JP2022108281A - Nitride film forming device and nitride film forming method - Google Patents

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

The present invention relates to a nitride film forming apparatus and a nitride film forming method.

A metal material having a nitride film formed on its surface is known to be excellent in wear resistance and corrosion resistance and suitable for mechanical parts. A gas nitriding method in which a titanium material is heated in an ammonia atmosphere and a plasma nitriding method using glow discharge are used to form the nitride film. Since these methods form a nitride film on the entire surface of the metal material, there is a demand for a method of selectively forming a nitride film on a part of the surface of the metal material. For example, Patent Literature 1 discloses a method of selectively forming a nitride film on a laser-irradiated portion of the surface of a titanium material by irradiating the titanium material with a laser while nitrogen gas is being sprayed thereon.

JP-A-6-212395

In the method of Patent Document 1, since nitrogen gas is sprayed during the formation of the nitride film, it is necessary to prepare gas spraying equipment and a large amount of nitrogen gas in advance, and it is not suitable for mass production of metal parts on which the nitride film is formed. . For this reason, there is a demand for a method capable of selectively forming a nitride film on a metal surface without blowing nitrogen gas. Such problems exist 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.

SUMMARY OF THE INVENTION It is an object of the present invention to provide 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 technique. .

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

The nitride film forming apparatus is provided on the emission side of the pulse laser light source, and converges the pulse laser light emitted from the pulse laser light source on the surface of the metal material to form a Focusing optics may also be provided to generate the plasma.

The nitride film forming device is provided on the output side of the focusing optical system and holds the metal material so that the surface of the metal material is positioned at the focal position of the laser beam focused by the focusing optical system. may be further provided.

the holding means is a moving stage that moves the metal material with respect to the focusing optical system;
The nitride film forming apparatus may further include control means for controlling the operation of the moving stage so that the pulsed laser beam irradiated onto the surface of the metal material traces a predetermined trajectory.

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

The energy density per pulse of the pulsed laser light with which the metal material surface is irradiated may be within the range of 1000 J/mm ² to 6000 J/mm ² .

The nitride film forming device is
a pair of electrodes arranged to sandwich an irradiation path of the pulsed laser light emitted from the pulsed laser light source;
An electric field is generated between the pair of electrodes, which is connected to the pair of electrodes, respectively, and increases the luminance of plasma generated by irradiating the surface of the metal material with the pulsed laser light emitted from the pulsed laser light source. and a voltage source.

The metal material may be any one of titanium material, steel material, aluminum material, niobium material and zirconium material.

In order to achieve the above object, a method for forming a nitride film according to a second aspect of the present invention comprises:
A nitride film forming method for forming a nitride film on the surface of a metal material,
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 step of repeatedly emitting pulsed laser light having a set energy density per pulse is included.

According to the present invention, a nitride film can be formed on the surface of a metal material simply by irradiating a pulsed laser beam even in the atmosphere. Therefore, it is possible to provide 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 technique.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the nitride film formation apparatus which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining the mechanism of the nitriding process of the titanium material in the air|atmosphere based on embodiment of this invention. FIG. 2 is a plan view showing an example of the trajectory of pulsed laser light according to the embodiment of the present invention; FIG. 5 is a plan view showing another example of the trajectory of pulsed laser light according to the embodiment of the present invention; It is a figure which shows the structure of the nitride film formation apparatus based on the 1st modification of this invention. It is a figure which shows the structure of the nitride film formation apparatus based on the 2nd modification of this invention. It is a figure which shows the structure of the nitride film formation apparatus based on the 3rd modification of this invention. 2 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. FIG. 2 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. FIG. 4 is a graph showing an X-ray diffraction pattern of a titanium material irradiated with pulsed laser light 20 times in Example 2. FIG. 10 is a graph showing the difference in X-ray diffraction pattern of titanium material depending on whether or not the pulsed laser beam is condensed in Example 3. FIG. FIG. 10 is a diagram showing a scanning electron microscope image of the titanium material in Example 3; (a) and (b) are both scanning electron microscope images of the titanium material in Example 4. FIG. (a) and (b) are both laser microscope images of the titanium material in Example 4. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION An apparatus for forming a nitride film on a metal material and a method for forming a nitride film on a metal material according to embodiments of the present invention will be described below in detail with reference to the drawings. In the embodiments, an example will be described in which a nitride film is formed on the surface of a plate-like titanium material as the metal material.

FIG. 1 is a diagram showing the configuration of a nitride film forming apparatus according to an embodiment. A nitride film forming apparatus 1 is an apparatus for forming a nitride film on the surface of a titanium material. A nitride film is not a surface layer containing nitrogen as one component, but a surface layer containing at least a nitride compound as a main component. 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 (vertical direction). system. Hereinafter, it is assumed that the surface of the titanium material is arranged on the XY plane.

The nitride film forming apparatus 1 includes a pulse laser light source 11 that emits pulse laser light, a focusing optical system 12 that focuses the laser light from the pulse laser light source 11, and the laser light focused by the focusing optical system 12. A moving stage 13 for moving the titanium material with respect to a focusing optical system 12 while holding the titanium material so that the surface of the titanium material is placed at a position (focus position), and a laser beam focused on the surface of the titanium material. and a control device 14 for controlling the operation of the moving stage 13 so as to draw a trajectory of . The moving stage 13 and the controller 14 are communicably connected to each other via a wired or wireless communication circuit.

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 pulse laser light source 11 includes, for example, an Nd:YAG (Yttrium Aluminum Garnet) laser. A Q switch (shutter), for example, is provided in the oscillator of the pulse laser light source 11 .

A signal generator 11a for generating a signal for oscillating the pulse laser light source 11 is connected to the pulse laser light source 11, and the pulse laser light source 11 generates pulsed laser light by turning on and off the current from the signal generator 11a. emit. In the signal generator 11a, various parameters of the pulsed laser light emitted from the pulsed laser light source 11 are set based on instructions from the user. In order to obtain a pulse waveform from the pulse laser light source 11, the laser light continuously oscillated from the laser light source may be turned on and off by a modulator or a shutter.

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. Focusing optics 12 comprises, for example, one or more focusing lenses. A condensing lens is a convex lens, for example. The pulsed laser light source 11 and the focusing optical system 12 are connected to a suspension fixture 15 and arranged above the moving stage 13 . The focusing optical system 12 concentrates the pulsed laser beam, thereby increasing the energy per unit area (energy density) at the focal position of the pulsed laser beam.

FIG. 2 is a schematic diagram for explaining the mechanism of nitriding treatment of titanium material in the air. Titanium materials tend to preferentially bond with oxygen, so even if the titanium material surface is irradiated with a continuous wave laser in the atmosphere, a chemically stable oxide film is formed. On the other hand, when the pulsed laser beam is condensed by the focusing optical system 12 and irradiated onto the titanium material surface, nitrogen molecules in the atmosphere near the titanium surface are taken into the titanium material and combined with titanium atoms. A nitride film is formed on the surface of the titanium material.

More specifically, when a titanium material surface is irradiated with a pulsed laser beam whose energy density has been increased by focusing, and the laser energy is temporally and spatially concentrated, nitrogen, oxygen, and metal material components are released into the air around the irradiated area. A plasma consisting of is generated locally. The application of energy from this plasma instantaneously melts the surface of the metal material, including the original oxide film, and generates convection of the molten titanium. Due to this convection, the activated nitrogen component in the air is preferentially taken into the molten titanium, so that a nitride film is formed on the surface of the metal material. It should be noted that formation of a nitride film can also be realized by a similar mechanism with other metal materials.

In order to melt the titanium material surface by plasma in the atmosphere, the frequency of the pulsed laser light is preferably, for example, 10 Hz or less, and the pulse width is about several nanoseconds, for example, 1 to 5 nanoseconds. Preferably in the range of seconds. In addition, when the pulse width is about several nanoseconds, the pulse energy density, which is the energy per pulse of the pulsed laser light, is as follows: It may be set to such an extent that the generation locally melts the surface of the titanium material and generates activated nitrogen in the air.

The pulse energy density is preferably at least 1000 J/mm ² , more preferably in the range of 1000 J/mm ² to 6000 J/mm ² , such as in the range of 1000 J/mm ² to 5000 J/mm ² . It is even more preferable to have As for the pulse energy density of the pulsed laser light, an optimum value may be determined in advance by experiment, taking into account the film thickness of the nitride film of the titanium material. Also, the frequency and pulse width of the pulsed laser light may 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.

Returning to FIG. 1, the moving stage 13 is an example of holding means for holding the titanium material so that the surface of the titanium material is arranged at the position where the pulsed laser beam 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 beam from the focusing optical system 12 draws a set trajectory on the surface of the titanium material. move.

The moving stage 13 includes a base, a first moving member that moves with respect to the base in the X-axis direction, a first motor that moves the first moving member with respect to the substrate, and a first moving member. and a second motor for moving 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 the controller 14 .

The moving path of the moving stage 13 is set in consideration of the shape and size of the processing area for forming the nitride film on the surface of the titanium material and the cross-sectional shape and size of the focused pulsed laser beam. The moving path of the moving stage 13 is set, for example, so that the pulsed laser beam irradiated to the titanium material completely fills the processing area for forming the nitride film on the surface of the titanium material. A specific example of the trajectory of the pulsed laser light will be described below, where the cross-sectional shape of the pulsed laser light is circular.

FIG. 3 is a plan view showing an example of the trajectory of pulsed laser light according to the embodiment. In the trajectory of the pulsed laser beam in FIG. 3, the focal point of the pulsed laser beam is moved in the +X direction from one end to the other end of the rectangular processing area for forming the nitride film. Next, it is moved in the -Y direction by a distance corresponding 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 corresponding to the diameter of the pulsed laser beam. The above steps are repeated until the trajectory fills the machining area. When moving the trajectory of the pulsed laser light in the Y direction, it is preferable to stop the irradiation of the pulsed laser light until the movement in the Y direction is completed.

FIG. 4 is a plan view showing another example of the trajectory of pulsed laser light according to the embodiment. The trajectory of the pulsed laser beam in FIG. 4 is a trajectory that sequentially draws a plurality of circles having the same center point and different diameters in a circular processing area. When moving the pulsed laser light in the radial direction, it is preferable to stop the irradiation of the pulsed laser light until the movement in the radial direction is completed. In addition, in the circular processing area, the pulsed laser beam may be set so as to draw a spiral trajectory.

The moving speed of the moving stage 13 is set in consideration of various characteristics of the pulsed laser light such as pulse energy density, frequency and pulse width, and is, for example, within the range of 0.1 mm/s to 2 mm/s. In addition, the movement of the moving stage 13 may be performed by scanning continuously, or by intermittently repeating moving and stopping. For example, a plurality of spots that are adjacent to each other are set in the processing area, one spot is irradiated with the pulsed laser beam while the moving stage 13 is stopped, and then the adjacent spots are moved so that the pulsed laser beam can be irradiated. The stage 13 may be moved. Also, if the frequency is relatively high, the time interval between irradiations of the pulsed laser light becomes long. Therefore, even if the moving stage 13 is continuously scanned, the movement of the moving stage 13 is completed before the next irradiation timing. can be made

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

Returning to FIG. 1, controller 14 is, for example, a general purpose computer with memory and processor. The control device 14 is an example of control means for controlling the operations of the pulse laser light source 11 and the moving stage 13 by executing a program stored in a memory with a processor.

The control device 14 receives user instructions regarding the pulse energy density, frequency, pulse width and number of times of irradiation of the pulsed laser light, and the moving path and moving speed of the moving stage 13 . Upon receiving the user's instruction, the control device 14 controls the operation of the pulse laser light source 11 so that the pulse laser light source 11 oscillates at the set pulse energy density, frequency and pulse width of the pulse laser light. In addition, the control device 14 controls 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 irradiation times of the pulsed laser light, and the moving path and moving speed of the moving stage 13 . control behavior.
The above is the configuration of the nitride film forming apparatus 1 .

Next, the flow of the method for forming a nitride film on a titanium material, which is performed using the nitride film forming apparatus 1 according to the embodiment, will be described.

First, the moving stage 13 is caused to hold a titanium material on which a nitride film is to be formed.

Next, the user operates the operation unit of the control device 14 to control the pulse energy density, frequency, pulse width, number of times of irradiation of the pulsed laser beam, and the moving path and moving speed of the moving stage 13 (hereinafter referred to as collectively referred to as “processing conditions”). When the control device 14 receives a user's instruction regarding the processing conditions, the control device 14 stores information regarding the processing conditions in the memory.

Next, when the user operates the operation unit of the control device 14 to instruct the start of laser irradiation, the control device 14 causes the pulse laser light source 11 to emit pulse laser light based on the processing conditions stored in the memory. At the same time, the moving stage 13 is moved from the starting point of the moving path. At this time, the nitride film forming apparatus 1 emits a pulsed laser beam from the pulsed laser light source 11 at each spot on the movement path (an emission step), and the pulsed laser beam emitted in the emission step is applied to the surface of the titanium material. By repeating the step of condensing light onto one spot (condensing step), a nitride film is sequentially formed on the path of the surface of the titanium material.

Next, when the control device 14 reaches the end point of the movement path stored in the memory, the pulse laser light source 11 terminates irradiation of the pulse laser light.
The above is the flow of the method for forming a nitride film on a titanium material.

As described above, the nitride film forming apparatus 1 according to the embodiment includes the pulse laser light source 11 that emits the pulse laser light, and the pulse laser light source 11 that is provided on the emission side of the pulse laser light source 11 and emits a pulse emitted from the pulse laser light source 11. focusing optics 12 for focusing the laser light onto the titanium material surface. Further, in the pulsed laser light source 11, the energy density per pulse is such that the pulsed laser light generates nitrogen plasma in the air, thereby locally melting the surface of the titanium material and generating activated nitrogen in the air. is set. Therefore, even in the atmosphere, a nitride film can be formed on the titanium material surface by concentrating the laser energy temporally and spatially. Moreover, since the nitride film can be formed in the atmosphere, there is no need to limit the size of the object on which the nitride film is formed. Furthermore, since the nitride film is formed only on the region irradiated with the pulsed laser beam, the nitride film can be selectively formed on a part of the surface of the titanium material.

Further, in the nitride film forming apparatus 1 according to the embodiment, the energy density per pulse emitted from the pulse laser light source 11 is preferably within the range of 1000 J/mm ² to 6000 J/mm ² . Therefore, it is possible to suppress large deformation of the surface of the titanium material and decrease in mechanical strength. Further, when the pulsed laser light is focused by the focusing optical system 12, the above energy density can be realized by the pulsed laser light source 11 whose energy per pulse is about 100 mJ to 500 mJ, and such a pulsed laser light source 11 is available at low cost. Therefore, the manufacturing cost of the nitride film forming apparatus 1 can be suppressed.

The present invention is not limited to the above embodiments, and modifications described below are possible.

(Modification)
Although one pulse laser light source 11 and one focusing optical system 12 are provided in the nitride film forming apparatus 1 in the above embodiment, the present invention is not limited to this. For example, by providing a plurality of sets of the pulse laser light source 11 and the focusing optical system 12, a nitride film may be quickly formed on the surface of the titanium material.

In the above embodiment, the moving stage 13 is moved with respect to the focusing optical system 12 to move the surface of the titanium material relative to the focused pulsed laser beam. Not limited. For example, as shown in FIG. 5, the pulse laser light source 11 and the focusing optical system 12 are supported by the tip of the robot arm 16, and the tip of the robot arm 16 is moved in the X-axis direction and the Y-axis direction. may In this case, the titanium material may be held by a holder 17 that does not have a moving mechanism.

According to the above modification, the nitride film forming apparatus 1 can be arranged at any position on the production line, and the formation of the nitride film on the parts and products can be realized in the middle of the production line. Incidentally, the nitride film forming apparatus 1 may be used to form a nitride film on a component or product as a post-installation, or to form a nitride film for repairing or reinforcing a component or product.

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

Specifically, as shown in FIG. 6, a distance sensor 18 for measuring the distance between the focusing optical system 12 and the titanium material is further provided, and based on the signal from the distance sensor 18, the titanium material held by the holder 17 is detected. The movement of the robot arm 16 may be controlled to keep the distance between the surface and the focusing optics 12 constant. PID (Proportional-Integral-Differential) control may be executed as the specific processing described above.

In addition, the moving stage 13 is also configured to be movable in the Z-axis direction, and the distance between the titanium material surface held by the moving stage 13 and the focusing optical system 12 is kept constant based on the signal from the distance sensor 18. The motion of the moving stage 13 in the Z-axis direction may be controlled so that

In the above embodiment, the control device 14 is connected to the signal generator 11a of the pulse laser light source 11, and the signal generator 11a turns on and off the current based on the signal from the control device 14. is not limited to For example, the user may directly operate the signal generator 11a to set parameters such as the pulse energy density, frequency, and pulse width of the pulsed laser beam.

Although the nitride film is formed on the surface of the plate-like titanium material in the above embodiment, the present invention is not limited to this. The shape of the titanium material is arbitrary, and may be, for example, box-like, spherical, or concave.

In the above embodiment, the nitride film is formed on the titanium material in the air, but the present invention is not limited to this. For example, a nitride film may be formed on other metal materials such as steel materials, aluminum materials, niobium materials, and zirconium materials by the same or equivalent method.

In the above embodiments, plasma is generated in the atmosphere only by irradiating the surface of the metal material with the pulsed laser beam, but the present invention is not limited to this. For example, an electric field may be applied to plasma to enhance the brightness of plasma generated by pulsed laser light. By increasing the brightness of the plasma generated in the atmosphere, the thickness of the nitride film can be increased because the instantaneous melting range reaches a deeper portion. In order to apply an electric field to the plasma, the nitride film forming apparatus 1 may be configured as follows.

As shown in FIG. 7, the nitride film forming apparatus 1 is connected to a pair of electrodes 19a arranged so as to sandwich the irradiation path of the laser beam condensed by the converging optical system 12, and the pair of electrodes 19a. and a voltage source 19b that produces an electric field that enhances the plasma generated between the pair of electrodes 19a. Although each electrode 19a can be of any shape and material, for example, it is a rod-shaped electrode made of tungsten. The distance between the electrodes 19a is, for example, within 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, several kV). It is preferable that the electric field value generated in space by the voltage source 19b is, for example, 500 kV/m or more.

The electric field generated between the pair of electrodes 19a must be applied at least when plasma is generated by laser irradiation. If this condition can be satisfied, a continuous electric field or a pulse electric field may be used. When a pulsed electric field is applied, the pulse width of the pulsed electric field is preferably in the range of 1 msec to 100 msec, for example, considering the duration of plasma. In addition, by connecting the voltage source 19b to the control device 14 and causing the control device 14 to control the timing of generating the pulse electric field, the pulse electric field generated between the pair of electrodes 19a is controlled by the pulse laser light from the pulse laser light source 11. may be synchronized with the emission of Specifically, for example, a pulse electric field may be applied at the same frequency as that of the pulsed laser light and with a pulse width that includes a period from immediately before the pulsed laser light is emitted to immediately after the pulsed laser light is emitted.

In the above embodiment, the focusing optical system 12 separate from the pulse laser light source 11 focuses the pulse laser light from the pulse laser light source 11, but the present invention is not limited to this. For example, a converging optical system (for example, a convex lens) may be arranged inside the pulsed laser light source 11 to converge the pulsed laser light emitted from the transmissive mirror of the oscillator. Further, the laser energy may be made spatially dense by extracting the beam emitted from the transparent mirror of the oscillator of the pulsed laser light source 11 by narrowing it with an extracting window.

The above embodiments are examples, and the present invention is not limited to these, and various embodiments are possible without departing from the scope of the invention described in the claims. The components described in the embodiments and modified examples can be freely combined. In addition, inventions equivalent to the inventions described in the claims are also included in the present invention.

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

(Example 1)
In Example 1, each sample of the titanium material was repeatedly irradiated with a focused pulsed laser beam, and X-ray diffraction (XRD) was performed on the film formed on the surface of the sample. XRD detects the reflected X-rays reflected by the surface of the sample among the X-rays irradiated to the sample, and confirms at what angle the reflected X-rays strengthen each other. It is a technique to identify compounds that are In Example 1, the number of irradiation times of the pulsed laser beam irradiated to each sample was changed, and by repeatedly irradiating the same portion of the sample with the pulsed laser beam, it was verified what kind of changes occurred on the surface of the sample. The pulse energy of the pulsed laser light was set to 25 mJ. Converted to pulse energy density, it is 300 J/mm ² .

The results of the experiment are shown with reference to FIG. The vertical axis of FIG. 8 is the intensity (number of counts) of reflected X-rays, and the horizontal axis is the angle 2θ. As shown in FIG. 8, the presence of peaks at the angle 2θ corresponding to TiN and Ti ₂ N could be confirmed in any sample, regardless of the number of times of irradiation. Also, the TiN and Ti ₂ N films were the thickest when the number of times of irradiation was 5, and the TiN and Ti ₂ N films did not become thicker even when the number of times of irradiation was increased. From the above, it can be understood that, when the pulse energy density is relatively small, it is preferable to repeat irradiation with pulsed laser light multiple times in order to obtain TiN and Ti ₂ N films having a certain thickness.

Next, the pulse energy of the pulsed laser beam irradiated to the sample was set to 400 mJ (5000 J/mm ² in terms of pulse energy density), and the sample was irradiated with the pulsed laser beam without changing other conditions. As a result, as shown in FIG. 9, it was confirmed that TiN and Ti ₂ N films were formed on all samples regardless of the number of times of irradiation. It was also confirmed that the TiN and Ti ₂ N films were the thickest when the number of times of irradiation was 1, and the TiN and Ti ₂ N films did not become thicker even when the number of times of irradiation was increased. This is probably because, when the pulse energy density is 5000 J/mm ² , part of the nitride film formed by one irradiation is blown away by the second and subsequent irradiations. From the above, it can be understood that when the pulse energy density is relatively high, the thickest TiN and Ti ₂ N films can be formed with one pulse of laser irradiation, and repeated laser irradiation is unnecessary.

(Example 2)
In Example 2, it was verified what kind of change would occur in the film of the sample by changing the pulse energy density of the pulse laser light while keeping the number of pulse laser light irradiations constant. The number of times of irradiation was set to 20 times, and the pulse energy was set to 5 patterns of 25 mJ, 100 mJ, 200 mJ, 300 mJ and 400 mJ. Converted to pulse energy densities, they are 300 J/mm ² , 1250 J/mm ^{2 , 2500 J/mm 2 ,} 3750 J/mm ² and 5000 J/mm ² , respectively. As a result, as shown in FIG. 10, it was confirmed that TiN and Ti ₂ N films were formed on all samples regardless of the pulse energy density.

(Example 3)
In Example 3, it was verified what kind of difference occurred in the film of the sample depending on whether or not the pulsed laser beam was condensed. The pulse energy of the pulsed laser light is 400 mJ, the pulse energy density is 5000 J/mm ² when condensed, and the pulse energy density is 0.005 J/mm ² when not condensed. The number of times of irradiation was 1 for each. As a result, as shown in FIG. 11, TiN and Ti ₂ N films were formed on the sample surface when the pulsed laser beam was focused, whereas when the pulsed laser beam was not focused, TiN and Ti 2 N films were formed. , a _TiO2 film was formed on the sample surface.

After that, the cross section of each sample was observed with a scanning electron microscope (SEM). As a result, as shown in the SEM image of FIG. 12, TiN and Ti ₂ N films with film thicknesses of 2.2 μm, 5.3 μm, and 6.7 μm were formed when the pulsed laser beam was focused. rice field. On the other hand, TiO ₂ films with thicknesses of about 0.51 μm and 0.59 μm were formed without light collection. From the above, it was confirmed that the formation of the TiN and Ti ₂ N films in the air can be realized only when the pulsed laser beam is focused.

(Example 4)
In Example 4, it was verified what kind of difference would occur on the sample surface depending on whether or not the pulsed laser beam was condensed. The pulse energy density is 300 J/mm ² or 5000 J/mm ² , the pulse frequency is 10 Hz, and the pulse width is 5±1 ns. Other conditions are the same as in Example 1. After irradiation with the pulsed laser light, the surface of the sample was photographed using an SEM and a laser microscope, and the state of the surface of the sample was observed.

FIG. 13(a) is an SEM image of the sample surface irradiated with the non-focused pulsed laser beam, and FIG. 13(b) is an SEM image of the sample surface irradiated with the focused pulsed laser beam. Both have a pulse energy density of 5000 J/mm ² . When the pulsed laser beam was not focused, it was flat as a whole, although a large number of micrometer-scale holes were formed. On the other hand, when the pulsed laser beam was focused, a characteristic wavy structure and a large number of fine cracks were randomly formed. The wavy structure and fine cracks are traces of titanium melting. When the pulsed laser beam was condensed, a gently wavy structure was formed even with a pulsed laser beam having a pulse energy density of 300 J/mm ² , but no fine cracks occurred. This difference is believed to be due to the fact that the pulsed laser beam with an energy density per pulse of 300 J/mm ² melts only the surface portion and does not expand the melted region in the depth direction.

FIG. 14(a) is a laser microscope image of the sample surface irradiated with the non-focused pulsed laser beam, and FIG. 14(b) is a laser microscope image of the sample surface irradiated with the focused pulsed laser beam. When the pulsed laser beam was not focused, the sample surface was almost flat, whereas when the pulsed laser beam was focused, grooves and spot-like concave portions were formed. When a non-focused pulsed laser beam is irradiated, the sample surface remains solid, so a normal thermal reaction takes place to form an oxide layer, which is rapidly quenched, resulting in a large number of microscopic structures on the sample surface. It is believed that vacancies are formed. On the other hand, when a focused pulsed laser beam is irradiated, the sample surface melts instantaneously, and the radicalized nitrogen preferentially permeates the molten titanium. It is considered that a TiN film or a Ti ₂ N film is formed on the surface.

1 Nitride Film Forming Device 11 Pulse Laser Light Source 11a Signal Generator 12 Focusing Optical System 13 Moving Stage 14 Controller 15 Suspension Tool 16 Robot Arm 17 Holder 18 Distance Sensor 19a Electrode 19b Voltage Source

Claims (9)

A nitride film forming apparatus for forming a nitride film on the surface of a metal material,
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. Equipped with a pulsed laser light source that repeatedly emits pulsed laser light with a set energy density per pulse,
Nitride film forming equipment. The nitride film forming apparatus is provided on the emission side of the pulse laser light source, and converges the pulse laser light emitted from the pulse laser light source on the surface of the metal material to form a further comprising focusing optics for generating the plasma;
The nitride film forming apparatus according to claim 1. The nitride film forming device is provided on the output side of the focusing optical system and holds the metal material so that the surface of the metal material is positioned at the focal position of the laser beam focused by the focusing optical system. further comprising
The nitride film forming apparatus according to claim 1 or 2. the holding means is a moving stage that moves the metal material with respect to the focusing optical system;
The nitride film forming apparatus further comprises control means for controlling the operation of the moving stage so that the pulsed laser beam irradiated onto the surface of the metal material traces a predetermined trajectory.
The nitride film forming apparatus according to claim 3. The nitride film forming device is
a robot arm that movably supports the pulsed laser light source and the focusing optical system;
further comprising control means for controlling the operation of the robot arm so that the pulsed laser beam irradiated onto the surface of the metal material traces a predetermined trajectory;
The nitride film forming apparatus according to claim 2 or 3. The energy density per pulse of the pulsed laser light irradiated onto the metal material surface is in the range of 1000 J/mm ² to 6000 J/mm ² ,
The nitride film forming apparatus according to any one of claims 1 to 5. The nitride film forming device is
a pair of electrodes arranged to sandwich an irradiation path of the pulsed laser light emitted from the pulsed laser light source;
An electric field is generated between the pair of electrodes, which is connected to the pair of electrodes, respectively, and increases the luminance of plasma generated by irradiating the surface of the metal material with the pulsed laser light emitted from the pulsed laser light source. further comprising a voltage source;
The nitride film forming apparatus according to any one of claims 1 to 6. The metal material is any one of titanium material, steel material, aluminum material, niobium material and zirconium material,
The nitride film forming apparatus according to any one of claims 1 to 7. A nitride film forming method for forming a nitride film on the surface of a metal material,
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. including a step of repeatedly emitting pulsed laser light with a set energy density per pulse;
Nitride film forming method.

Images