing the nitriding atmosphere with an inert atmosphere makes it easier to ensure that a sufficiently low pH of 2 is obtained because NH3 is removed from the furnace. Further steps may be included between the nitriding and diffusion steps. For example, the workpiece may be removed from the furnace in which the nitriding step is performed, cooled to ambient temperature, and then the diffusion step may be performed in the same or a different furnace. In addition to ensuring the removal of hydrogen from the hydrogen-containing diffusion zone, the diffusion step also redistributes interstitial nitrogen and nitrogen in the nitride layer. In particular, nitrogen moves deeper, and as a result, pushes deeper into the interface between the core and the diffusion zone. For example, when a Ti15Zr alloy is treated in the nitriding step, the hardness of the Ti15Zr alloy is 400 HV at a depth of 30 μm. 0.005 Although it was less than [a certain value], when a diffusion process was performed on the Ti15Zr alloy, the hardness was 400 HV at a depth of 50 μm. 0.005 It was less than (Figures 2 and 3).

[0026] In the diffusion process, even small amounts of contaminants can cause undesirable discoloration and other unwanted effects on the surface of the workpiece. For example, contaminants can prevent Group IV metals from retaining their metallic luster. Therefore, the partial pressures of NH3 and other undesirable species, such as CO2, O2, and N2O, can increase the total pressure in the diffusion process by up to 10 -4 To reduce the pressure to mbar, and / or to reduce the partial pressure of each species, especially the partial pressure of pH2, to a maximum of 10 -4 It is preferable to control this by including only inert gas species with a partial pressure of mbar, such as NH3 and any oxidizing species, e.g., CO2, O2, and N2O, with lower partial pressures, e.g., up to 10 mbar. -5 mbar or up to 10 -6It is particularly preferable that the concentration be mbar. Generally, inert gases, such as argon and N2, contain a sufficient amount of contaminants, especially O2. Therefore, when the goal is for a group IV metal to retain its metallic luster, it is preferable that only a very pure form of the inert gas be included in the diffusion process.

[0027] While metallic luster cannot be obtained when the surface layer is (Ti,Zr)N, the method of the present invention allows the treated workpiece to regain its metallic luster, making it impossible to distinguish the component of the present invention from the untreated workpiece by visual inspection. Therefore, if the workpiece has a mirror-polished appearance, that mirror-polished appearance is also found in the component after treatment by this method. In this specification, “mirror-polished appearance” is defined as a surface with an arithmetic mean deviation (Ra) roughness of less than 0.1 μm in accordance with the ISO 1302:2002 standard. For example, the Ra value can be measured using a Taylor-Hubson Surtronic S25 measuring over a length of 1.25 mm. A mirror-polished surface may also be called an N3 surface, and the two terms are interchangeable. In a preferred embodiment, a workpiece of a group IV metal is polished before nitriding the group IV metal to a surface roughness of less than 0.1 μm in accordance with the ISO 1302:2002 standard. A surface roughness of less than 0.1 μm is also observed in the workpiece after the diffusion process. Furthermore, if a mirror-polished appearance is important, the nitriding atmosphere must not contain carbon-containing molecules. If the nitriding atmosphere does not contain further carbon-containing molecules, commercially pure (CP) titanium, for example, grade 2 or grade 4, can be nitrided at at least 1100 HV while maintaining a mirror-polished appearance. 0.005 This can be obtained along with a surface hardness of at least 1100 HV. Therefore, the method of the present invention can obtain a surface hardness of at least 1100 HV. 0.005 This provides titanium components with a mirror-polished appearance.

[0028] Generally, the higher the temperature of the diffusion process, i.e., the higher the second temperature, the faster the diffusion. Therefore, it is preferable that the second temperature be as high as possible while preventing undesirable grain growth. A second temperature of up to 700°C is preferred, and for example, the second temperature may be 600°C to 700°C. Table 2 shows typical combinations of second temperature and hydrogen removal time that cover both the removal and retention of the nitride layer. Here, in order to ensure the removal of the nitride layer, the second temperature must be at least 600°C and the hydrogen removal time must be at least 4 hours.

[0029] [Table 2]

[0030] Generally, nitriding time and hydrogen removal time can be considered in combination, and the inventors have surprisingly found that when the nitriding time is at least 12 hours, for example at least 16 hours, particularly at a first temperature of 650°C to 700°C, a sufficient amount of nitrogen dissolves into the workpiece of a group IV metal or group IV metal alloy, and the nitride layer can be removed by applying a hydrogen removal time of at least 4 hours at a second temperature of at least 600°C, thereby obtaining a hardened component that does not have a nitride layer, particularly a visible nitride layer, on its surface while retaining a nitrogen diffusion zone. In particular, when the method of the present invention processes components of titanium-based alloys that do not contain titanium or zirconium, the surface hardness is 700 HV. 0.005 ~2000HV 0.005 This provides a component without a TiN layer. Similarly, when processing a component of zirconium or a group IV metal alloy containing at least 2 wt% zirconium, the hardness at a depth of 2.5 μm from the surface is 1000 HV. 0.005 ~1500HV 0.005 While it is possible to obtain the component, it lacks a nitride layer, and therefore its hardness requires a nitride layer.

[0031] To our surprise, the inventors have found that when processing components of titanium-based alloys that do not contain titanium or zirconium, the processed components retain a surface nitride layer of Ti2N but not TiN. Therefore, in this specification, the removal of nitrides from a component does not include the removal of Ti2N from components of titanium-based alloys that do not contain titanium or zirconium. Ti2N is visually indistinguishable from titanium or titanium alloys, whereas TiN is golden or yellow. Similarly, the nitrides of zirconium or zirconium alloys are also golden or yellow. By removing the golden or yellow nitride layer, the component regains its pre-treatment metallic luster and hardens by further possessing a nitrogen diffusion zone. Therefore, the present invention provides hardened components of Group IV metals having a metallic luster, such as titanium-based alloys that do not contain titanium or zirconium, zirconium, or zirconium alloys. Furthermore, these components do not exhibit the golden or yellow color due to nitrides of Group IV metals.

[0032] In one example, the nitriding and diffusion processes are repeated on the same workpiece. The nitriding and diffusion processes can be repeated any number of times as desired. Generally, the first repetition increases the surface hardness compared to a workpiece treated only once with the nitriding and diffusion processes.

[0033] Any group IV metal or group IV metal alloy is suitable for this method. In certain embodiments, the group IV metal is selected from titanium, titanium alloys, zirconium, and zirconium alloys. In this specification, the component may consist of a group IV metal or group IV metal alloy, for example, a titanium alloy or a titanium-zirconium alloy, or it may contain other materials. For example, the component may have a portion that is another material, polymer, glass, ceramic, or another metal, and an outer layer of titanium alloy or zirconium. Similarly, a workpiece processed by the method of the present invention may have a core made of another material. The outer layer does not need to completely cover the outer surface of the component. The component may be manufactured, for example, by additive manufacturing or 3D printing before being processed according to the method of the present invention.

[0034] The inventors have surprisingly discovered that when NH3 is used to harden Group IV metals or Group IV metal alloys, the presence of zirconium affects the available surface hardening. Regardless of whether the Group IV metal is titanium or zirconium, NH3 diffuses atoms N and H into the Group IV metal at low temperatures, forming hydrogen and nitrogen-containing diffusion zones. The inventors have found that, in particular, when zirconium is present in an amount of at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%), zirconium-containing Group IV metal alloys, especially zirconium-containing titanium-based alloys, allow for at least 5 times, for example about 10 times, greater nitrogen uptake than zirconium-free Group IV metal alloys, such as Grade 2, Grade 4, or Grade 5 titanium. The inventors have further observed that such high nitrogen uptake is not available when zirconium-containing titanium-based alloys are nitrided using N2 at, for example, at at least 800°C. Therefore, nitriding a titanium-based alloy containing zirconium or at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%) of zirconium at a first temperature of 450°C to 750°C using NH3 as the nitride species results in at least five times greater nitrogen uptake than when nitriding the alloy using N2 as the nitride species at at least 800°C. The present invention provides a solution to the problem of how to increase the nitrogen uptake of zirconium or a titanium-based alloy containing at least 2 wt% of zirconium. In addition to the increased nitrogen content dissolved in the hydrogen-containing diffusion zone, nitrides of the zirconium-containing titanium-based alloy are present on the surface of the titanium-based alloy after the nitriding process, and certain nitrides may be dissolved in the diffusion process or retained in a modified form.

[0035] In certain cases, a Group IV metal alloy is zirconium or a Group IV metal alloy containing at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%) of zirconium, for example, together with other metals, such as a titanium-based alloy containing 10 wt% to 20 wt% zirconium. For example, a Group IV metal may be a titanium-based alloy containing at least 5 wt% zirconium, or a zirconium-based alloy, such as pure zirconium. Typical zirconium-containing Group IV metals and Group IV metal alloys are Zr702 zirconium, titanium / niobium alloys, such as Ti13Nb13Zr and Ti15Zr (α alloy). When a group IV metal alloy, such as a titanium-based alloy, contains at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%) of zirconium, the nitriding process forms a much higher nitrogen content in the diffusion zone. Furthermore, when the alloy is a titanium-based alloy or contains titanium on the surface of a zirconium-containing group IV metal alloy, it forms a nitride layer of zirconium nitride (ZrN) and titanium nitride (TiN), e.g., (Ti,Zr)N. This nitride layer can be retained or removed in the diffusion process. In particular, when the zirconium content is 10 wt% to 20 wt%, at least 1000 HV is required at a depth of 2.5 μm. 0.05 This hardness can be achieved.

[0036] The nitride layer formed on the surface of a zirconium-containing group IV metal during the nitriding process can be retained or removed during the diffusion process. However, if the component is a titanium-based alloy that does not contain titanium or zirconium, the component will retain the Ti2N surface nitride layer regardless of the second temperature, but not the TiN layer. Generally, the nitride layer can be retained by performing the diffusion process at a lower second temperature. For example, the nitride layer can be retained by performing the diffusion process at a second temperature that is significantly lower than the first temperature, for example, the first temperature being 650°C to 700°C and the second temperature being 400°C to 600°C. Therefore, if the nitride layer is to be removed, the second temperature must be at least 600°C, and if the nitride layer is to be retained, the second temperature must be at most 600°C. If the nitride layer is to be removed, the hydrogen removal time must be sufficient to ensure the removal of the nitride layer, and if the nitride layer is to be retained, the hydrogen removal time must be limited to prevent the removal of the nitride layer. Generally, it is possible to stop the diffusion process by, for example, lowering the temperature, inspect the progress of removal or retention of the nitride layer, and then restart the diffusion process.

[0037] While it is possible to remove the nitride layer at temperatures below 600°C, this generally involves performing the hydrogen removal process for an extended period and monitoring the status of nitride layer removal. Therefore, in certain cases, the process of removing hydrogen from the hydrogen-containing diffusion zone involves selecting a second temperature between 400°C and 600°C, and at the selected second temperature, for up to 10°C over a sufficient hydrogen removal time to ensure the removal of the nitride layer, except for Ti2N, if the group IV metal is titanium or a titanium alloy that does not contain zirconium. -4 The process includes removing hydrogen from the hydrogen-containing diffusion zone at a partial pressure of H2 in mbar (pH2). The removal of the nitride layer may be confirmed by a preferred method, such as X-ray diffraction (XRD) analysis. Generally, the nitride layer can be removed with a hydrogen removal time of at least 48 hours when the second temperature is 500°C to 550°C, or with a hydrogen removal time of at least 24 hours when the second temperature is 550°C to 600°C. The step of removing hydrogen from the hydrogen-containing diffusion zone may also include, for example, monitoring the presence of the nitride layer by XRD analysis.

[0038] Particularly preferred combinations of a second temperature and hydrogen removal time are 600°C to 650°C for at least 4 hours (e.g., up to 200 hours); 650°C to 700°C for at least 4 hours (e.g., up to 100 hours); and 700°C to 750°C for at least 2 hours (e.g., up to 50 hours).

[0039] The most preferred combination of conditions in the nitriding and hydrogen removal processes is: for the first temperature and nitriding time in the nitriding process, 580°C to 700°C and at least 12 hours (e.g., at least 16 hours or at least 20 hours), up to a maximum of 100 hours; and for the second temperature and hydrogen removal time, 650°C to 700°C and at least 4 hours (e.g., up to a maximum of 100 hours). When the first temperature is 580°C to 700°C and the nitriding time is 16 to 100 hours, a sufficient amount of nitrogen is dissolved in the group IV metal; when the second temperature is 650°C to 700°C and the hydrogen removal time is 4 to 100 hours, the nitride layer is removed while retaining the hardening obtained from the nitrogen in the solid solution in the nitrogen diffusion zone, except for Ti2N if the group IV metal is titanium or a titanium alloy that does not contain zirconium.

[0040] In other aspects, the present invention relates to components that can be obtained by the method of the present invention. Accordingly, in another aspect, the present invention relates to components of zirconium or a group IV metal alloy containing at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%) of zirconium, wherein the core hardness and the microhardness from the surface of the component are 50 HV from the core hardness. 0.005 It has a nitrogen-containing diffusion zone that extends to a depth from the surface equal to the sum of the two values, and the hardness at a depth of 2.5 μm from the surface is 1000 HV. 0.005 ~1500HV 0.005 This concerns a component that does not contain a nitride layer, but it is conceivable that a nitride layer could be retained, for example, if hydrogen removal is performed at a maximum temperature of 600°C.

[0041] Components can also be obtained that further contain a nitride layer on the surface. The nitride layer contains ZrN and, if titanium is present in the alloy, also contains TiN. In particular, since ZrN and TiN can coexist and are isomorphic, the nitride layer can be written as (Ti,Zr)N. When the nitride layer is retained in the component, the surface hardness of the component is generally higher than when the nitride layer is removed, but the diffusion zone near the surface has the highest nitrogen content and a hardness of at least 1000 HV. 0.05 Generally, the surface hardness of a component having a (Ti,Zr)N layer is 1000 HV. 0.005 ~2000HV 0.005 That is the case.

[0042] In these component examples, the diffusion zone does not contain interstitial oxygen or dissolved oxygen beyond naturally unavoidable amounts of oxygen, and the hardness of the diffusion zone is due to the dissolved nitrogen content. In particular, the component may not contain substantially any interstitial oxygen or dissolved oxygen. Without being bound by theory, the inventors believe there is a direct correlation between the nitrogen content in the diffusion zone and the hardness of the diffusion zone, with hardness increasing across the diffusion zone from the core of the zirconium or a Group IV metal alloy containing at least 2 wt% (e.g., at least 3 wt% or at least 5 wt%) zirconium to the surface of the component. The component is more preferably oxide-free, except for a nanometer-scale oxide layer that naturally forms on the surface of the Group IV metal in contact with air, and is therefore substantially oxide-free. However, in other examples, the diffusion zone of the component also contains interstitial oxygen. Interstitial oxygen may be provided by treating the workpiece to dissolve oxygen in the zirconium or a Group IV metal alloy containing at least 2 wt% zirconium prior to treatment in the nitriding process.

[0043] The components are preferably derived from a titanium-based alloy containing 10 wt% to 20 wt% zirconium, although the titanium-based alloy may also contain additional elements. Typical group IV metals and alloys include Zr702 zirconium, Ti13Nb13Zr, and Ti15Zr.

[0044] In another example, a Group IV metal alloy is a titanium-based alloy or pure titanium that does not contain zirconium. Typical Group IV metals and Group IV metal alloys are commercially pure (CP) titanium, e.g., Grade 2 or Grade 4, Grade 5 titanium, also known as Ti6Al4V, or Ti6Al4V ELI, also known as Grade 23. When a titanium-based alloy or pure titanium that does not contain zirconium is treated with a nitriding process, the nitriding process imparts a golden color to the alloy or titanium, which is representative of TiN. Treatment with a diffusion process removes the golden color, and the treated workpiece of the titanium-based alloy or pure titanium that does not contain zirconium returns to its original appearance, including the metallic luster of the workpiece before nitriding. Surprisingly, the inventors have found that the golden nitride layer contains both TiN and Ti2N, but the diffusion process removes TiN without removing Ti2N, and as a result, this method provides a high-hardness Ti2N surface nitride layer (see, for example, Figures 5 and 6), for example, the surface hardness of the component is 700 HV 0.005 ~2000HV 0.005 For example, 1000HV 0.005 ~1800HV 0.005 However, it is not possible to visually distinguish the component from a titanium-based alloy or pure titanium that does not contain zirconium before the nitriding process. The microhardness at a depth of 2.5 μm from the surface of the component is typically 700 HV. 0.005 ~1200HV 0.005 The inventors, in particular, found that a Ti2N layer was present on the surface of the workpiece after treatment, based on XRD analysis of the workpiece. A representative XRD plot of the workpiece after treatment is shown in Figure 6. The XRD plot can be compared, for example, with the XRD plot obtained after nitriding treatment without a diffusion step, as shown in Figure 5. The comparison between Figure 6 and Figure 5 shows that Ti2N is present after both processes, but after the diffusion step, the XRD plot no longer shows a TiN peak. The Ti2N layer is hard enough for the workpiece to be scratch-resistant, and its surface hardness is, for example, at least 1000 HV. 0.005 Therefore, the present invention provides scratch-resistant workpieces of titanium or titanium alloys having metallic luster.

[0045] In another aspect, the present invention relates to a titanium-based alloy component that does not contain titanium or zirconium, wherein the core hardness and the surface hardness of the component are 50 HV from the core hardness. 0.005 The present invention relates to a component having a surface with a Ti2N layer, particularly a Ti2N surface nitride layer, which has a nitrogen-containing diffusion zone extending to a depth from the surface equal to the sum of the above. The surface hardness of the component is 700 HV 0.005 ~2000HV 0.005 The Ti2N layer is nitrided using NH3 in a nitriding process at a first temperature of 450°C to 750°C for at least 12 hours, for example, at least 16 hours, and then at a second temperature of 600°C to 750°C and up to 10 -4 This can be obtained by continuing the diffusion process for at least 4 hours of hydrogen removal time at a partial pressure of H2 in mbar. The surface is preferably TiN-free. In particular, both Ti2N and TiN are distinguishable by XRD, and in certain examples, the component contains XRD-distinguishable Ti2N. In other examples, the component does not contain XRD-distinguishable TiN. Most preferably, the component contains XRD-distinguishable Ti2N but does not contain TiN.

[0046] It is even more preferable that the component does not exhibit a golden color and has a metallic luster. For example, the component may have a mirror-polished appearance defined as a surface with an arithmetic mean deviation (Ra) roughness of less than 0.1 μm in accordance with the ISO 1302:2002 standard.

[0047] In the case of titanium-based alloy components that do not contain titanium or zirconium, the diffusion zone does not contain interstitial oxygen or dissolved oxygen, and in particular, the component may not contain substantially any interstitial oxygen or dissolved oxygen, and the hardness of the diffusion zone is due to the nitrogen content. Without being bound by theory, the inventors believe there is a direct correlation between the nitrogen content in the diffusion zone and the hardness of the diffusion zone, such that the hardness increases from the core of the titanium-based alloy that does not contain titanium or zirconium to the surface of the component. However, in another example, the diffusion zone of the component also contains interstitial oxygen. Interstitial oxygen may be provided by treating the workpiece to dissolve oxygen in the titanium-based alloy that does not contain titanium or zirconium, either before the nitriding process or after the diffusion process.

[0048] The component has a Ti2N surface layer that provides scratch resistance to the surface. Generally, the surface hardness is at least 1000 HV. 0.025 In this case, it is considered scratch-resistant. The surface hardness of the component is, for example, 700 HV. 0.005 ~2000HV 0.005 For example, 1000HV 0.005 ~1800HV 0.005 This is also acceptable. The surface hardness of the component is 1000 HV. 0.005 ~1800HV 0.005 Therefore, mirror polishing in accordance with the ISO 1302:2002 standard is particularly preferred.

[0049] Any aspect of the present invention may be used in any aspect of the present invention, and any advantages of a particular aspect may apply similarly when one aspect is used in a particular aspect.

[0050] The present invention will be described in more detail below, with reference to schematic diagrams and with the help of examples. [Brief explanation of the drawing]

[0051] [Figure 1] Figure 1 shows pH2 as a function of the NH3:N2 ratio at different total pressures. [Figure 2] Figure 2 shows the hardness profile of Ti15Zr cured using NH3. [Figure 3] Figure 3 shows the hardness profile of Ti15Zr cured according to the method of the present invention. [Figure 4] Figure 4 shows the hardness profile of Ti15Zr cured according to the method of the present invention. [Figure 5] Figure 5 shows the XRD analysis of Ti6Al4V cured using NH3. [Figure 6] Figure 6 shows the XRD analysis of Ti6Al4V cured according to the method of the present invention. [Figure 7] Figure 7 shows the hardness profile of titanium hardened according to the method of the present invention. [Figure 8] Figure 8 shows a microscopic image of a cross-section of titanium hardened using NH3. [Figure 9] Figure 9 shows a microscopic image of a cross-section of titanium hardened according to the method of the present invention. [Modes for carrying out the invention]

[0052] Detailed explanation The present invention is not limited to the embodiments shown in the drawings. Therefore, if reference numerals follow features mentioned in the claims, please understand that such numerals are included solely for the purpose of improving the clarity of the claims and are not intended to limit the claims in any way.

[0053] The present invention relates to a method for surface hardening of Group IV metals or Group IV metal alloys, components of Zirconium or Group IV metal alloys containing at least 2 wt% Zirconium, and components of Titanium or titanium-based alloys that do not contain Zirconium. These components can be obtained by the method of the present invention.

[0054] In this specification, “Group IV metal” is any metal selected from Group Titanium of the periodic table, or an alloy containing at least 50% of a metal from Group Titanium. Thus, “titanium alloy” is an alloy containing at least 50%(a / a) titanium, and similarly, “zirconium alloy” is an alloy containing at least 50%(a / a) zirconium. For the methods and components of the present invention, an alloy in which the combined total of titanium and zirconium is at least 50%(a / a) is considered suitable. Similarly, any alloy in which the combined total of titanium, zirconium, and hafnium is at least 50%(a / a) is also suitable for the present invention and may contain hafnium, which is a member of Group IV of the periodic table.

[0055] The alloys of the present invention may contain other suitable elements, and in this specification, “alloying element” may refer to a metallic component or element in the alloy, or any constituent component in the alloy. Titanium and zirconium alloys are well known to those skilled in the art. Alloys of Group IV metals may contain metals from other groups of the periodic table, such as aluminum or niobium. A typical niobium-containing alloy is Ti13Nb13Zr. An aluminum-containing alloy is Ti6Al4V (Grade 5), which exists as Ti6Al4V ELI, a “very low penetration” (ELI) version commonly referred to as Grade 23. Further important alloys include titanium 6Al-2Sn-4Zr-6Mo, titanium 6Al-2Sn-4Zr-2Mo, Ti-3Al-8V-6Cr-4Mo-4Zr(TB9), Ti-5Al-2.5Sn (Grade 6), Ti-3Al-2.5V (Grade 9), Ti-15V-3Al-3Sn-3Cr, Ti-23Nb-0.7Ta-2Zr-1.2O (Gummetal), Ti-6Al-7Nb, Ti-15Zr-4Nb-4Ta, Ti-35Nb-7Zr-5Ta, Ti-29Nb-4.6Zr-13Ta, Ti-15Mo-5Zr-3Al, and Ti-15Mo.

[0056] Any grade of titanium containing at least about 99% (w / w) titanium is considered herein to be “pure titanium,” e.g., Grade 1 titanium, Grade 2, or Grade 4 titanium; therefore, pure titanium may contain up to about 1% (w / w) of trace elements, e.g., oxygen, carbon, nitrogen, or other metals (e.g., iron). Pure titanium may also be referred to as “commercially pure” (CP). In particular, nitrogen and carbon in the Group IV metals herein may be unavoidable impurities. Elements present as “unavoidable impurities” are considered not to affect the workpieces processed according to the methods of the present invention or the components of the present invention. Similarly, a grade of zirconium containing at least about 99% (w / w) zirconium is considered herein to be “pure zirconium.”

[0057] When percentages are used for metals or alloys, unless otherwise specified, the percentage is expressed as weight relative to the weight of the material, for example, as %(w / w). When percentages are used for atmospheres, unless otherwise specified, the percentage is expressed as volume, for example, as %(v / v). Similarly, unless otherwise specified, the composition of gas mixtures may be atomic-based and may be expressed as a percentage or in parts per million (ppm).

[0058] In this specification, hardness is generally measured according to the DIN EN ISO 6507 standard (HV). 0.005 or HV 0.025 Therefore, unless otherwise specified, the unit "HV" refers to this standard. Hardness may be measured, for example, on the cross-section of a treated Group IV metal, or it may be described in terms of the depth of measurement. Hardness measured on a cross-section may also be called "microhardness," and hardness measured on a surface may also be called "macrohardness." When hardness is measured on a surface, the hardness measurement may also be called a top-down measurement.

[0059] Generally, microhardness measurement is performed using 5g, i.e., HV. 0.005 , 25g, i.e., HV 0.025, or 50g, i.e., HV 0.05 It may be carried out with a load of . In contrast, macrohardness measurements may be carried out with much higher loads, e.g., HV 0.5 The measurement may be performed from the surface with a load of 0.50 kg, which corresponds to 5 g, and therefore the measurement represents the overall hardness of each material and any surface layers it contains. In this specification, for example, the microhardness measurement obtained on the cross-section of a component manufactured according to the method of the present invention is performed with a load of 5 g, i.e., HV 0.005 The test was conducted using a 25g load, i.e., HV. 0.025 This is obtained as a top-down measurement using [this method].

[0060] When hardness is recorded in cross-section, the measurement is considered to represent a homogeneous sample with respect to the direction of applied pressure. In contrast, when hardness is obtained from surface measurements, the measurement may represent the average of multiple different hardness values, i.e., hardness values ​​at different depths. Therefore, when surface hardness is measured under a high load, e.g., 0.50 kg, the value can be considered to represent the "average" value of both the surface and the depth from the surface. Surface hardness is preferably measured under a load of 25 g or 50 g. When surface hardness is measured under a load of 25 g, the value is 650 HV. 0.025 The value of is considered to indicate that the material is scratch-resistant. Due to the effect of nitrogen dissolving from the surface, the dissolved nitrogen content decreases from the surface towards the core of the group IV metal, and similarly, the hardness is also greatest at the surface and decreases with depth. [Examples]

[0061] Example 1 Two samples of Ti15Zr alloy were prepared and nitrided with NH3 using a Netzsch 449 thermal analyzer (furnace). The samples were heated to 690°C at 20°C / min and exposed to NH3 at ambient pressure for 20 hours. Both samples were cooled to ambient temperature, and one sample was not further processed. The other sample was then subjected to a vacuum, i.e., a total pressure of 10°C obtained using an Edwards 85 T-station turbo vacuum pump. -4 The sample was processed at 690°C for 4 hours at a bar of less than mbar.

[0062] In both samples, a golden surface was obtained during the nitriding process, but the golden color disappeared during the subsequent diffusion process. Therefore, the nitride layer was removed, and the nitrogen present in the nitride layer dissolved into the diffusion zone.

[0063] Hardness of the sample after treatment (HV 0.005 The hardness profiles are shown in Figures 2 and 3, respectively, after analysis. In Figures 2 and 3, the error bars represent one standard deviation from the mean. In all cases, the treatment resulted in a hardness of 1100 HV at 2.5 μm from the surface. 0.005 Hardness exceeding 400 HV was achieved (Figures 2 and 3). In samples treated according to the present invention, 400 HV was first achieved at a depth of approximately 50 μm. 0.005 A core hardness of less than 400HV was achieved (Figure 2). In samples where the diffusion process was not performed, the hardness was 400HV. 0.005 The value below 30 μm had already been reached (Figure 3).

[0064] This level of hardness is equivalent to the fact that zirconium-containing titanium alloys incorporate more than 10 times the amount of nitrogen compared to conventional titanium alloys that do not contain zirconium.

[0065] Furthermore, during the nitriding process, needle-shaped hydrides were formed within the grains and at the grain boundaries of the test specimen. After the diffusion process, the formation of new α-grains was observed in the bulk as a result of hydrogen removal during the diffusion process and the transformation of the needle-shaped hydrides. Therefore, the method of the present invention refines the grains of the treated metal.

[0066] Example 2 A Ti13Zr13Nb sample was prepared and nitrided with NH3 using a Netzsch 449 thermal analyzer. The sample was heated to 690°C at 20°C / min, exposed to NH3 at ambient pressure for 20 hours, and then subjected to vacuum, i.e., total pressure 10°C. -4 The sample was treated at 690°C for 4 hours at a pressure of less than mbar. After nitriding, the sample exhibited a golden color, which disappeared during the subsequent diffusion process. Therefore, the nitride layer was removed. The hardness at 2.5 μm from the surface was 1100 HV. 0.005 It exceeds 500 HV at a depth of approximately 35 μm from the surface. 0.005It was revealed from the hardness profile that the core hardness had reached less than a certain value.

[0067] Example 3 Samples of Ti15Zr were prepared and nitrided with NH3 using a Netzsch 449 thermal analyzer. The samples were heated to 690 °C at 20 °C / min and exposed to NH3 for 20 hours at ambient pressure. After that, the samples were treated in vacuum, i.e., at a total pressure of less than 10 -4 mbar for 24 hours at 550 °C. After the nitriding treatment, the samples presented a golden color, which was retained during the subsequent diffusion process. Thus, the nitride layer was retained. The hardness profile is shown in Fig. 4. The surface hardness exceeds 1200 HV 0.025 and the hardness at 2.5 μm from the surface exceeds 1100 HV 0.005 Fig. 4 shows that the error bars represent one standard deviation from the mean. The hardness profile indicates that the surface hardness of the treated samples is very high.

[0068] Example 4 Samples of Ti13Zr13Nb were prepared and nitrided with NH3 using a Netzsch 449 thermal analyzer. The samples were heated to 690 °C at 20 °C / min and exposed to NH3 for 20 hours at ambient pressure. After that, the samples were treated in vacuum, i.e., at a total pressure of less than 10 <00,00090>mbar for 24 hours at 550 °C, thus retaining the nitride layer in the diffusion process. Similarly, the treated samples turned golden during the nitriding process, and this golden color was still visible after the diffusion process. The surface hardness of the treated samples exceeds 1000 HV 0.025 and the hardness at 2.5 μm from the surface exceeds 900 HV 0.005 The core hardness reached less than 400 HV 0.005 at about 40 μm from the surface.

[0069] Example 5 Two samples of Ti6Al4V (α-β alloy) were nitrided with NH3 at 700 °C for 16 hours at ambient pressure using a Netzsch 449 thermal analyzer. By this treatment, the surface hardness reached 2000 HV <00000,094>A nitride layer exceeding [a certain value] was obtained. The nitride layer exhibited a golden color, and X-ray diffraction (XRD) analysis was performed. The XRD plot is shown in Figure 5, which confirms the presence of Ti2N and TiN.

[0070] One of the nitrided samples was subjected to a diffusion process. Specifically, the sample was placed in a vacuum, that is, at a total pressure of less than 10 -4 mbar obtained by an Edwards 85T-station turbomolecular pump, and treated at 680 °C for 16 hours. The nitride layer lost its golden color during the diffusion process. XRD analysis was performed again, and the results are shown in Figure 6. By comparing Figure 6 with Figure 5, it is proven that TiN disappeared, but Ti2N was still detected.

[0071] The sample treated according to the present invention, compared with the sample not exposed to the diffusion process (that is, with a hardness exceeding 2000 HV 0.005 ), had a hardness exceeding 1300 HV 0.005 and a reduced surface hardness. However, despite such a reduction in hardness, it was sufficient to provide scratch resistance. Furthermore, by removing the golden color from the surface, the same, much more attractive metallic appearance as in the initial state was obtained. During the redistribution of nitrogen in the diffusion process, hydrogen was removed, thereby significantly reducing the risk of hydrogen embrittlement.

[0072] Example 6 Two samples of commercially pure (CP) titanium were prepared and nitrided with NH3 using a Netzsch 449 thermal analyzer. The samples were heated to 690 °C at 20 °C / min and exposed to NH3 for 20 hours at ambient pressure. Then, one sample was treated in a vacuum, that is, at a total pressure of less than 10 -4 mbar at 690 °C for 4 hours, and the other sample was not further treated.

[0073] The nitriding process resulted in a golden surface, which disappeared during the subsequent diffusion treatment. This proved that TiN did not exist after treatment by the two-step method of the present invention.

[0074] Figure 7 shows the hardness profile of a sample treated by the method of the present invention. The surface hardness is 1200 HV. 0.005 It exceeds [a certain value], and the hardness at 2.5 μm from the surface is 800 HV. 0.005 The fact that it exceeds this value clearly indicates that the sample has been given scratch resistance. 300 HV at approximately 20 μm from the surface. 0.005 The hardness level was less than [value missing]. In Figure 7, the error bars represent one standard deviation from the mean.

[0075] Two samples were cut and their cross-sections were exposed and microscopically analyzed, as shown in Figures 8 and 9. Figure 8 clearly shows that needle-shaped hydrides are visible after the nitriding process, and Figure 9 clearly shows that the needle-shaped hydrides disappeared after the diffusion process, thus proving that hydrogen was removed during the diffusion process.

Claims

1. A method for surface hardening of Group IV metals or Group IV metal alloys, - A step of preparing a workpiece of a group IV metal or a group IV metal alloy, where the workpiece is in its final shape. - NH as a nitride species ３ In a nitride atmosphere containing NH4, a first temperature of 450°C to 750°C and 0.5 bar to 2 bar of NH4 ３ A step of nitriding the workpiece at a partial pressure for at least 12 hours to form a hydrogen-containing diffusion zone, and - A second temperature of 600°C to 750°C and a maximum of 10 －４ H of mbar ２ Partial pressure (pH) ２ ) a step of removing hydrogen from the hydrogen-containing diffusion zone over a hydrogen removal period of at least 4 hours to form a hydrogen-deficient diffusion zone, Methods that include...

2. A method for surface hardening a group IV metal or group IV metal alloy according to claim 1, wherein the nitriding atmosphere does not contain oxidizing species.

3. A method for surface hardening a group IV metal or group IV metal alloy according to claim 1 or 2, wherein the first temperature is 580°C to 700°C.

4. The total pressure in the process of removing hydrogen from the hydrogen-containing diffusion zone is a maximum of 10 －４ A method for surface hardening a group IV metal or group IV metal alloy according to any one of claims 1 to 3, wherein the hardness is mbar.

5. A method for surface hardening a group IV metal or group IV metal alloy according to any one of claims 1 to 4, wherein the group IV metal is zirconium or a group IV metal alloy containing at least 2 wt% zirconium.

6. A method for surface hardening a group IV metal or group IV metal alloy according to any one of claims 1 to 5, wherein the second temperature is 600°C to 700°C.

7. A method for surface hardening a group IV metal or group IV metal alloy according to any one of claims 1 to 6, wherein the group IV metal is a titanium-based alloy that does not contain titanium or zirconium.

8. A component of a group-IV metal alloy containing zirconium or at least 2 wt% zirconium, wherein the component has a nitrogen-containing diffusion zone extending to a depth from the surface of the component at which the microhardness is equal to the core hardness of the component plus 50 HV ０．００５ and the hardness at a depth of 2.5 μm from the surface of the component is from 1000 HV ０．００５ to 1500 HV ０．００５ where the hardness is measured according to DIN EN ISO 6507 and the component does not contain a nitride layer, the component.

9. A titanium-based alloy component that does not contain titanium or zirconium, wherein the surface hardness of the component is 700 HV ０．００５ ~2000HV ０．００５ The component has a microhardness of 50 HV compared to the core hardness of the component. ０．００５ The component has a nitrogen-containing diffusion zone extending to a depth from the surface, where the hardness is measured according to the DIN EN ISO6507 standard, and the component is Ti ２ A component having an N surface nitride layer.

10. A titanium-based alloy component according to claim 9, wherein the surface does not contain TiN, and does not contain titanium or zirconium.

11. The Ti ２ A titanium-based alloy component that does not contain titanium or zirconium, according to claim 9 or 10, wherein the N layer is identified by X-ray diffraction analysis.

12. The microhardness of the aforementioned component at a depth of 2.5 μm from the surface is 700 HV. ０．００５ ~1200HV ０．００５ A titanium-based alloy component that does not contain titanium or zirconium, as described in any one of claims 9 to 11.

13. A component of a group IV metal alloy containing zirconium or at least 2 wt% zirconium, as described in claim 8, wherein the absence of TiN is identified by X-ray diffraction analysis, or a component of a titanium-based alloy that does not contain titanium or zirconium, as described in any one of claims 9 to 12.

14. A component of a group IV metal alloy containing zirconium or at least 2 wt% zirconium, as described in claim 8 or 13, wherein the surface of the component does not contain any oxide layers other than the nanometer-scale oxide layer naturally formed on the surface of the group IV metal that comes into contact with air, or a component of a titanium-based alloy that does not contain titanium or zirconium, as described in any one of claims 9 to 13.

15. The component is a component of a Group IV metal alloy containing at least 2 wt% zirconium, as described in any one of claims 8 or 13 to 14, having a mirror-polished appearance defined as a surface with an arithmetic mean deviation (Ra) roughness of less than 0.1 μm in accordance with the ISO 1302:2002 standard, or a component of a titanium-based alloy that does not contain titanium, as described in any one of claims 9 to 14.

16. The component is a component of a group IV metal alloy containing zirconium or at least 2 wt% zirconium, as described in any one of claims 1 to 7, or a component of a titanium-based alloy that does not contain titanium or zirconium, as described in any one of claims 9 to 15.

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