JP2013087351A - Nitride metal member and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride metal member including a non-conventional novel nitride layer.SOLUTION: The nitride metal member includes a nitride layer formed in a surface part of a metal base material capable of being nitrided, and the nitride layer has nitrogen concentration at a part sufficiently deep from the outermost surface of the surface part of larger than or equivalent to that at the vicinity of the outermost surface. The nitride metal member can be obtained by irradiating a surface part of a metal base material, for example, comprising an iron and steel material, stainless steel material, titanium material or the like, with a high energy beam while the energy beam is relatively moved. The high energy beam is, for example, a near ultraviolet nanosecond pulse laser having a short wavelength in a near ultraviolet region and a pulse width in a range from 10 ps to 100 ns. Accordingly, a nitride layer having nitrogen concentration uniform down to a depth of 50 μm or more and comprising a fine nitride structure can be formed.

Description

  The present invention relates to an unconventional metal nitride member having a nitride layer and a method for manufacturing the same.

  In order to improve the strength, corrosion resistance, wear resistance and the like of the metal member, various surface modification treatments are performed. One typical surface modification treatment is nitriding treatment. As this method, a gas nitriding method, a gas soft nitriding method, a salt bath nitriding method, a discharge plasma nitriding (ion nitriding) method or the like is generally used. Non-patent documents 1 to 3 below describe discharge plasma nitridation as one of them.

  Unlike those nitriding methods, there are proposals for nitriding by irradiating a titanium-based substrate with laser light, for example, in Patent Document 1 and Non-Patent Document 4 below.

JP-A-10-72656

E.Menthe, Surf. Cort. Technol. 116-119 (1999) 199-204 Sung-Pill Hong, Surf. Coat. Technol. 122 (1999) 260-267 D.Nolan, Surf. Coat. Technol. 200 (2006) 5698-5705 Mohmad Soib Selamat, J. Materials Processing Technology 113 (2001) 509-515

  The gas nitriding method, the discharge plasma nitriding method described in Non-Patent Documents 1 to 3, and the like are methods for forming a nitrided layer by introducing nitrogen from the surface of a metal substrate and diffusing it inside. The nitride layer obtained in this way is always a nitrogen concentration gradient layer in which the nitrogen concentration decreases from the outermost surface to the inside due to the formation process. Such a nitrogen concentration gradient layer is not suitable for a wear-resistant member or the like because it gradually accelerates the exhaustion under a consumable environment and can have a short life.

  Furthermore, since the above nitriding method requires high-temperature treatment for a long time, the metal substrate is likely to be deformed, the nitrided surface roughness is deteriorated, and the nitrided structure is coarsened. In the case of the discharge plasma nitriding method, there are few such problems, but special processing equipment (such as a vacuum chamber) and processes are required, and productivity is low.

On the other hand, in Patent Document 1, a nitride layer is formed by irradiating a titanium base material in a nitrogen gas atmosphere with a continuously oscillated CO ₂ laser and reacting the sufficiently heated titanium base material with nitrogen gas. doing. Also in Non-Patent Document 4, the nitride layer is formed by the same method. According to such a nitriding method, a local nitrided layer can be formed in a short time.

  However, in these methods, the portion irradiated with the laser beam is temporarily in a semi-molten state or a molten state, and thus the nitrided layer formed by resolidification tends to have a rough surface and a coarse structure. In addition, the above-described nitriding method using laser light has limited applicable base materials, and for example, it is difficult to form an effective nitrided layer even when applied to an iron-based base material.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a metal nitride member having a new nitride layer that is completely different from the conventional one, and a method for manufacturing the metal nitride member.

  As a result of intensive studies to solve the above-mentioned problems and repeated trial and error, the present inventor irradiates the target portion of the metal substrate with a near-ultraviolet nanosecond pulse laser so that the nitrogen concentration is uniform throughout. Thus, we succeeded in obtaining a high-quality nitrided layer consisting of a fine crystal structure. By developing this result, the present invention described below has been completed.

《Metal nitride member》
(1) The metal nitride member of the present invention is a metal nitride member made of a metal base material that can be nitrided, and having a nitride layer on the surface of the metal base material. The deep layer concentration, which is the nitrogen concentration (atomic%) at the position corresponding to 90% of the nitrided layer depth as measured from the surface side, is the nitrogen concentration (atomic%) at the position corresponding to 10% of the nitrided layer depth. It is characterized by being greater than or equal to a certain shallow layer concentration.

(2) In the metal nitride member of the present invention, first, the nitrogen distribution in the nitride layer is completely different from the conventional nitride layer. The conventional nitride layer has a nitrogen distribution in which nitrogen is concentrated in the vicinity of the outermost layer, and nitrogen decreases sharply toward the inside. On the other hand, the nitride layer according to the present invention exhibits a nitrogen distribution in which nitrogen is sufficiently present not only in a shallow portion (shallow layer portion) near the outermost surface but also in a deep portion (deep layer portion) inside. That is, the nitride layer according to the present invention exhibits a nitrogen distribution in which the nitrogen concentration is substantially uniform as a whole or the shallow layer concentration is higher than the deep layer concentration, contrary to the conventional nitride layer. For this reason, the nitrided layer according to the present invention has a uniform and stable nitrided structure even in the interior, and a stable characteristic can be exhibited no matter what part of the nitrided layer is exposed. As a result, for example, it is possible to appropriately predict the lifetime of the metal nitride member due to wear of the nitride layer.

(3) In this specification, in order to clearly identify the characteristic nitrogen distribution of the nitride layer according to the present invention, the nitrogen concentration (shallow layer concentration and deep layer concentration) at a specific position of the nitride layer is intentionally deliberate. Introduced. The specific positions of the shallow layer concentration and the deep layer concentration are the positions corresponding to 10% and 90% of the nitrided layer depth, respectively, by eliminating the variation in nitrogen concentration at both ends of the nitrided layer. This is because the nitride layer can be identified stably.

  The “nitrogen concentration (atomic%)” was specified based on the analysis result of an electron beam microanalyzer (EPMA). “Nitride layer depth” is the distance (thickness) to the boundary point at which the nitrogen concentration is 0.1 atomic% as measured from the outermost surface of the nitride layer formed on the surface portion of the metal nitride member. .

  “Equivalent” between the shallow layer concentration and the deep layer concentration means that each nitrogen concentration is substantially equal at the specific position in the nitride layer described above. If stipulated strictly, “equivalent” means that the nitrogen concentration difference between the shallow layer concentration and the deep layer concentration is within 5 atomic%. Of course, if the difference in nitrogen concentration is within 3 atomic% or even within 2 atomic%, it can be said that the nitrogen distribution in the nitride layer is more uniform overall.

(4) The upper and lower limits of the nitrided layer depth according to the present invention are not particularly limited. Any range in which desired characteristics are stably expressed by the nitride layer is acceptable. A nitride layer depth of 1 μm or less may suffice, but for example, in the case of a nitride layer used for an abrasion resistant member, the nitride layer depth is preferably 1 μm or more, 10 μm or more, 50 μm or more, and more preferably 80 μm or more. On the other hand, the depth of the nitride layer is usually sufficient if it is 1000 μm or less, further 500 μm or less, even when the outermost surface (nitrided surface) of the nitride layer is polished.

<< Production Method of Metal Nitride Member >>
(1) The above-described metal nitride member can be obtained, for example, by the following production method of the present invention. That is, the method for producing a metal nitride member of the present invention irradiates a target portion of a metal base capable of nitriding in a nitrogen-containing atmosphere while moving a high energy beam relative to the target portion. The above-mentioned metal nitride member is obtained by providing an irradiation step of generating ablation in the portion to be processed and generating nitrogen in the vicinity of the portion to be processed.

(2) The reason why the above-described metal nitride member can be obtained by the production method of the present invention is not necessarily clear, but at present, it is considered as follows. When the high energy beam is appropriately applied to the processing portion of the metal base, ablation may occur in the processing portion of the metal base. By this ablation, atoms or the like constituting the metal substrate in the processing target are released by vaporization, evaporation, evaporation, scattering, or the like. The particles thus released (referred to as “emitted particles” where appropriate) can take various forms such as atoms, molecules, ions, electrons, photons, radicals, and clusters. Such emitted particles have some influence on the atmospheric gas (nitrogen or the like) in the vicinity of the portion to be processed. A reaction field consisting of a mixed state of emitted particles and active nitrogen (simply referred to as “active nitrogen”) can be generated at or near the part to be treated (referred to as “ablation part” where ablation occurs).

  The above-mentioned phenomenon occurs almost continuously one after another as the irradiation area of the high energy beam moves on the treated part of the metal substrate, and the treated part and the vicinity thereof are emitted particles and actives that generate a reaction field. A large amount of nitrogen is present.

  The active nitrogen penetrates into or near the ablation part of the metal substrate to form a nitride or nitrogen solid solution, or is combined with the released particles and filled into the ablation part. By repeating such a phenomenon, it is considered that a nitride layer in which nitrogen was sufficiently introduced deep inside was formed.

  In the manufacturing method of the present invention, unlike the conventional nitriding method, ablation is used for forming the nitride layer, so that the metal base material and the nitride layer are hardly affected by heat. Therefore, according to the production method of the present invention, the deformation of the metal substrate, the deterioration of the surface roughness, the coarsening of the structure and the like hardly occur. When ablation is used, a deep nitride layer can be formed within a short time without depending on the material of the metal substrate. Therefore, according to the manufacturing method of the present invention, even when a deep nitrided layer is formed, the degree of freedom in selecting the material of the metal substrate is very large, and it is not necessary to perform a specific nitriding treatment for a long time.

(3) The nitride layer thus formed is clearly different from a nitride layer composed of a (semi) melted solidified structure obtained by using a conventional CO ₂ laser, and has a very fine crystal structure. Specifically, the nitride layer (nitriding structure) according to the present invention may have an average crystal grain size of 10 μm or less, 1 μm or less, or even 400 nm or less. The lower limit value of the average crystal grain size is not limited, but it may be, for example, 1 nm or more, further 20 nm or more in terms of production cost, quality stabilization, and the like.

  The “average crystal grain size” in the present specification was specified as follows. First, the cross section of the structure is observed, the cross sectional shape of the recognized particles is assumed to be an ellipse, and the average value of the major axis and the minor axis is defined as one crystal grain size. Next, the simple average (arithmetic average) of crystal grain sizes calculated for five points randomly extracted from the observed cross section of the tissue was used as the average crystal grain size referred to in this specification.

(4) In the manufacturing method of the present invention, since a high energy (convergent) beam is used, local nitridation and fine nitridation that are difficult with the conventional nitriding method are possible. For example, a nitride layer having a width of 10 μm or less, 1 μm or less, or 0.5 μm or less can be formed.

  In addition, the form of the nitride layer to be formed is determined by the locus of the irradiation area of the high energy beam. Since there is no limitation on the movable range of the high energy beam, a nitride layer having a desired form can be formed regardless of the width. The portion to be processed on which the nitride layer is formed is not limited to a flat surface, and may be various curved surfaces, a curved shape (including a straight line shape), or a point shape (including a multipoint shape such as a spot shape). Furthermore, as long as a high energy beam reaches | attains, a to-be-processed part may be a hollow shape, or it may exist in the back part, and may be an undercut form.

  Further, since the nitride layer is formed on the locus of the irradiation region of the high energy beam, it can be freely adjusted to be mixed with a non-nitrided layer that is not nitrided. For example, it is easy to form a stripe-shaped or lattice-shaped surface portion in which nitrided layers and non-nitrided layers are alternately arranged. Thus, the modified structure formed in the surface part of the metal base material by coexisting the nitrided layer and the non-nitrided layer is referred to as a texture structure in this specification.

  The nitride layer and the texture structure are not limited to a two-dimensional form, but may be a three-dimensional form. By adjusting the output density, beam diameter, focus, etc. of the high energy beam, the width and depth of the nitride layer can be easily changed according to the formation position. Furthermore, it is easy to make the surface after treatment a dimple. Thus, according to the present invention, an optimum nitride layer can be freely formed according to the shape and specifications of the metal substrate. Incidentally, the conventional nitride layer depth is about several tens of μm at most, but according to the manufacturing method of the present invention, it is easy to obtain a nitride layer depth of 50 μm or more, further 100 μm or more.

(5) The “target portion” may be on the outer surface side or the inner surface side as long as it is a portion that can be irradiated with a high energy beam. Moreover, it is not necessarily restricted to the outermost surface of a metal base material, The inside is also contained in a to-be-processed part. The same applies to the “surface portion” of the metal substrate.

  The “high energy beam” is a light beam or an electron beam, and has a sufficient energy for ablating the metal substrate and a strong electric field that turns the periphery of the irradiated portion into plasma. Specifically, a laser, an electron beam, or the like.

  The “nitrogen-containing atmosphere” is an atmosphere in which nitrogen (N) serving as a nitriding source exists at a molecular level or an atomic level, and active nitrogen can be generated by ablation. Specifically, a nitrogen gas atmosphere composed of only nitrogen gas, a mixed nitrogen gas atmosphere containing nitrogen gas (for example, air atmosphere), a compound gas atmosphere containing nitrogen (N) compound (such as ammonia), and the like. The pressure and temperature of the nitrogen-containing atmosphere can be adjusted as appropriate. However, according to the manufacturing method of the present invention, a desired nitride layer can be formed even in a normal temperature and atmospheric pressure atmosphere.

<Others>
Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in various numerical values or numerical ranges described in the present specification can be newly established as a range such as “ab” as a new lower limit value or upper limit value.

Sample No. obtained by irradiating the near-ultraviolet nanolaser to the titanium alloy substrate. 11 is an SEM image showing 11 nitride layers. Specimen No. No. 11 or a sample No. obtained by irradiating a titanium alloy substrate with a CO ₂ laser. It is a graph which shows the hardness distribution in 13 surface parts. Sample No. 11 is an element mapping image obtained by EPMA analysis of 11 surface portions. Sample No. 13 is an element mapping image obtained by EPMA analysis of 13 surface portions. It is a graph which shows nitrogen concentration distribution in the surface part of each sample. Sample No. 11 is a TEM image showing 11 nitride structures. Sample No. 14 is a TEM image showing 13 nitride structures. Sample No. It is a graph which shows the X-ray-diffraction pattern of 11 nitrided layers. Specimen No. 11 is a microscopic electron diffraction image observed at three points in the nitride structure according to FIG. Sample No. obtained by irradiating the steel substrate with CO ₂ laser. 23 is an SEM image showing the structure of the surface portion of 23. Sample No. obtained by irradiating a steel substrate with a near-ultraviolet nanolaser. 21 and sample no. It is a graph which shows the hardness distribution in the surface part of 23. Sample No. obtained by irradiating a stainless steel substrate with a near-ultraviolet nanolaser or CO ₂ laser. 31 and test piece no. It is a graph which shows the hardness distribution in the surface part of 33. It is the schematic diagram which showed an example of the texture structure which consists of the nitrided layer and non-nitrided layer which were formed in the surface part of a metal base material.

  The contents described in this specification can be applied not only to the metal nitride member of the present invention but also to the manufacturing method thereof. One or two or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. At this time, the component related to the manufacturing method can be a component related to an object if understood as a product-by-process. Note that which embodiment is the best depends on the target, required performance, and the like.

《Metal nitride member》
(1) Metal base material The metal base material according to the present invention may be a pure metal or an alloy as long as it can be nitrided, regardless of the type or composition of the components. “Nitrizable” means that the introduced nitrogen can form a nitride or nitrogen solid solution, and the properties (hardness, etc.) of the metal substrate can be improved. At this time, the degree of improvement by nitrogen does not matter. The metal substrate is, for example, a steel material, a stainless steel material, a titanium material, an aluminum material, or the like. According to the production method of the present invention, the metal substrate can be nitrided without being exposed to a high temperature environment. For this reason, the metal base material which was unsuitable for the conventional nitriding method processed at high temperature is also the object of the present invention.

  The steel material may be general carbon steel or special steel containing various alloy elements. According to the production method of the present invention, a nitride layer having excellent characteristics can be formed also on the surface portion of a steel material that does not contain an alloy element. Of course, the metal substrate may contain an alloy element such as Al, Cr, or Mo that can form a hard nitride such as nitrided steel.

  The stainless steel material may be any of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and the like. In particular, austenitic stainless steels and ferritic stainless steels that do not contain carbon are not expected to be hardened by ordinary heat treatment, and are therefore significant in forming the nitride layer according to the present invention.

  On the outermost surface of the stainless steel material, a passive film composed of a dense and chemically stable chromium-based oxide having a thickness of several nanometers is usually formed. In the conventional nitriding method, introduction of nitrogen is inhibited by the passive film, and nitriding is not easy. However, according to the production method of the present invention, since ablation by irradiation with a high energy beam is used, it is easy to destroy the passive film and introduce active nitrogen into the portion to be treated. Therefore, according to the manufacturing method of the present invention, a good nitride layer can be easily and stably formed without performing any special pretreatment or atmosphere control.

  The titanium material may be pure titanium or a titanium alloy. The titanium alloy may be an α-type titanium alloy, a β-type titanium alloy, or an α-β-type titanium alloy. When the titanium material is subjected to nitriding treatment, very hard titanium nitride is formed, and a specific color is generated.

  However, since the titanium material is conventionally nitrided by heating at a high temperature of 700 ° C. or higher for a long time, the productivity is low, and the mechanical properties of the titanium material may deteriorate due to coarsening of the base material structure or the like. According to the manufacturing method of the present invention, since nitriding is performed based on ablation of the metal base and conversion of nitrogen into plasma, there is almost no thermal influence on the titanium material, and there is no conventional inconvenience. That is, according to the manufacturing method of the present invention, a metal nitride member having excellent characteristics can be produced efficiently.

(2) Nitride layer The nitride layer according to the present invention comprises a nitrogen solid solution of a metal substrate or a composite structure in which a nitride is dispersed in a metal substrate or a nitrogen solid solution. The type of nitride produced varies depending on the composition of the metal substrate, but as hard nitride, for example, Fe-based nitride (Fe ₂ N, Fe ₃ N, etc.), Ti-based nitride (Ti ₂ N, TiN) Etc.), Cr-based nitride, V-based nitride, Mo-based nitride, Al-based nitride and the like.

  The theoretical upper limit of the nitrogen concentration in the nitride layer is naturally determined by the composition of the metal substrate, the crystal structure, and the like. In other words, the nitrogen concentration in the nitride layer according to the present invention is arbitrary as long as it is within the theoretical upper limit. In the case of the production method of the present invention, since the method of introducing nitriding into the metal substrate is not the conventional surface diffusion type, a considerable amount of nitrogen can be introduced into a deep portion of the nitride layer. Generally speaking, the nitrogen concentration in the nitride layer according to the present invention is 1 to 50 atomic%, and there is no substantial difference between the shallow layer concentration and the deep layer concentration. For example, the nitrogen concentration of steel materials and stainless steel materials is 1-33 atomic%, and the nitrogen concentration of titanium materials is 1-50 atomic%. In the case of the nitride layer according to the present invention, since nitrogen is uniformly distributed, even if the average nitrogen concentration or the total amount of nitrogen is lower than that of the conventional nitride layer, it exhibits hardness higher than that of the conventional nitride layer. Can do.

  The pattern of the nitride layer formed on the surface portion of the metal substrate, the size (width, depth, etc.) of the nitride layer, and the structure size (average crystal grain size, etc.) constituting the nitride layer are as described above.

<< Production Method of Metal Nitride Member >>
(1) High energy beam The high energy beam may be of any type as long as it causes ablation at the portion to be treated of the metal substrate and active nitrogen is generated from the atmospheric gas around the ablation portion. The high energy beam is, for example, a pulse laser or an electron beam.

  In order to generate ablation, it is necessary to instantaneously apply high energy to the processing target portion of the metal substrate. That is, it is necessary to irradiate the processing target portion of the metal substrate with a high energy beam having a high energy density (fluence) exceeding the ablation threshold. As such a high energy beam, a pulse laser with a short pulse width is suitable.

  If the output, the oscillation frequency, etc. of the laser oscillation device are constant, the laser beam having a higher fluence can be irradiated to the processing portion as the pulse width is shorter. Moreover, when the pulse width is short, thermal diffusion outside the irradiation region is suppressed, and the thermal influence on the metal substrate can be suppressed while promoting ablation. Specifically, the pulse width of the pulse laser is preferably 10 ps to 100 ns, and more preferably 1 to 50 ns. If the pulse width is too large, it becomes difficult to obtain the fluence necessary for ablation, and if the pulse width is too small (for example, about 150 fs at which multiphoton absorption occurs), the form of energy application by the laser light changes, which is necessary for nitriding according to the present invention. There is a possibility that a reaction field (nitriding reaction field) is not formed.

Speaking a pulsed laser power density (suitably referred to as "laser fluence" or simply "fluence".) For ^example, when 0.3MW / cm ² ~30GW / cm 2 further is a ^3MW / cm ^{2 ~3GW} / cm 2 preferable. The fluence affects the depth of the nitride layer. If the fluence is too small, it is difficult to obtain a nitride layer having a sufficient depth. If the fluence is too large, the thermal influence on the metal substrate is increased, which is not preferable. By the way, the fluence is obtained by dividing the laser output by the laser spot area.

  In addition, the shorter the wavelength of the pulse laser, the higher the absorption rate of the laser beam by the metal substrate, thereby promoting ablation and suppressing alteration of the non-ablation part. In addition, by appropriately adjusting the wavelength of the pulse laser, a nitride layer having a sufficient nitride layer depth can be easily formed. The wavelength of such a pulse laser is preferably in the ultraviolet region (including the near ultraviolet region) shorter than the infrared region and further shorter than the visible region. Specifically, the wavelength of the pulse laser is preferably 700 nm or less, 550 nm or less, and further 380 nm or less. The wavelength of the pulse laser is preferably 190 nm or more, more preferably 320 nm or more. When the wavelength of the pulse laser is too small, the absorption of the laser by the atmospheric gas occurs, which is not preferable.

Specific examples of such a pulse laser include excimers (excitation dimers) such as F ₂ (wavelength 157 nm), ArF (wavelength 193 nm), KrF (wavelength 248 nm), XeCl (wavelength 308 nm), and XeF (wavelength 351 nm). ) Excimer laser, and YAG laser that can oscillate a short wavelength.

(2) Irradiation process An irradiation process is a process of moving the irradiation area, irradiating the surface part of a metal base material with a high energy beam according to the form of the desired nitrided layer.

  When a pulsed laser is used as the high energy beam, a continuous nitride layer is easily formed stably if the irradiation regions of the adjacent pulsed light beams are partially overlapped (overlapped). The ratio of overlapping the pulse wave irradiation area (pulse wrap ratio) is the oscillation frequency of the pulse laser, the relative movement speed with respect to the processing target (referred to as “scanning speed” as appropriate), and the size of the irradiation area on the top surface of the processing target. (Or the focal position of the pulse laser) or the like. The formation of the nitrided layer and the nitrided structure depend on the characteristics of the pulse laser described above, and therefore it is difficult to specify the pulse wrap rate uniformly. For example, it is 10 to 99.9%, 20 to 95%, or 50 to 90. % Is preferable. If the pulse wrap ratio is too small, it is difficult to form a nitride layer, which tends to be a removal process. If the pulse wrap ratio is excessive, it is difficult to improve the efficiency of nitriding treatment and homogenize the nitrided structure.

This pulse wrap rate is calculated by (r / d) × 100 (%) (d: beam diameter, r: overlap diameter of adjacent pulse waves). Here, the beam diameter (d) is a width (diameter) when the beam intensity is 1 / e ² level of the peak intensity value measured on a plane orthogonal to the laser axis. The overlapping diameter (r) of adjacent pulse waves is dR (R: distance between the centers of adjacent beams).

  The oscillation frequency, scanning speed, focus position, and the like are adjusted based on the pulse wrap ratio. An example is as follows. The oscillation frequency is preferably 1 to 100 kHz, more preferably 10 to 50 kHz, for example. If the oscillation frequency is too low, the scanning speed must be lowered, and the efficiency of the nitriding process cannot be achieved. If the oscillation frequency is excessive, the laser fluence generally decreases, and it becomes difficult to form a uniform nitride layer.

  The scanning speed is preferably 0.1 to 100 mm / s, more preferably 1 to 10 mm / s, for example. If the scanning speed is too low, the efficiency of the nitriding process cannot be improved, and if the scanning speed is too high, it becomes difficult to form a uniform nitrided layer, as in the case where the correlated oscillation frequency is too high.

  The irradiation range of each pulse light varies depending on the focal position of the pulse laser. The focal position may be on the outermost surface of the portion to be processed of the metal substrate or may be shifted from the outermost surface. However, the fluence at the irradiated portion decreases as the focal position deviates from the pulse laser irradiated portion (the outermost surface portion of the processing target portion), affecting the stability of the nitriding treatment, the nitrided layer depth, etc. in the vicinity of the irradiated portion. . This tendency is more conspicuous as the laser is condensed to form a fine spot diameter at the irradiated portion.

(3) Atmosphere The atmosphere in which the irradiation step is performed may be a nitrogen-containing atmosphere in which active nitrogen can be generated by ablation when irradiated with a high energy beam as described above. Such an atmosphere is appropriately selected according to the type of the high energy beam.

  The irradiation step may be performed in a sealed atmosphere such as a chamber, but may be performed in an open atmosphere. If a laser is used as the high energy beam, it is possible even in an air atmosphere at room temperature and pressure, which is an open atmosphere. However, in order to avoid the inclusion of impurities, etc., it is preferable to carry out the process while allowing the specific gas to flow into the portion to be processed. For example, nitrogen gas or the like may be sprayed from above or from the side of the processing target. By adjusting the gas blowing direction, it is possible to suppress the debris caused by ablation. For example, by making the blowing direction coaxial with the optical axis of the high energy beam, the controllability of the nitrogen-containing atmosphere can be increased and the homogeneity of the nitride layer can be improved.

<Application>
The use of the metal nitride member of the present invention is not limited. The surface portion having the nitride layer according to the present invention has high strength and high toughness, and also has a small surface roughness, and can stably exhibit various excellent properties (abrasion resistance, corrosion resistance, electrical properties, etc.). . Therefore, the metal nitride member of the present invention is suitable for, for example, wear-resistant members such as automobile parts, corrosion-resistant members such as turbochargers and turbines, and members for electrical equipment such as semiconductor insulation and heat dissipation substrates.

Example 1: Titanium-based substrate
<Production of sample>
(1) Metal base material A titanium alloy base material made of Ti-6 mass% Al-4 mass% V (α-β type titanium alloy), which is a typical commercially available titanium material, was prepared. The base material size is basically 15.7 × 6.5 × 10.0 mm. However, when a CO ₂ laser is used, the base material size is 100 × 100 × in order to secure the heat capacity and reduce the thermal influence. It was 5 mm.

(2) High energy beam As a high energy beam, a pulse laser having a wavelength in the near ultraviolet region (190 to 400 nm, particularly 320 to 400 nm) and a pulse width of nanosecond level (this laser is simply referred to as “near ultraviolet nano” laser). A pulse laser with a wavelength in the near infrared region (800-2500 nm) and a pulse width of nanosecond level (this laser is simply called “near infrared nano” laser) and a laser with a wavelength in the infrared region are continuously used. A CO ₂ laser (Continuous Wave Laser) that outputs to the above was prepared. Specific laser specifications are shown in Table 1. Note that the near-infrared nanolaser is a fundamental wave of a solid YAG laser, and the near-ultraviolet nanolaser is a triple wave thereof.

(3) Irradiation process Each laser beam was irradiated while blowing nitrogen gas to the to-be-processed part of a titanium alloy base material. At this time, the oscillation frequency of the laser, the relative movement speed (scanning speed) of the laser with respect to the processing target, the focal position of the laser, and the output and output density of the laser (laser fluence) are also shown in Table 1. Since the focal position is the outermost surface of the processing target, the defocusing distance is 0 μm. The blowing of nitrogen gas, the parallel side to the portion to be processed in the case of near-ultraviolet Nanoreza and Kin'akagai Nanoreza, in the case of CO ₂ laser was carried out from above along the optical axis.

Irradiation of the near-ultraviolet nanolaser and near-infrared nanolaser had a pulse wrap rate of 85%. The pulse wrap rate was calculated by the method described above. In addition, the locus of the irradiation area of each laser beam on the surface of the processed portion was a parallel straight line with an interval of 20 μm. Thus, each sample (Sample Nos. 11 and 12 shown in Table 2) subjected to the irradiation step was obtained. In the case of a CO ₂ laser, the modified region was 450 μm (beam diameter: 200 μm), and the locus of the irradiated region was a parallel straight line with an interval of 400 μm (Sample No. 13).

<Evaluation of sample>
Table 2 summarizes the presence and characteristics of nitriding in each sample. Hereinafter, they will be described in detail.

(1) Presence or absence of nitriding modification Sample No. irradiated with near-ultraviolet nanolaser 11 and a sample No. irradiated with a CO ₂ laser. A nitrided layer was observed in the portion (surface portion) to be treated with No. 13. On the other hand, the sample No. irradiated with the near infrared nanolaser. No nitride layer was observed on the surface portion of 12.

  As an example, sample no. FIG. 1 shows a state in which a cross section of the surface portion of 11 is observed with a scanning electron microscope (SEM). As is clear from FIG. In the case of No. 11, nitriding is carried out to a considerable depth on the surface portion, and it can be seen that the nitrided structure is also homogeneous and fine.

Sample No. 11, the depth of the nitrided layer was as deep as 100 μm as shown in Table 2, and the minimum width of the nitrided layer formed per laser irradiation process was about 5 μm. On the other hand, sample No. In the case of No. 13, the depth of the nitrided layer was as deep as 130 μm, but the minimum width of the nitrided layer formed per laser irradiation process was about 450 μm. Incidentally, the spot diameter of the near-ultraviolet nanolaser was 0.7 μm, and the spot diameter of the multimode CO ₂ laser used in this example was 200 μm (catalog value).

(2) Hardness The Vickers hardness of the surface portion of each sample on which the nitride layer was formed was measured at depth positions of 15 μm, 30 μm, and 45 μm from the outermost surface. The hardness distribution in the depth direction based on these measurement results is shown in FIG. Table 2 also shows the average hardness obtained by arithmetically averaging the hardness at each position in the nitride layer. As is clear from FIG. 11 shows that hardness exceeding 1000 Hv is uniformly obtained deep inside.

  On the other hand, sample No. In the case of 13, the hardness on the outermost surface side and the average hardness are high, but the hardness deep inside is abruptly decreased, and the variation in hardness is large. Incidentally, the base material (fabric) hardness of the titanium alloy base material is 350 Hv.

(3) Nitrogen concentration Sample No. 11 and sample no. The results (element mapping) of 13 surface portions analyzed by an electron beam microanalyzer (EPMA) are shown in FIGS. 3A and 3B, respectively. Moreover, the nitrogen concentration distribution in the surface part obtained from the quantitative analysis result based on EPMA is shown in FIG. The nitrogen concentration at this time was measured at a position where the depth from the outermost surface was 15 μm, 35 μm and 55 μm. The average nitrogen concentration obtained by arithmetically averaging these nitrogen concentrations is also shown in Table 2.

  Sample No. 11 shows that nitrogen is uniformly distributed from the outermost surface to a depth of about 50 μm. On the other hand, sample No. In the case of 13, the average nitrogen concentration was large, but the distribution of nitrogen concentration was non-uniform, which fluctuated greatly depending on the position.

(4) Nitrided structure Sample No. 11 and sample no. The results of observation of the cross section of 13 surface portions with a transmission electron microscope (TEM) are shown in FIGS. 5A and 5B, respectively.

  Sample No. In the case of 11, the crystal grain (portion surrounded by the thick black line in FIG. 5A) was fine, and the average crystal grain size was 150 nm. As described above, although the average nitrogen concentration was small, the sample No. 1 had sufficient hardness overall. This is probably because the nitride structure of 11 is fine as a whole. The average crystal grain size is a value obtained by arithmetically averaging the major axis and the uniaxial axis of each crystal grain appearing in the field of view of the TEM image as described above.

On the other hand, sample No. In the case of 13, it was found that a large number of needle-like crystals (portion surrounded by black thick lines in FIG. 5B) having an average length of 5.7 μm and an average width of about 0.8 μm were crystallized (or precipitated). The reason why such a structure was observed is thought to be that the part to be treated was melted by irradiation with a CO ₂ laser and then re-solidified.

  Sample No. 11 surface portions (specifically, 10 μm from the outermost surface) were analyzed by X-ray diffraction (XRD). The results are shown in FIG. The same portion of the sample was subjected to microelectron beam diffraction measurement by TEM at three locations. The result is shown in FIG.

From these results, sample no. 11 was found to disperse nitrides such as TiN, TiN _0.26 , (AlTi) N ₂ , and TiVN ₂ . That is, it has been clarified that the surface portion is not a simple nitrogen solid solution in which nitrogen is dissolved in the base material (titanium alloy) but a composite structure in which various nitrides are finely dispersed therein. On the other hand, sample No. The nitrided structure of 13 was a rough and brittle structure, and the outermost surface was undulated so as to require post-processing (see FIG. 3B).

<< Example 2: Steel base material >>
<Production of sample>
A steel base material made of a representative steel material (JIS S45C) that was commercially available was prepared. This steel substrate was irradiated with each laser described above. In this way, samples (sample Nos. 21, 22, and 23 shown in Table 2) were obtained by irradiating the steel base with each laser. The presence or absence of nitriding and the characteristics of each sample are shown in Table 2. The base material size of this example is basically 15.7 × 6.5 × 10.0 mm. However, in the case of using a CO ₂ laser, the base material is used in order to secure the heat capacity and reduce the thermal influence. The size was φ30 × 5 mm.

<Evaluation of sample>
(1) Presence or absence of nitriding Sample No. irradiated with near-ultraviolet nanolaser As in the case of the titanium alloy base material, a fine nitride structure was observed on the surface portion 21. However, a nitrided structure was not observed on the surface of the sample irradiated with other lasers, despite being in a nitrogen atmosphere. However, the sample No. irradiated with the CO ₂ laser. A quenched structure (including an annealed structure) as shown in FIG.

(2) Hardness As in the case of Example 1, sample No. 21 and Sample No. The Vickers hardness in 23 surface parts was measured, and the hardness distribution of those depth directions was shown in FIG. As is clear from FIG. In No. 21, sufficient hardness was uniformly distributed deep inside.

  On the other hand, sample No. 23, sample No. The hardness was smaller than 21, and the hardness distribution was non-uniform. Incidentally, the Vickers hardness of the steel base material itself, which is a base material, was 200 Hv.

(3) Nitrogen concentration As in the case of Example 1, sample no. The nitrogen concentration distribution in the surface portion of 21 is shown in FIG. As is clear from FIG. The nitrogen concentration of 21 was also found to be uniform deep inside.

(4) Nitrided structure As in the case of Example 1, sample No. A fine nitride structure having an average crystal grain size of 291 nm was formed on the surface portion 21.

<< Example 3: Stainless steel base material >>
<Production of sample>
A stainless steel substrate made of a typical austenitic stainless steel (JIS SUS304) that is commercially available was prepared. This stainless steel substrate was irradiated with the lasers described above to obtain samples (Sample Nos. 31, 32 and 33 shown in Table 2). The presence or absence of nitriding and the characteristics of each sample are shown in Table 2. The base material size of this example is basically 15.7 × 6.5 × 10.0 mm. However, in the case of using a CO ₂ laser, the base material is used in order to secure the heat capacity and reduce the thermal influence. The size was 30 × 30 × 8 mm.

For reference, a sample (No. 34) obtained by discharge plasma nitriding on the same stainless steel substrate was also produced. This discharge plasma nitriding was performed in an atmosphere of N ₂ + 50% H ₂ at 500 ° C. for 1 hour.

<Evaluation of sample>
(1) Presence or absence of nitriding Sample No. irradiated with near-ultraviolet nanolaser A fine nitrided structure was observed on the surface portion 31 as in the case of a titanium alloy substrate. In addition, the sample No. No. of discharge plasma nitrided Naturally, a nitrided structure was also observed in 34. However, the surface portion of the sample irradiated with the other laser was not nitrided despite being in a nitrogen atmosphere. Since the stainless steel substrate used in this embodiment is substantially free of carbon, the sample was irradiated with CO ₂ laser No. 33 includes sample no. A hardened structure such as 23 was not produced.

(2) Hardness As in the case of Example 1, sample No. 31 and Sample No. Vickers hardness at the surface portion of 33 was measured, and the hardness distribution in the depth direction was shown in FIG. As is clear from FIG. No. 31 had sufficient hardness as deep as the outermost surface side deep inside. On the other hand, sample No. No. 33 had a hardness substantially equal to the base material (fabric) hardness of 200 Hv of the stainless steel substrate, and was not substantially cured.

(3) Nitrogen concentration As in the case of Example 1, sample no. The nitrogen concentration distribution in the surface portion of 31 is also shown in FIG. As is clear from FIG. No. 31 also had a uniform nitrogen concentration deep inside.

  On the other hand, sample No. The nitrogen concentration at the surface portion of 34 was very high at 17 atomic% in the vicinity of the outermost surface, but it suddenly decreased and became almost zero at a depth of about 7 μm at most. Thus, the nitrided layer obtained by conventional discharge plasma nitriding has become a steep graded layer with respect to the nitrogen concentration.

(4) Nitrided structure As in the case of Example 1, sample No. A fine nitride structure was observed on the surface portion 31.

Example 4
The wear resistance of a metal nitride member having a nitride layer obtained by irradiation with a near-ultraviolet nanolaser was evaluated as follows.

<Production of test piece>
Three block-shaped test pieces made of the titanium material prepared in Example 1 were prepared. One of them was left untreated (test piece No. 110). In the remaining two, as in Example 1, a nitride layer was formed by irradiation with a near-ultraviolet nanolaser. However, one of them was formed with a nitrided layer over the entire surface (test piece No. 111), and the other was formed with a striped nitride layer with a pitch of 20 μm (test piece No. 112). That is, test piece No. In 112, a texture structure in which a non-nitrided layer and a nitrided layer coexist was formed.

<Test method>
Each specimen was subjected to a block on ring test. The block-on-ring test is a test method in which the sliding surface of each test piece (block) is pressed against the cylindrical outer peripheral surface of the rotating ring to evaluate the wear condition of the test piece (see ASTM standard G77-05). . Specifically, under the lubrication of non-Mo engine oil, the rotation speed was 164 rpm, the pressing load was 4.4 N, the test time was 30 minutes, and the test temperature was 80 ° C.

<Evaluation>
The test results of each test piece are shown in Table 3. Specimen No. In 110, since the sliding surface is untreated, both the wear width and the wear depth are large. On the other hand, test piece No. 111 and no. It was confirmed that No. 112 had a very small wear width and wear depth and exhibited high wear resistance. Moreover, the test piece No. 111 and test piece no. From the result of 112, it was confirmed that excellent wear resistance was exhibited even when the form of the nitrided layer was different, that is, even when the surface portion of the metal substrate had a textured structure.

  Thereby, when using the metal nitride member of this invention as an abrasion-resistant member, it turned out that it is not necessary to form a nitride layer in the whole sliding surface. That is, it has been clarified that the form of the nitrided layer or nitrided structure can be appropriately selected in consideration of the specifications and productivity of the wear resistant member.

<Others>
In the test piece described above, a nitride layer with a pitch of 20 μm was formed. However, even when a nitride layer with a pitch of 40 μm or a nitride layer with a pitch of 80 μm is formed, wear resistance equivalent to that described above can be obtained. Has been confirmed.

  In all of the above-described embodiments, the irradiation process is performed only once on the target portion. However, the irradiation process may be repeated a plurality of times. By increasing the number of irradiation steps, the nitrogen concentration in the portion to be processed can be further increased. However, according to the manufacturing method of the present invention, a nitride layer having a uniform and sufficient depth can be efficiently formed even in a single irradiation step.

Claims (9)

A metal nitride member comprising a metal substrate capable of nitriding and having a nitride layer on the surface portion of the metal substrate,
The nitride layer has a nitrogen concentration (atomic%) at a position corresponding to 90% of the nitrided layer depth measured from the outermost surface side of the metal substrate, and the nitrided layer depth is 10% of the nitrided layer depth. A metal nitride member characterized by being greater than or equal to a shallow layer concentration which is a nitrogen concentration (atomic%) at a corresponding position.   The metal nitride member according to claim 1, wherein the nitride layer has a concentration difference between the deep layer concentration and the shallow layer concentration within 5 atomic%.   The metal nitride member according to claim 1, wherein the nitride layer is formed of a nitride structure having an average crystal grain size of 10 μm or less.   4. The metal nitride member according to claim 1, wherein the metal substrate is made of a steel material, a stainless steel material, or a titanium material.   The metal nitride member according to any one of claims 1 to 4, wherein the surface portion of the metal base material has a texture structure in which the nitrided layer and the non-nitrided non-nitrided layer coexist. By irradiating the target portion of the nitridable metal substrate in a nitrogen-containing atmosphere while moving the high energy beam relative to the target portion, ablation occurs in the target portion and the target portion is irradiated. Provided with an irradiation process to generate plasma nitrogen in the vicinity of the processing unit,
A method for producing a metal nitride member, wherein the metal nitride member according to claim 1 is obtained.   The method for manufacturing a metal nitride member according to claim 6, wherein the high energy beam is a pulse laser having a wavelength of 700 nm or less.   The method of manufacturing a metal nitride member according to claim 7, wherein the irradiation step is a step of irradiating the portion to be processed with the pulsed laser while partially overlapping irradiation regions with pulsed light oscillating adjacently.   The method of manufacturing a metal nitride member according to claim 8, wherein the irradiation step has a pulse wrap ratio of 10 to 90%, which is a ratio at which the irradiation region of the pulsed light overlaps.