Nitride film forming apparatus 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] Metallic materials with nitride films formed on their surfaces are known to have excellent abrasion resistance and corrosion resistance, making them suitable for use in machine parts. Nitride films are formed using gas nitriding, in which titanium materials are heated in an ammonia atmosphere, or plasma nitriding, which utilizes glow discharge. Because these methods form nitride films over the entire surface of metallic materials, there is a demand for techniques for selectively forming nitride films on parts of metallic material surfaces. For example, Patent Document 1 discloses a method for selectively forming nitride films on the laser-irradiated portions of a titanium material surface by irradiating a laser while spraying nitrogen gas onto the titanium material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-212395 Summary of the Invention [Problem to be solved by the invention]

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

[0005] The present invention has been made based on the above background, and aims to provide a nitride film forming apparatus and a nitride film forming method that are capable of selectively forming a nitride film on a metal surface using a simple technique. [Means for solving the problem]

[0006] In order to achieve the above object, a nitride film forming apparatus according to a first aspect of the present invention comprises: A nitride film forming apparatus for forming a nitride film on a surface of a metal material, The apparatus includes a pulsed laser light source that repeatedly emits pulsed laser light, the energy density of which is set per pulse, 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.

[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 focuses the pulsed laser light emitted from the pulsed laser light source onto the surface of the metal material, thereby generating plasma in the atmosphere around the surface of the metal material.

[0008] The nitride film forming device is provided on the output side of the focusing optical system, and is configured so that the surface of the metal material is positioned at the focal position of the laser light focused by the focusing optical system. Gold The apparatus may further comprise a holding means for holding the metal material.

[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 a control unit that controls the operation of the moving stage so that the pulsed laser light irradiated onto the surface of the metal material traces a predetermined trajectory.

[0010] The nitride film forming device includes: a robot arm that movably supports the pulsed laser light source and the focusing optical system; The apparatus may further comprise a control means for controlling the operation of the robot arm so that the pulsed laser light irradiated onto the surface of the metal material traces a predetermined trajectory.

[0011] The energy density per pulse of the pulsed laser light irradiated onto the surface of the metal material is 1000 J / mm 2 ~6000J / mm 2 may be in the range of

[0012] The nitride film forming device includes: a pair of electrodes arranged to sandwich an irradiation path of the pulsed laser light emitted from the pulsed laser light source; The laser may further include a voltage source connected to each of the pair of electrodes, and generating 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.

[0013] gold 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 comprises: A nitride film forming method for forming a nitride film on a surface of a metal material, comprising: The method includes a step of repeatedly emitting pulsed laser light, the energy density of which is set per pulse, 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. [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 it with a pulsed laser beam, even in the atmosphere. Therefore, a nitride film forming apparatus and a nitride film forming method can be provided that can selectively form a nitride film on a metal surface using a simple technique. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing a configuration of a nitride film forming apparatus according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating the mechanism of nitriding treatment of a titanium material in air according to an embodiment of the present invention. FIG. [Figure 3] FIG. 2 is a plan view showing an example of a trajectory of a pulsed laser beam according to an embodiment of the present invention. [Figure 4] FIG. 10 is a plan view showing another example of a trajectory of a pulsed laser beam according to an embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing the configuration of a nitride film forming apparatus according to a first modified example of the present invention. [Figure 6] FIG. 10 is a diagram showing the configuration of a nitride film forming apparatus according to a second modified example of the present invention. [Figure 7] FIG. 10 is a diagram showing the configuration of a nitride film forming apparatus according to a third modified example of the present invention. [Figure 8] 1 is a graph showing an X-ray diffraction pattern of a titanium material irradiated with pulsed laser light having an energy density per pulse of 300 J / mm 2 in Example 1. [Figure 9] 1 is a graph showing an X-ray diffraction pattern of a titanium material irradiated with pulsed laser light having an energy density per pulse of 5000 J / mm 2 in Example 1. [Figure 10] 10 is a graph showing an X-ray diffraction pattern of a titanium material irradiated with pulsed laser light 20 times in Example 2. [Figure 11] 10 is a graph showing the difference in X-ray diffraction pattern of a titanium material depending on whether or not the pulsed laser light is focused in Example 3. [Figure 12] FIG. 10 is a view showing a scanning electron microscope image of the titanium material in Example 3. [Figure 13] 1(a) and 1(b) are both scanning electron microscope images of the titanium material in Example 4. [Figure 14]10(a) and 10(b) are both laser microscope images of the titanium material in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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 below with reference to the drawings. In the embodiment, a nitride film is formed on the surface of a plate-shaped titanium material as a metal material.

[0018] FIG. 1 is a diagram showing 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 of its components, but a surface layer whose main component is at least a nitride compound. Hereinafter, an orthogonal coordinate system will be used in which the left-right direction in FIG. 1 is the X-axis direction, the direction perpendicular to FIG. 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). Hereinafter, the surface of the titanium material will be assumed to be located on the XY plane.

[0019] The nitride film forming apparatus 1 includes a pulsed laser source 11 that emits pulsed laser light, a focusing optical system 12 that focuses the laser light from the pulsed laser 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 its surface is positioned at a position (focal position) 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 control device 14 are connected to each other so that they can 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 (pulse laser light) at a constant frequency and pulse width. The pulsed laser light source 11 includes, for example, an Nd:YAG (Yttrium Aluminum Garnet) laser. In addition, for example, a Q switch (shutter) is provided inside the oscillator of the pulsed laser light source 11.

[0021] A signal generator 11a that generates a signal for oscillating the pulsed laser light source 11 is connected to the pulsed laser light source 11, and the pulsed laser light source 11 emits pulsed laser light by turning on and off the current from the signal generator 11a. The signal generator 11a sets various parameters of the pulsed laser light emitted from the pulsed laser light source 11 based on instructions from a user. Note that, to obtain a pulse waveform from the pulsed laser light source 11, the laser light continuously oscillated from the laser light source may be configured to be turned on and off by a modulator or a 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 includes, 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 hanging fixture 15 and are disposed above a moving stage 13. The focusing optical system 12 focuses the pulsed laser light, thereby increasing the energy per unit area (energy density) at the focal position of the pulsed laser light.

[0023] Figure 2 is a schematic diagram illustrating the mechanism of nitriding of titanium material in the atmosphere. Titanium material preferentially bonds with oxygen, so even if a continuous wave laser is irradiated onto the surface of the 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 the titanium material, nitrogen molecules in the atmosphere near the titanium surface are taken into the titanium material and bond with titanium atoms, forming a nitride film on the surface of the titanium material.

[0024] Specifically, when a pulsed laser beam with increased energy density due to focusing is irradiated onto the surface of a titanium material, the laser energy is concentrated in time and space, generating a localized plasma consisting of nitrogen, oxygen, and metal material components in the air surrounding the irradiated area. Energy transfer from this plasma instantaneously melts the surface of the metal material, including the original oxide film, generating convection in the molten titanium. This convection preferentially incorporates activated nitrogen components from the air into the molten titanium, forming a nitride film on the surface of the metal material. Note that nitride film formation can also be achieved on other metal materials using a similar mechanism.

[0025] To melt the surface of a titanium material using plasma in the atmosphere, the frequency of the pulsed laser beam is preferably, for example, 10 Hz or less, and the pulse width is preferably about several nanoseconds, for example, in the range of 1 to 5 nanoseconds. Furthermore, when the pulse width is about several nanoseconds, the pulse energy density (the energy per pulse of the pulsed laser beam) may be set to a level such that the pulsed laser beam irradiated onto the surface of the titanium material generates plasma in the atmosphere around the surface of the titanium material, thereby locally melting the surface of the titanium material and generating activated nitrogen in the atmosphere.

[0026] Pulse energy density is at least 1000J / mm 2 It is preferable that the 2 ~6000J / mm 2 It is more preferable that the range is 1000 J / mm 2 ~5000J / mm 2 It is even more preferable that the pulse energy density of the pulsed laser beam be within the range of 1000 . The optimum value for the pulse energy density of the pulsed laser beam may be determined in advance by experiment, taking into consideration the film thickness of the nitride coating on the titanium material. The frequency and pulse width of the pulsed laser beam may be set based on the pulse energy density of the pulsed laser beam, the beam cross-sectional area, and the moving speed of the moving stage.

[0027] Returning to Figure 1, moving stage 13 is an example of a holding means for holding the titanium material so that the surface of the titanium material is positioned at the position where the pulsed laser light is focused by focusing optical system 12. While holding the titanium material to be processed, moving stage 13 moves the titanium material in the X-axis and Y-axis directions so that the pulsed laser light from 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. The first motor and the second motor are both connected to a motor driver, and the motor driver is connected to the control device 14.

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

[0030] 3 is a plan view showing an example of the trajectory of the pulsed laser beam according to the embodiment. In the trajectory of the pulsed laser beam in FIG. 3, the focus of the pulsed laser beam is moved in the +X direction from one end to the other end of a rectangular processing area where a nitride coating is to be 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 one 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] 4 is a plan view showing another example of the trajectory of the pulsed laser beam according to the embodiment. The trajectory of the pulsed laser beam in FIG. 4 is a trajectory that sequentially traces a plurality of circles having the same center point but different diameters in a circular processing region. When the pulsed laser beam is moved in the radial direction, it is preferable to stop the irradiation of the pulsed laser beam until the radial movement is completed. Note that in the circular processing region, the pulsed laser beam may be set to trace a spiral trajectory.

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

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

[0034] 1, the control device 14 is, for example, a general-purpose computer including a memory and a processor. The control device 14 is an example of a control means that controls the operations of the pulse laser light source 11 and the moving stage 13 by causing the processor to execute a program stored in the memory.

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

[0036] Next, the flow of the nitride film forming method for titanium material, which is carried out using the nitride film forming apparatus 1 according to the embodiment, will be described.

[0037] First, the titanium material on which the nitride film is to be formed is held on the moving stage 13 .

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

[0039] Next, when the user operates the operation unit of control device 14 to instruct the start of laser irradiation, control device 14 causes pulsed laser light to be emitted from pulsed laser light source 11 based on the processing conditions stored in memory, and also moves moving stage 13 from the start point of the movement path. At this time, nitride film forming device 1 repeats a step (emitting step) in which pulsed laser light is emitted from pulsed laser light source 11 at each spot on the movement path, and a step (focusing step) in which the pulsed laser light emitted in the emitting step is focused on one spot on the surface of the titanium material, thereby forming nitride films sequentially along the path on the surface of the titanium material.

[0040] Next, when the moving object reaches the end point of the moving path stored in the memory, the control device 14 causes the pulse laser source 11 to terminate irradiation of the pulse laser light. The above is the flow of the method for forming a nitride film on titanium material.

[0041] As described above, the nitride coating formation apparatus 1 according to the embodiment includes a pulsed laser source 11 that emits pulsed laser light and a focusing optical system 12 that is provided on the output side of the pulsed laser source 11 and focuses the pulsed laser light emitted from the pulsed laser source 11 onto the surface of a titanium material. The energy density per pulse of the pulsed laser source 11 is set so that the pulsed laser light generates nitrogen plasma in the atmosphere, locally melting the surface of the titanium material and generating activated nitrogen in the atmosphere. Therefore, a nitride coating can be formed on the surface of a titanium material even in the atmosphere by concentrating the laser energy temporally and spatially. Furthermore, because the nitride coating can be formed in the atmosphere, there is no need to limit the size of the target on which the nitride coating is to be formed. Furthermore, because the nitride coating is formed only in the area irradiated with the pulsed laser light, the nitride coating can be selectively formed on a portion of the titanium material surface.

[0042] In addition, the nitride film forming apparatus 1 according to the embodiment has an energy density per pulse emitted from the pulse laser light source 11 of preferably 1000 J / mm 2 ~6000J / mm 2This is within the range. Therefore, it is possible to prevent large deformation of the titanium material surface and a decrease in mechanical strength. Furthermore, when the 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 per pulse of approximately 100 mJ to 500 mJ, and since such pulsed laser light sources 11 are available at low cost, the manufacturing cost of the nitride coating formation apparatus 1 can be reduced.

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

[0044] (Variation) In the above embodiment, the nitride coating forming apparatus 1 is provided with one pulsed laser light source 11 and one focusing optical system 12, but the present invention is not limited to this. For example, a nitride coating may be rapidly formed on the surface of a titanium material by providing a plurality of pairs of pulsed laser light source 11 and focusing optical system 12.

[0045] In the above embodiment, the surface of the titanium material is moved relative to the focused pulsed laser light by moving the moving stage 13 with respect to the focusing optical system 12, but the present invention is not limited to this. For example, as shown in Fig. 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 and Y-axis directions. In this case, the titanium material may be held by a holder 17 that does not have a movement mechanism.

[0046] According to the above modification, the nitride film forming apparatus 1 can be placed at any position in the production line, and nitride films can be formed on parts or products in the middle of the production line. Note that the nitride film forming apparatus 1 may also be used to form nitride films on parts or products as an afterthought, or to form nitride films for repairing or reinforcing parts or products.

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

[0048] 6, a distance sensor 18 may be further provided to measure the distance between the focusing optical system 12 and the titanium material, and the operation of the robot arm 16 may be controlled based on a signal from the distance sensor 18 so as to maintain a constant distance between the surface of the titanium material held by the holder 17 and the focusing optical system 12. As a specific example of the above process, PID (Proportional-Integral-Differential) control may be performed.

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

[0050] In the above embodiment, the control device 14 is connected to the signal generator 11a of the pulsed laser light source 11, and the signal generator 11a turns the current on and off based on a signal from the control device 14, but the present invention is not limited to this. For example, the present invention may be configured so that a user directly operates the signal generator 11a 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 coating is formed on the surface of a plate-shaped titanium material, but the present invention is not limited to this. The shape of the titanium material is arbitrary, and it may be, for example, box-shaped, spherical, or concave.

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

[0053] In the above embodiment, plasma is generated in the atmosphere simply by irradiating the surface of the 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 increase the brightness of the plasma generated by the pulsed laser light. Increasing the brightness of the plasma generated in the atmosphere allows the instantaneous melting range to reach a deeper area, thereby increasing the thickness of the nitride film. 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 FIG. 7, the nitride film forming apparatus 1 further includes a pair of electrodes 19a arranged on either side of the irradiation path of the laser light focused by the focusing optical system 12, and voltage sources 19b connected to the pair of electrodes 19a, respectively, for generating an electric field that enhances the plasma generated between the pair of electrodes 19a. Each electrode 19a may be of any shape and material, but may be, for example, a rod-shaped electrode made of tungsten. The spacing between the electrodes 19a is, for example, within a range of 0.5 cm to 2 cm, preferably about 1 cm. The voltage source 19b is a high-voltage voltage source that generates a DC voltage (e.g., about several kV). The value of the electric field generated in the space by the voltage source 19b is, for example, 500 kV / m or more.

[0055] The electric field generated between the pair of electrodes 19a needs to be applied at least during plasma generation due to 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 within a range of, for example, 1 msec to 100 msec, taking into account the duration of plasma. Furthermore, the voltage source 19b may be connected to the control device 14, and the control device 14 may control the timing of generating the pulsed electric field, thereby synchronizing the pulsed electric field generated between the pair of electrodes 19a with the emission of the pulsed laser light from the pulsed laser light source 11. Specifically, for example, a pulsed electric field may be applied at the same frequency as the frequency of the pulsed laser light and with a pulse width that includes the period from immediately before the emission of the pulsed laser light to immediately after the emission of the pulsed laser light.

[0056] In the above embodiment, the focusing optical system 12 separate from the pulsed laser light source 11 focuses 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 transmission mirror of the oscillator. Furthermore, the laser energy may be spatially denser by narrowing and extracting the beam emitted from the transmission mirror of the oscillator of the pulsed laser light source 11 using an extraction window.

[0057] The above-described embodiments are merely examples, and the present invention is not limited to these. Various embodiments are possible within the scope of the invention as set forth in the claims. The components described in the embodiments and modifications can be freely combined. Furthermore, inventions equivalent to the inventions set forth in the claims are also included in the present invention.

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

[0059] Example 1 In Example 1, each titanium material sample was repeatedly irradiated with focused pulsed laser light, and X-ray diffraction analysis (XRD) was performed on the coating formed on the sample surface. XRD is a technique for identifying compounds contained in the sample material by detecting the X-rays reflected from the sample surface among the X-rays irradiated to the sample, and determining at what angle the reflected X-rays constructively interact with each other. In Example 1, the number of times that each sample was irradiated with pulsed laser light was changed, and the changes that occurred on the sample surface when the same location on the sample was repeatedly irradiated with pulsed laser light were examined. The pulse energy of the pulsed laser light was 25 mJ, which is equivalent to a pulse energy density of 300 J / mm 2 is.

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

[0061] Next, the pulse energy of the pulsed laser light irradiating the sample was set to 400 mJ (equivalent to a pulse energy density of 5000 J / mm 2 ) and irradiated the samples with pulsed laser light without changing any other conditions. As a result, as shown in Figure 9, it was confirmed that TiN and Ti2N films were formed on all samples regardless of the number of irradiations. It was also confirmed that the TiN and Ti2N films were thickest when the number of irradiations was one, and that the TiN and Ti2N films did not become thicker even if the number of irradiations was increased beyond that. This was because the pulse energy density was 5000 J / mm 2In this case, it is thought that part of the nitride coating formed by one irradiation is blown away by the second or subsequent irradiation. From the above, it can be seen that when the pulse energy density is relatively high, the thickest TiN and Ti2N coatings can be formed by one laser pulse irradiation, and repeated laser irradiation is not necessary.

[0062] Example 2 In Example 2, the number of irradiations of the pulsed laser light was kept constant, and the pulse energy density of the pulsed laser light was varied to examine what changes would occur in the coating of the sample. The number of irradiations was set to 20, and the pulse energy was set to five patterns: 25 mJ, 100 mJ, 200 mJ, 300 mJ, and 400 mJ. When converted to a pulse energy density, each pattern was 300 J / mm 2 , 1250J / mm 2 , 2500J / mm 2 , 3750J / mm 2 , 5000J / mm 2 As a result, as shown in Figure 10, it was confirmed that TiN and Ti2N films were formed on all samples regardless of the pulse energy density.

[0063] Example 3 In Example 3, it was verified what kind of difference occurs in the coating of the sample depending on whether or not the pulse laser light is focused. The pulse energy of the pulse laser light is 400 mJ, and the pulse energy density when focused is 5000 J / mm 2 , the pulse energy density without focusing is 0.005J / mm 2 The number of irradiation times for each was one. As a result, as shown in Figure 11, when the pulsed laser beam was focused, TiN and Ti2N films were formed on the surface of the sample, whereas when the pulsed laser beam was not focused, a TiO2 film was formed on the surface of the sample.

[0064] The cross section of each sample was then observed using a scanning electron microscope (SEM). As shown in the SEM images in Figure 12, when the pulsed laser beam 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 pulsed laser beam 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 TiN and Ti2N films can be formed in air only when the pulsed laser beam is focused.

[0065] Example 4 In Example 4, we investigated the difference in the sample surface depending on whether or not the pulsed laser beam was focused. The pulse energy density was 300 J / mm 2 or 5000J / mm 2 The pulse frequency was 10 Hz and the pulse width was 5±1 ns. The other conditions were the same as in Example 1. After irradiation with the pulsed laser light, the sample surface was photographed using an SEM and a laser microscope, respectively, to observe the state of the sample surface.

[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 / mm 2 When the pulsed laser beam was not focused, numerous micrometer-scale holes were formed, but the surface was generally flat. On the other hand, when the pulsed laser beam was focused, a characteristic wave-like structure and numerous fine cracks were randomly formed. These wave-like structures and fine cracks are traces of titanium melting. Furthermore, when the pulsed laser beam was focused, the surface was flat even when the pulse energy density was 300 J / mm 2 A smooth wave structure was formed even with pulsed laser light of 300 J / mm, but no microcracks were generated. This difference is due to the energy density per pulse of 300 J / mm. 2 This is thought to be because the pulsed laser beam melts only the surface portion and the melted region does not spread in the depth direction.

[0067] Figure 14(a) shows a laser microscope image of the sample surface irradiated with an unfocused pulsed laser beam, and Figure 14(b) shows a laser microscope image of the sample surface irradiated with a focused pulsed laser beam. When the pulsed laser beam was unfocused, the sample surface was nearly flat, whereas when the pulsed laser beam was focused, grooves and spot-like depressions were formed. When the unfocused pulsed laser beam was irradiated, the sample surface remained solid, and a normal thermal reaction occurred, producing an oxide layer. This rapid quenching likely resulted in the formation of numerous voids on the sample surface. When the focused pulsed laser beam was irradiated, the sample surface instantly melted, and nitrogen radicals preferentially penetrated the molten titanium, resulting in the formation of a TiN or TiN coating depending on the amount of nitrogen present in the reaction field. [Explanation of symbols]

[0068] 1. Nitriding film forming equipment 11 Pulsed laser light source 11a Signal Generator 12 Focusing optical system 13 Moving Stage 14 Control device 15 Hanging equipment 16 Robotic Arm 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 pulsed laser light, the energy density per pulse of which is 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; Nitriding film forming equipment.

2. the nitride film forming apparatus further includes a focusing optical system provided on an emission side of the pulsed laser light source, for focusing the pulsed laser light emitted from the pulsed laser light source onto 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 the metal material so that the 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 the 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 device includes: a robot arm that movably supports the pulsed laser light source and the focusing optical system; a control means for controlling the operation of the robot arm 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 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 device includes: a pair of electrodes arranged to sandwich an irradiation path of the pulsed laser light emitted from the pulsed laser light source; a voltage source connected to each of the pair of electrodes, and generating 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: a step of repeatedly emitting 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, Nitriding film formation method.

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