Nitride film forming device and nitride film forming method

Abstract

To provide a nitride film forming device and a nitride film forming method that can form a nitride film selectively on the surface of a metal by a simple technique.SOLUTION: A nitride film forming device 1 is to form a nitride film on the surface of a metal material. The nitride film forming device 1 has a pulsed laser light source 11 that repeatedly emits pulsed laser light with its energy density per pulse set so that the pulsed laser light emitted onto the metal material surface generates plasma in the air around the metal material surface, to topically melt the metal material surface and generate activated nitrogen in the air. The nitride film forming device 1 may include a focusing optical system 12 that is provided on the emission side of the pulsed laser light source 11 and focuses the pulsed laser light emitted from the pulsed laser light source 11 to the metal material surface, to generate plasma in the air around the metal material surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitride film forming apparatus and a nitride film forming method. [Background technology]

[0002] Metal materials with a nitride film formed on their surface are known to be excellent in wear resistance and corrosion resistance, making them suitable for machine parts. Gas nitriding, which involves heating titanium material in an ammonia atmosphere, and plasma nitriding, which utilizes glow discharge, are used to form the nitride film. However, these methods form a nitride film over the entire surface of the metal material; therefore, there is a need for a method that selectively forms a nitride film on only a portion of the metal material's surface. For example, Patent Document 1 discloses a method for selectively forming a nitride film on the laser-irradiated portion of a titanium material's surface by irradiating it with a laser while nitrogen gas is blown onto the titanium material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-212395 [Overview of the project] [Problems that the invention aims to solve]

[0004] The method described in Patent Document 1 requires the prior preparation of gas blowing equipment and a large amount of nitrogen gas because nitrogen gas is blown during the formation of the nitride film, making it unsuitable for mass production of metal parts with nitride films. For this reason, there is a need for a method that can selectively form a nitride film on a metal surface without blowing nitrogen gas. This problem exists not only when forming a nitride film on a titanium material surface, but also when forming a nitride film on the surface of other metal materials.

[0005] This invention is based on the above background and aims to provide a nitride film forming apparatus and a nitride film forming method that can selectively form a nitride film on a metal surface using a simple method. [Means for solving the problem]

[0006] To achieve the above objective, the nitride film forming apparatus according to the first aspect of the present invention is A nitride film forming apparatus for forming a nitride film on the surface of a metal material, The system includes a pulsed laser light source that repeatedly emits pulsed laser light, the energy density per pulse set such that the pulsed laser light irradiated onto the surface of the metal material generates plasma in the atmosphere surrounding the surface of the metal material, thereby locally melting the surface of the metal material and generating activated nitrogen in the atmosphere.

[0007] The nitride film forming apparatus may further include a focusing optical system provided on the output side of the pulsed laser light source, which generates plasma in the atmosphere surrounding the surface of the metal material by focusing the pulsed laser light emitted from the pulsed laser light source onto the surface of the metal material.

[0008] The nitride film forming apparatus may further include a holding means provided on the output side of the focusing optical system, which holds the metal material such that the surface of the metal material is positioned at the focal point of the laser beam focused by the focusing optical system.

[0009] The holding means is a moving stage that moves the metal material relative to the focusing optical system, The nitride film forming apparatus may further include control means for controlling the movement of the moving stage so that the pulsed laser light irradiated onto the metal material surface follows a predetermined trajectory.

[0010] The nitride coating forming apparatus is A robotic arm that movably supports the pulsed laser light source and the focusing optical system, Control means for controlling the operation of the robot arm so that the pulsed laser light irradiated on the surface of the metal material follows a predetermined locus may be further provided.

[0011] The energy density per pulse of the pulsed laser light irradiated on the surface of the metal material may be within the range of 1000 J / mm 2 ~�000J / mm 2 and.

[0012] The nitride film forming apparatus A pair of electrodes arranged so as to sandwich the irradiation path of the pulsed laser light emitted from the pulsed laser light source, A voltage source that is connected to each of the pair of electrodes and generates an electric field between the pair of electrodes to increase the luminance of the plasma generated when the pulsed laser light emitted from the pulsed laser light source irradiates the surface of the metal material may be further provided.

[0013] The metal material may be any one of a titanium material, a steel material, an aluminum material, a niobium material, and a zirconium material.

[0014] In order to achieve the above object, a nitride film forming method according to a second aspect of the present invention A nitride film forming method for forming a nitride film on the surface of a metal material, A step of repeatedly emitting pulsed laser light whose energy density per pulse is set so that the pulsed laser light irradiated on the surface of the metal material generates plasma in the atmosphere around the surface of the metal material, locally melting the surface of the metal material, and generating activated nitrogen in the atmosphere.

Effects of the Invention

[0015] According to the present invention, a nitride film can be formed on the surface of a metal material simply by irradiating pulsed laser light even in the atmosphere. Therefore, a nitride film forming apparatus and a nitride film forming method capable of selectively forming a nitride film on a metal surface by a simple method can be provided.

Brief Description of the Drawings

[0016] [Figure 1] It is a diagram showing the configuration of a nitride film forming apparatus according to an embodiment of the present invention. [Figure 2] It is a schematic diagram explaining the mechanism of nitriding treatment of a titanium material in the atmosphere according to an embodiment of the present invention. [Figure 3] It is a plan view showing an example of the locus of pulsed laser light according to an embodiment of the present invention. [Figure 4] It is a plan view showing another example of the locus of pulsed laser light according to an embodiment of the present invention. [Figure 5] It is a diagram showing the configuration of a nitride film forming apparatus according to the first modification of the present invention. [Figure 6] It is a diagram showing the configuration of a nitride film forming apparatus according to the second modification of the present invention. [Figure 7] It is a diagram showing the configuration of a nitride film forming apparatus according to the third modification of the present invention. [Figure 8] It is a graph showing the X-ray diffraction pattern of a titanium material irradiated with pulsed laser light having an energy density of 300 J / mm2 per pulse in Example 1. [Figure 9] It is a graph showing the X-ray diffraction pattern of a titanium material irradiated with pulsed laser light having an energy density of 5000 J / mm2 per pulse in Example 1. [Figure 10] It is a graph showing the X-ray diffraction pattern of a titanium material when the number of irradiations of pulsed laser light is 20 times in Example 2. [Figure 11] It is a graph showing the difference in the X-ray diffraction pattern of a titanium material depending on the presence or absence of condensing of pulsed laser light in Example 3. [Figure 12] It is a diagram showing a scanning electron microscope image of a titanium material in Example 3. [Figure 13] (a) and (b) are both diagrams showing scanning electron microscope images of a titanium material in Example 4. [Figure 14](a) and (b) are both figures showing laser microscope images of the titanium material in Example 4. [Modes for carrying out the invention]

[0017] Hereinafter, an apparatus and method for forming a nitride film on a metal material according to an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the case in which a nitride film is formed on the surface of a plate-shaped titanium material will be described as an example.

[0018] Figure 1 shows the configuration of a nitride film forming apparatus according to an embodiment. The nitride film forming apparatus 1 is an apparatus for forming a nitride film on the surface of a titanium material. The nitride film is not a surface layer containing nitrogen as one component, but a surface layer mainly composed of at least a nitride compound. Hereafter, a Cartesian coordinate system will be used in which the left-right direction in Figure 1 is the X-axis direction, the direction perpendicular to Figure 1 is the Y-axis direction, and the direction perpendicular to both the X-axis and Y-axis directions is the Z-axis direction (up-down direction).Hereafter, the surface of the titanium material will be assumed to be located on the XY plane.

[0019] The nitride film forming apparatus 1 comprises a pulsed laser light source 11 that emits pulsed laser light, a focusing optical system 12 that focuses the laser light from the pulsed laser light source 11, a moving stage 13 that moves the titanium material relative to the focusing optical system 12 while holding the titanium material so that the titanium material surface is positioned at the focal point where the laser light focused by the focusing optical system 12 is focused, and a control device 14 that controls the operation of the moving stage 13 so that the laser light focused on the titanium material surface traces a predetermined trajectory. The moving stage 13 and the control device 14 are connected to each other so as to be able to communicate with each other via a wired or wireless communication circuit.

[0020] The pulsed laser light source 11 is a pulsed laser light source that repeatedly oscillates pulsed laser light (pulsed laser light) at a constant frequency and pulse width. The pulsed laser light source 11 is equipped with, for example, an Nd:YAG (Yttrium Aluminum Garnet) laser. In addition, a Q switch (shutter) is provided inside the oscillator of the pulsed laser light source 11.

[0021] A signal generator 11a is connected to the pulsed laser light source 11 to generate a signal for oscillating the pulsed laser light source 11. The pulsed laser light source 11 emits laser light in pulses by switching the current from the signal generator 11a on and off. The signal generator 11a sets various parameters of the pulsed laser light emitted from the pulsed laser light source 11 based on instructions from the user. Alternatively, to obtain a pulse waveform from the pulsed laser light source 11, the laser light continuously oscillating from the laser light source may be configured to be switched on and off by a modulator or shutter.

[0022] The focusing optical system 12 focuses the pulsed laser light received from the pulsed laser light source 11 onto the surface of the titanium material. The focusing optical system 12 comprises, for example, one or more focusing lenses. The focusing lenses are, for example, convex lenses. The pulsed laser light source 11 and the focusing optical system 12 are connected to a suspension device 15 and positioned above the moving stage 13. By focusing the pulsed laser light, the focusing optical system 12 increases the energy per unit area (energy density) of the pulsed laser light at the focal point.

[0023] Figure 2 is a schematic diagram illustrating the mechanism of nitriding treatment of titanium materials in the atmosphere. Because titanium materials preferentially bond with oxygen, even when a continuous-wave laser is irradiated onto the surface of a titanium material in the atmosphere, a chemically stable oxide film is formed. On the other hand, when pulsed laser light is focused by a focusing optical system 12 and irradiated onto the surface of a titanium material, nitrogen molecules in the atmosphere near the titanium surface are incorporated into the titanium material, bond with titanium atoms, and form a nitride film on the surface of the titanium material.

[0024] In detail, when pulsed laser light, whose energy density has increased due to focusing, is irradiated onto the surface of a titanium material, the laser energy is concentrated both temporally and spatially, causing a plasma consisting of nitrogen, oxygen, and metallic material components to be locally generated in the air surrounding the irradiated area. The energy imparted from this plasma instantaneously melts the surface of the metallic material, including the pre-existing oxide film, and convection of the molten titanium occurs. This convection preferentially incorporates activated nitrogen components from the air into the molten titanium, thus forming a nitride film on the surface of the metallic material. Note that nitride film formation can be achieved in other metallic materials through a similar mechanism.

[0025] To melt the surface of a titanium material using plasma in the atmosphere, the pulsed laser light frequency is preferably, for example, 10 Hz or less, and the pulse width is preferably a few nanoseconds, for example, in the range of 1 to 5 nanoseconds. Furthermore, when the pulse width is set to a few nanoseconds, the pulse energy density, which is the energy per pulse of the pulsed laser light, should be set to such an extent that the pulsed laser light irradiated onto the titanium material surface generates plasma in the atmosphere surrounding the titanium material surface, causing localized melting of the titanium material surface and generating activated nitrogen in the atmosphere.

[0026] The pulse energy density is at least 1000 J / mm². 2 Preferably, it is 1000 J / mm². 2 ~6000J / mm 2 It is more preferable that it be within the range of 1000 J / mm 2 ~5000 J / mm 2 It is even more preferable that the values ​​be within this range. The pulse energy density of the pulsed laser light can be determined experimentally in advance to an optimal value, taking into account the thickness of the nitride film on the titanium material. Furthermore, the frequency and pulse width of the pulsed laser light can be set based on the pulse energy density of the pulsed laser light, the beam cross-sectional area, and the moving speed of the moving stage.

[0027] Returning to Figure 1, the moving stage 13 is an example of a holding means for holding a titanium material so that the surface of the titanium material is positioned where the pulsed laser light is focused by the focusing optical system 12. The moving stage 13 holds the titanium material to be processed and moves the titanium material in the X-axis and Y-axis directions so that the pulsed laser light from the focusing optical system 12 traces a set trajectory on the surface of the titanium material.

[0028] The moving stage 13 includes a base, a first moving member that moves in the X-axis direction relative to the base, a first motor that moves the first moving member relative to the base, a second moving member that moves in the Y-axis direction relative to the first moving member, and a second motor that moves the second moving member relative to the first moving member. Both the first motor and the second motor are connected to a motor driver, and the motor driver is connected to a control device 14.

[0029] The movement path of the moving stage 13 is set considering the shape and size of the processing area on the titanium material surface where the nitride film is formed, as well as the cross-sectional shape and size of the focused pulsed laser beam. For example, the movement path of the moving stage 13 is set so that the pulsed laser beam irradiated onto the titanium material completely fills the processing area on the titanium material surface where the nitride film is formed. Below, a specific example of the trajectory of the pulsed laser beam is described, assuming that the cross-sectional shape of the pulsed laser beam is circular.

[0030] Figure 3 is a plan view showing an example of the trajectory of a pulsed laser beam according to an embodiment. In the trajectory of the pulsed laser beam in Figure 3, the focal point of the pulsed laser beam is moved in the +X direction from one end to the other of the rectangular processing area where the nitride film is formed. Next, it is moved in the -Y direction by a distance equivalent to the diameter of the pulsed laser beam. Next, it is moved in the -X direction from the other end to the first end. Next, it is moved again in the -Y direction by a distance equivalent to the diameter of the pulsed laser beam. The above steps are repeated until the trajectory fills the processing area. When moving the trajectory of the pulsed laser beam in the Y direction, it is preferable to stop the irradiation of the pulsed laser beam until the movement in the Y direction is completed.

[0031] Figure 4 is a plan view showing another example of the trajectory of a pulsed laser beam according to the embodiment. The trajectory of the pulsed laser beam in Figure 4 is such that it sequentially traces multiple circles with the same center point but different diameters in a circular processing area. When moving the pulsed laser beam radially, it is preferable to stop the irradiation of the pulsed laser beam until the radial movement is complete. In addition, in a circular processing area, the pulsed laser beam may be set to trace a spiral trajectory.

[0032] The movement speed of the moving stage 13 is set considering various characteristics of the pulsed laser light, such as pulse energy density, frequency, and pulse width, but is, for example, within the range of 0.1 mm / s to 2 mm / s. The movement of the moving stage 13 may be continuous scanning or intermittently repeated movement and stopping. For example, multiple adjacent spots may be set in the processing area, pulsed laser light may be irradiated onto one spot with the moving stage 13 stopped, and then the moving stage 13 may be moved so that pulsed laser light can be irradiated onto adjacent spots. Also, if the frequency is relatively high, the time interval between pulsed laser light irradiations becomes longer, so even if the moving stage 13 is scanned continuously, the movement of the moving stage 13 can be completed by the next irradiation timing.

[0033] The number of irradiations is the number of times the same location on the titanium material surface is irradiated with pulsed laser light, and is also the number of times a trajectory like that shown in Figure 3 or Figure 4 is drawn on the titanium material surface. The number of irradiations is arbitrarily set according to the pulse energy density of the pulsed laser light, but is preferably in the range of 1 to 20 times. When the pulse energy density is relatively high, one irradiation is preferred, and when the pulse energy density is relatively low, multiple irradiations, for example, about 5 to 10 irradiations, are preferred.

[0034] Returning to Figure 1, the control device 14 is, for example, a general-purpose computer equipped with memory and a processor. The control device 14 is an example of a control means that controls the operation of the pulse laser light source 11 and the moving stage 13 by executing a program stored in memory using the processor.

[0035] The control device 14 receives user instructions regarding the pulse energy density, frequency, pulse width, and number of pulses of the pulsed laser light, as well as the movement path and movement speed of the moving stage 13. Upon receiving user instructions, the control device 14 controls the operation of the pulsed laser light source 11 so that it oscillates with the set pulse energy density, frequency, and pulse width of the pulsed laser light. The control device 14 also controls the operation of the first and second motors of the moving stage 13 so that the moving stage 13 moves according to the set number of pulses of the pulsed laser light, as well as the movement path and movement speed of the moving stage 13. The above describes the configuration of the nitride film forming apparatus 1.

[0036] Next, the procedure for forming a nitride film on a titanium material using the nitride film forming apparatus 1 according to the embodiment will be explained.

[0037] First, the titanium material to be subjected to nitride coating is held in the moving stage 13.

[0038] Next, the user operates the control unit of the control device 14 to specify the pulse energy density, frequency, pulse width, and number of pulse laser beam irradiations of the pulsed laser beam, as well as the movement path and movement speed of the moving stage 13 (hereinafter collectively referred to as "processing conditions"). Upon receiving the user's instructions regarding the processing conditions, the control device 14 stores the information regarding the processing conditions in its memory.

[0039] Next, when the user operates the operation unit of the control device 14 to instruct the start of laser irradiation, the control device 14 irradiates pulsed laser light from the pulsed laser light source 11 and moves the moving stage 13 from the starting point of the movement path based on the processing conditions stored in the memory. At this time, the nitrided film forming apparatus 1 repeats the process of emitting pulsed laser light from the pulsed laser light source 11 at each spot on the movement path (emission process) and the process of condensing the pulsed laser light emitted in the emission process onto one spot on the surface of the titanium material (condensing process), thereby sequentially forming a nitrided film on the path on the surface of the titanium material.

[0040] Next, when the control device 14 arrives at the end point of the movement path stored in the memory, it ends the irradiation of the pulsed laser light from the pulsed laser light source 11. The above is the flow of the method for forming a nitrided film on a titanium material.

[0041] As described above, the nitrided film forming apparatus 1 according to the embodiment includes a pulsed laser light source 11 that emits pulsed laser light, and a focusing optical system 12 provided on the emission side of the pulsed laser light source 11 that focuses the pulsed laser light emitted from the pulsed laser light source 11 onto the surface of the titanium material. In addition, in the pulsed laser light source 11, the energy density per pulse is set so that the pulsed laser light generates nitrogen plasma in the air to locally melt the surface of the titanium material and generate activated nitrogen in the air. Therefore, even in the air, a nitrided film can be formed on the surface of the titanium material by concentrating laser energy temporally and spatially. Also, since a nitrided film can be formed in the air, there is no need to limit the size of the object on which the nitrided film is formed. Furthermore, since the nitrided film is formed only in the region irradiated with the pulsed laser light, a nitrided film can be selectively formed on a part of the surface of the titanium material.

[0042] Also, in the nitrided film forming apparatus 1 according to the embodiment, the energy density per pulse emitted from the pulsed laser light source 11 is preferably 1000 J / mm 2 ~6000 J / mm 2This falls within a certain range. Therefore, large deformations of the titanium material surface and a decrease in mechanical strength can be suppressed. Furthermore, when pulsed laser light is focused by the focusing optical system 12, the above energy density can be achieved with a pulsed laser light source 11 having an energy of about 100 mJ to 500 mJ per pulse. Since such a pulsed laser light source 11 can be obtained inexpensively, the manufacturing cost of the nitride film formation apparatus 1 can be reduced.

[0043] The present invention is not limited to the embodiments described above, and the following modifications are also possible.

[0044] (modified version) In the above embodiment, the nitride film forming apparatus 1 was provided with one pulsed laser light source 11 and one focusing optical system 12, but the present invention is not limited thereto. For example, by providing multiple sets of pulsed laser light sources 11 and focusing optical systems 12, a nitride film may be rapidly formed on the surface of a titanium material.

[0045] In the above embodiment, the titanium material surface was moved relative to the focused pulsed laser light by moving the moving stage 13 relative to the focusing optical system 12, but the present invention is not limited to this. For example, as shown in Figure 5, the pulsed laser light source 11 and the focusing optical system 12 may be supported at the tip of a robot arm 16, and the tip of the robot arm 16 may be moved in the X-axis direction and the Y-axis direction. In this case, the titanium material may be held by a holder 17 that does not have a moving mechanism.

[0046] According to the above modified example, the nitride film forming apparatus 1 can be placed at any position on the manufacturing line, and nitride films can be formed on parts or products in the middle of the manufacturing line. Furthermore, the nitride film forming apparatus 1 may be used to retrofit nitride films onto parts or products, or to form nitride films for the repair or reinforcement of parts or products.

[0047] In the above embodiment, the titanium material to be processed was a plate-shaped member, and the distance in the Z-axis direction between the focusing optical system 12 and the moving stage 13 was constant. However, the present invention is not limited to this. For example, if there are irregularities on the surface of the titanium material, the operation of the focusing optical system 12 or the moving stage 13 may be controlled to maintain a constant distance in the Z-axis direction between the titanium material surface and the focusing optical system 12.

[0048] Specifically, as shown in Figure 6, a distance sensor 18 may be provided to measure the distance between the focusing optical system 12 and the titanium material. Based on the signal from the distance sensor 18, the movement of the robot arm 16 may be controlled to maintain a constant distance between the surface of the titanium material held by the holder 17 and the focusing optical system 12. The specific process described above can be performed using PID (Proportional-Integral-Differential) control.

[0049] Alternatively, the moving stage 13 may be configured to move in the Z-axis direction as well, and its movement in the Z-axis direction may be controlled based on a signal from the distance sensor 18 to maintain a constant distance between the titanium material surface held by the moving stage 13 and the focusing optical system 12.

[0050] In the above embodiment, a control device 14 was connected to the signal generator 11a of the pulsed laser light source 11, and the signal generator 11a turned the current on and off based on the signal from the control device 14. However, the present invention is not limited to this. For example, the signal generator 11a may be configured to allow the user to directly operate it to set parameters such as the pulse energy density, frequency, and pulse width of the pulsed laser light.

[0051] In the above embodiment, a nitride film was formed on the surface of a plate-shaped titanium material, but the present invention is not limited thereto. The shape of the titanium material can be arbitrary, and may be, for example, box-shaped, spherical, or concave.

[0052] In the above embodiment, a nitride film was formed on a titanium material in the atmosphere, but the present invention is not limited thereto. For example, a nitride film may be formed on other metallic materials such as steel, aluminum, niobium, or zirconium using the same or equivalent method.

[0053] In the above embodiment, plasma was generated in the atmosphere simply by irradiating the surface of a metal material with pulsed laser light, but the present invention is not limited to this. For example, an electric field may be applied to the plasma to enhance the brightness of the plasma generated by the pulsed laser light. By enhancing the brightness of the plasma generated in the atmosphere, the instantaneous melting range reaches deeper, and thus the thickness of the nitride film can be increased. In order to apply an electric field to the plasma, the nitride film forming apparatus 1 may be configured as follows.

[0054] As shown in Figure 7, the nitride film forming apparatus 1 further comprises a pair of electrodes 19a arranged to straddle the irradiation path of laser light focused by a focusing optical system 12, and a voltage source 19b connected to each of the pair of electrodes 19a, which generates an electric field that increases the plasma generated between the pair of electrodes 19a. Each electrode 19a can be of any shape and material, but for example, it is a rod-shaped electrode made of tungsten. The distance between each electrode 19a is, for example, in the range of 0.5 cm to 2 cm, preferably about 1 cm. The voltage source 19b is a high-voltage source that generates a DC voltage (for example, about several kV). The electric field value generated in space by the voltage source 19b is preferably, for example, 500 kV / m or more.

[0055] The electric field generated between the pair of electrodes 19a must be applied at least when plasma is generated by laser irradiation, and as long as this condition is met, it may be a continuous electric field or a pulsed electric field. When a pulsed electric field is applied, the pulse width of the pulsed electric field is preferably in the range of, for example, 1 msec to 100 msec, considering the duration of the plasma. Alternatively, the pulsed electric field generated between the pair of electrodes 19a may be synchronized with the emission of pulsed laser light from the pulsed laser light source 11 by connecting the voltage source 19b to the control device 14 and having the control device 14 control the timing of the generation of the pulsed electric field. Specifically, for example, a pulsed electric field may be applied with the same frequency as the pulsed laser light and with a pulse width that includes the period from immediately before emission of the pulsed laser light to immediately after emission of the pulsed laser light.

[0056] In the above embodiment, a focusing optical system 12 separate from the pulsed laser light source 11 focused the pulsed laser light from the pulsed laser light source 11, but the present invention is not limited to this. For example, a focusing optical system (e.g., a convex lens) may be provided inside the pulsed laser light source 11 to focus the pulsed laser light emitted from the transmissive mirror of the oscillator. Alternatively, the laser energy may be spatially increased in density by focusing the beam emitted from the transmissive mirror of the oscillator of the pulsed laser light source 11 through an extraction window.

[0057] The embodiments described above are illustrative, and the present invention is not limited thereto. Various embodiments are possible without departing from the spirit of the invention as described in the claims. The components described in the embodiments and modifications can be freely combined. Furthermore, inventions equivalent to the invention described in the claims are also included in the present invention.

[0058] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0059] (Example 1) In Example 1, focused pulsed laser light was repeatedly irradiated onto each titanium material sample, and X-ray diffraction (XRD) analysis was performed on the film formed on the sample surface. XRD is a method for identifying compounds contained in the sample material by detecting the reflected X-rays that are reflected from the sample surface out of the X-rays irradiated onto the sample, and determining which angles of reflected X-rays are constructively interfering with each other. In Example 1, the number of pulsed laser light irradiations applied to each sample was varied, and the changes that occur on the sample surface by repeatedly irradiating the same area of ​​the sample with pulsed laser light were investigated. The pulse energy of the pulsed laser light was set to 25 mJ. Converted to a pulse energy density, this is 300 J / mm². 2 That is the case.

[0060] The experimental results are shown in Figure 8. In Figure 8, the vertical axis represents the intensity (count) of reflected X-rays, and the horizontal axis represents the angle 2θ. As shown in Figure 8, regardless of the number of irradiations, the presence of peaks at angle 2θ corresponding to TiN and Ti2N was confirmed for all samples. Furthermore, the TiN and Ti2N films were thickest when the number of irradiations was 5, and the thickness of the TiN and Ti2N films did not increase further even when the number of irradiations was increased. From the above, it can be understood that when the pulse energy density is relatively small, it is preferable to repeat the irradiation with pulsed laser light multiple times in order to obtain a TiN and Ti2N film of a certain thickness.

[0061] Next, the pulse energy of the pulsed laser light irradiated onto the sample is set to 400 mJ (which translates to a pulse energy density of 5000 J / mm²). 2 The samples were irradiated with pulsed laser light without changing any other conditions. As a result, as shown in Figure 9, it was confirmed that TiN and Ti2N coatings were formed on all samples regardless of the number of irradiations. Furthermore, it was confirmed that the TiN and Ti2N coatings were thickest when the number of irradiations was 1, and that the TiN and Ti2N coatings did not become any thicker even when the number of irradiations was increased further. This is because the pulse energy density was 5000 J / mm². 2In this case, it is thought that a portion of the nitride film formed by the first irradiation is blown away by subsequent irradiations. From the above, it can be understood that when the pulse energy density is relatively high, the thickest TiN and Ti2N films can be formed with a single laser pulse, and repeated laser irradiation is unnecessary.

[0062] (Example 2) In Example 2, we investigated how the sample coating changes when the number of pulsed laser beam irradiations was kept constant and the pulse energy density of the pulsed laser beam was varied. The number of irradiations was 20, and the pulse energies were set to 25 mJ, 100 mJ, 200 mJ, 300 mJ, and 400 mJ (5 patterns). Converted to pulse energy density, each pattern was 300 J / mm². 2 1250 J / mm 2 , 2500 J / mm 2 3750 J / mm 2 5000 J / mm 2 As a result, as shown in Figure 10, it was confirmed that TiN and Ti2N coatings were formed on all samples regardless of the pulse energy density.

[0063] (Example 3) In Example 3, we investigated the differences in the sample coating depending on whether or not the pulsed laser beam was focused. The pulse energy of the pulsed laser beam was 400 mJ, and the pulse energy density when focused was 5000 J / mm². 2 The pulse energy density when not focused is 0.005 J / mm². 2 The number of irradiations was set to one for each case. As a result, as shown in Figure 11, when pulsed laser light was focused, TiN and Ti2N films were formed on the sample surface, whereas when pulsed laser light was not focused, a TiO2 film was formed on the sample surface.

[0064] Subsequently, cross-sections of each sample were observed using a scanning electron microscope (SEM). As shown in the SEM image in Figure 12, when pulsed laser light was focused, TiN and Ti2N films with thicknesses of 2.2 μm, 5.3 μm, and 6.7 μm were formed. On the other hand, when the light was not focused, TiO2 films with thicknesses of approximately 0.51 μm and 0.59 μm were formed. From the above, it was confirmed that the formation of TiN and Ti2N films in air can only be achieved when pulsed laser light is focused.

[0065] (Example 4) In Example 4, we investigated the differences that occur on the sample surface depending on whether or not pulsed laser light is focused. The pulse energy density was 300 J / mm². 2 or 5000 J / mm 2 The pulse frequency was 10 Hz and the pulse width was 5 ± 1 ns. Other conditions were the same as in Example 1. After irradiation with pulsed laser light, the sample surface was photographed using an SEM and a laser microscope, respectively, and the condition of the sample surface was observed.

[0066] Figure 13(a) is an SEM image of the sample surface irradiated with unfocused pulsed laser light, and Figure 13(b) is an SEM image of the sample surface irradiated with focused pulsed laser light. In both cases, the pulse energy density was 5000 J / mm². 2 When the pulsed laser beam was not focused, numerous micrometer-scale holes were formed, but the overall surface was flat. On the other hand, when the pulsed laser beam was focused, a characteristic waveform structure and numerous microcracks were randomly formed. This waveform structure and microcracks are traces of melted titanium. Furthermore, when the pulsed laser beam was focused, the pulse energy density was 300 J / mm². 2 Even with pulsed laser light, a smooth waveform structure was formed, but no microcracks were generated. This difference is due to an energy density of 300 J / mm² per pulse. 2 This is thought to be because, with pulsed laser light, only the surface melts, and the melted region does not spread in the depth direction.

[0067] Figure 14(a) is a laser microscope image of the sample surface irradiated with unfocused pulsed laser light, and Figure 14(b) is a laser microscope image of the sample surface irradiated with focused pulsed laser light. When the pulsed laser light is not focused, the sample surface is almost flat, whereas when the pulsed laser light is focused, grooves and spot-like concave areas are formed. When irradiated with unfocused pulsed laser light, the sample surface remains solid, so it is thought that a normal thermal reaction occurs, generating an oxide layer and rapidly quenching, resulting in the formation of numerous voids on the sample surface. On the other hand, when irradiated with focused pulsed laser light, the sample surface melts instantaneously, and radicalized nitrogen preferentially penetrates the molten titanium, so it is thought that a TiN film or Ti2N film is formed depending on the amount of nitrogen in the reaction field. [Explanation of symbols]

[0068] 1. Nitride film forming apparatus 11. Pulsed laser light source 11a Signal generator 12 Focusing optical system 13 Moving Stages 14 Control device 15 Hanging devices 16 Robot Arms 17 Holder 18 Distance Sensor 19a electrode 19b Voltage source

Claims

1. A nitride film forming apparatus for forming a nitride film on a surface of a metal material, a pulsed laser light source that repeatedly emits a pulsed laser light having an energy density per pulse set so that the pulsed laser light irradiated onto the surface of the metal material generates plasma in the atmosphere around the surface of the metal material, thereby locally melting the surface of the metal material and generating activated nitrogen in the atmosphere; Nitride coating formation equipment.

2. the nitride film forming apparatus further includes a focusing optical system provided on an emission side of the pulsed laser light source and configured to focus the pulsed laser light emitted from the pulsed laser light source on the surface of the metal material, thereby generating plasma in the atmosphere around the surface of the metal material. The nitride film forming apparatus according to claim 1 .

3. the nitride film forming apparatus further includes a holding means provided on an exit side of the focusing optical system and holding a metal material such that a surface of the metal material is positioned at a focal position of the laser light focused by the focusing optical system. The nitride film forming apparatus according to claim 2 .

4. the holding means is a moving stage that moves the metal material relative to the focusing optical system, the nitride film forming apparatus further includes a control unit that controls an operation of the moving stage so that the pulsed laser light irradiated onto the surface of the metal material traces a predetermined trajectory. The nitride film forming apparatus according to claim 3.

5. The nitride film forming apparatus includes: a robot arm that movably supports the pulsed laser light source and the focusing optical system; and a control means for controlling the operation of the robot arm so that the pulsed laser light irradiated to the surface of the metal material traces a predetermined trajectory. The nitride film forming apparatus according to claim 2 or 3.

6. The energy density per pulse of the pulsed laser light irradiated onto the surface of the metal material is 1000 J / mm ２ ~6000 J / mm ２ is within the range of The nitride film forming apparatus according to any one of claims 1 to 5.

7. The nitride film forming apparatus includes: A pair of electrodes arranged to sandwich an irradiation path of the pulsed laser light emitted from the pulsed laser light source; and a voltage source connected to each of the pair of electrodes to generate an electric field between the pair of electrodes that increases the brightness of plasma generated by irradiating the surface of the metal material with the pulsed laser light emitted from the pulsed laser light source. The nitride film forming apparatus according to any one of claims 1 to 6.

8. The metal material is any one of a titanium material, a steel material, an aluminum material, a niobium material, and a zirconium material. The nitride film forming apparatus according to any one of claims 1 to 7.

9. A nitride film forming method for forming a nitride film on a surface of a metal material, comprising the steps of: a step of repeatedly emitting a pulsed laser beam having an energy density per pulse set so that the pulsed laser beam irradiated onto the surface of the metal material generates plasma in the atmosphere around the surface of the metal material, thereby locally melting the surface of the metal material and generating activated nitrogen in the atmosphere, A method for forming a nitride film.

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