WO2012153767A1

WO2012153767A1 - Nitriding method and nitriding equipment

Info

Publication number: WO2012153767A1
Application number: PCT/JP2012/061888
Authority: WO
Inventors: 民夫原; 伸明大嶋
Original assignee: 学校法人トヨタ学園; 株式会社プラズマ総合研究所
Priority date: 2011-05-09
Filing date: 2012-05-09
Publication date: 2012-11-15
Also published as: JP6614514B2; JPWO2012153767A1; JP6344639B2; JP2018111884A

Abstract

Proposed is a nitriding method characterized in that nitriding is conducted using a plasma which contains nitrogen atoms.

Description

Nitriding processing method and nitriding processing apparatus

Cross-reference of related applications

This international application claims priority based on Japanese Patent Application No. 2011-104515 filed with the Japan Patent Office on May 9, 2011. All of Japanese Patent Application No. 2011-104515 The contents are incorporated into this international application by reference.

The present invention relates to a nitriding method and a nitriding apparatus for nitriding a metal or the like.

In the fields of automobiles and aircraft, which are our key industries, there is a demand for advanced surface modification and hard film coating in dies and tools in order to respond to urgent issues such as global warming and energy saving. strong.

There is nitriding treatment as surface modification / hard film coating. The nitriding method currently in practical use is a method in which active ammonia gas and ions of nitrogen molecules are accelerated by applying a potential difference to collide with the surface of an object to be processed such as steel. In this nitriding method, when nitrogen molecules collide with the surface of the steel material, the nitrogen molecules are dissociated to generate nitrogen atoms, and nitriding is performed with the nitrogen atoms (see Patent Document 1).

JP 2007-131933 A

In the nitriding method described above, nitrogen atoms react chemically with the steel material to form a thick iron nitride layer on the steel material surface, so that the steel material surface fogging, surface roughness increase, friction coefficient increase, mold release Problems such as deterioration of properties (when using steel as a mold) occur. In addition, since nitrogen molecular ions hardly enter the gap, there is a problem that, for example, nitriding of the narrow slit inner surface cannot be performed.

In one aspect of the present invention, it is desirable to provide a nitriding treatment method and a nitriding treatment apparatus that make it difficult to form a compound layer on the surface of an object to be treated and allow nitriding treatment of a narrow slit inner surface.

The nitriding method of the present invention is characterized in that a processing object is nitrided using a plasma containing nitrogen atoms. According to the nitriding method of the present invention, it is difficult to form a compound layer (for example, an iron nitride layer when the processing target is a steel material) on the surface of the processing target. As a result, problems such as surface fogging, an increase in surface roughness, an increase in friction coefficient, and a decrease in releasability are unlikely to occur on the object to be treated.

Moreover, since nitrogen atoms are neutral and reflect well on the surface of the object to be treated, they can easily enter between narrow slits. Therefore, according to the nitriding method of the present invention, nitriding can be performed on the inner surface of the narrow slit. Furthermore, when the nitriding method of the present invention is applied to a steel material, a surface hardness equal to or higher than that of the conventional method can be obtained.

In the present invention, nitriding means that nitrogen atoms enter and diffuse from the surface of the object to be treated. In the nitriding treatment method of the present invention, it is preferable to use a plasma containing a sufficiently high concentration of nitrogen atoms (atoms) and keep the object to be treated at a high temperature around 500 ° C.

The plasma can be generated, for example, by irradiating a gas containing nitrogen (for example, a gas containing only nitrogen or a gas containing nitrogen as a main component and containing hydrogen or the like) with an electron beam or microwave. By using the above plasma generation method (electron beam excitation plasma method or microwave excitation plasma method), a high concentration of nitrogen atoms can be generated in the plasma.

The potential difference between the plasma potential and the potential of the object to be processed (the potential of the object to be processed is lower than that of the plasma) is preferably 50 V or less. When the potential difference is 50 V or less, one compound layer is hardly formed on the surface of the object to be processed. The potential difference is preferably in the range of 5 to 10V. By being in this range, it is possible to suppress the inflow of electrons contained in the plasma into the processing object.

In the nitriding method of the present invention, the nitriding treatment can be performed in a short time by increasing the concentration of nitrogen atoms in the plasma. Increasing the concentration of nitrogen atoms in the plasma increases the electron density in the plasma. In this case, if the potential difference between the plasma potential and the object to be processed is small, the electron current flowing into the object to be processed increases and the object to be processed is heated. Therefore, in the nitriding method of the present invention, it is preferable to suppress the electrons in the plasma from flowing into the object to be processed. By suppressing the electrons in the plasma from flowing into the processing object, the temperature increase of the processing object can be suppressed. As a method for suppressing the electrons in the plasma from flowing into the processing object, for example, there is a method using a magnetic field applied in the vicinity of the processing object. The direction of this magnetic field is preferably a direction parallel to the surface of the object to be processed.

The nitriding apparatus of the present invention includes a plasma generating unit that generates a plasma containing nitrogen atoms by irradiating a nitrogen-containing gas with an electron beam or a microwave, and a nitriding process that performs nitriding treatment of a processing object using the plasma. A part.

If the nitriding apparatus of the present invention is used, it is difficult to form a compound layer (for example, an iron nitride layer when the processing object is a steel material) on the surface of the processing object. As a result, problems such as surface fogging, an increase in surface roughness, an increase in friction coefficient, and a decrease in releasability are unlikely to occur on the object to be treated.

Moreover, since nitrogen atoms are neutral and reflect well on the surface of the object to be treated, they can easily enter between narrow slits. For this reason, if the nitriding apparatus of the present invention is used, nitriding on the inner surface of the narrow slit becomes possible. Furthermore, when the surface of the steel material is nitrided using the nitriding apparatus of the present invention, a surface hardness equal to or higher than that of the conventional method can be obtained.

The nitriding apparatus of the present invention preferably includes a suppressing unit that suppresses electrons in the plasma from flowing into the object to be processed. By suppressing the electrons in the plasma from flowing into the processing object, the temperature increase of the processing object can be suppressed. An example of the suppression unit that suppresses the electrons in the plasma from flowing into the processing object includes a means for applying a magnetic field in the vicinity of the processing object and suppressing the inflow of electrons by the magnetic field. The direction of this magnetic field is preferably a direction parallel to the surface of the object to be processed.

2 is an explanatory diagram illustrating a configuration of a nitriding apparatus 1. FIG. FIG. 2A is a photograph of the processing object X, and FIG. 2B is a photograph of the processing object Y. It is a graph showing the measurement result of a X-ray diffraction about a process target object. FIG. 4A is a side view seen from the side surface in the longitudinal direction, FIG. 4B is a side view seen from the side surface in the short direction, and FIG. 4C is a perspective view. It is. It is a graph showing the relationship between the distance from an edge and Vickers hardness about the process target object 100. FIG. 2 is an explanatory diagram illustrating a configuration of a nitriding apparatus 201. FIG.

1, 201 ... Nitriding treatment device, 3, 203 ... Chamber, 5 ... Cathode, 7 ... Preliminary anode, 9 ... Anode, 11 ... Accelerating electrode, 13 ... Argon introduction , Nitrogen inlet, 17, 213 ... vacuum exhaust port, 19 ... initial discharge formation region, 21, 215 ... reaction chamber, 23, 100 ... object to be treated, 25 ... conductive wire, 27 ... argon plasma, 29 ... electron beam, 31 ... plasma, 101, 103 ... plate member, 105, 107 ... spacer, 109, 111, 113 .... Cover member, 115 ... slit, 117 ... side, 205 ... quartz glass window, 207 ... processing object holder, 209 ... waveguide

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
1. Configuration of Nitriding Apparatus 1 The configuration of the nitriding apparatus 1 will be described with reference to FIG. The nitriding apparatus 1 includes a cathode 5, a preliminary anode 7, an anode 9, and an acceleration electrode 11 in a chamber 3. The chamber 3 is provided with an argon inlet 13, a nitrogen inlet 15, and a vacuum exhaust 17. In the chamber 3, a region sandwiched between the cathode 5 and the auxiliary anode 7 and facing the argon inlet 13 is an initial discharge formation region 19. In the chamber 3, a portion on the right side of the acceleration electrode 11 and facing the nitrogen inlet 15 and the vacuum exhaust port 17 is a reaction chamber 21.

Here, the correspondence between words is explained. The cathode 5, the preliminary anode 7, the anode 9, the acceleration electrode 11, the argon inlet 13, and the nitrogen inlet 15 correspond to an example of a plasma generation unit. The reaction chamber 21 corresponds to an example of a nitriding unit.

2. Nitriding Method Using Nitriding Apparatus 1 A nitriding method using the nitriding apparatus 1 will be described with reference to FIG. First, the processing object 23 is installed in the reaction chamber 21. Nitrogen gas is introduced into the reaction chamber 21 from the nitrogen inlet 15. A conductive wire 25 is wound around the processing object 23 in a coil shape. At this time, the conductive wire 25 is prevented from contacting the surface of the processing object 23. Both ends of the conducting wire 25 are connected to a power source (not shown), and a current can flow through the conducting wire 25. When a current flows through the conductor 25, a magnetic field is generated in a direction along the surface of the processing object 23 (in the direction of arrow A in FIG. 1). Due to this magnetic field, even if the potential difference between the processing object 23 and the plasma 31 described later is small, it is possible to suppress the electrons in the plasma 31 from flowing into the processing object 23.

Next, argon gas is introduced into the initial discharge formation region 19 from the argon inlet 13 to generate a discharge between the cathode 5 and the auxiliary anode 7. Thereafter, discharge is transferred between the cathode 5 and the anode 9 to generate a stable argon plasma 27. From the argon plasma 27, only the electrons are accelerated by the acceleration electrode 11 to generate an electron beam 29, and the electron beam 29 is extracted to the reaction chamber 21.

In the reaction chamber 21, the nitrogen gas is irradiated with the electron beam 29, and the nitrogen gas is efficiently dissociated and ionized to generate a plasma 31 having a high nitrogen atom density. The processing object 23 is included in the plasma 31. The surface of the processing object 23 is nitrided by the plasma 31.

The temperature of the reaction chamber 21 is controlled to an appropriate temperature (400 to 600 ° C.) by a heater (not shown) provided in the nitriding apparatus 1. The energy of the electron beam 29 can be arbitrarily set by the voltage applied to the acceleration electrode 11.

3. Effects of the nitriding method using the nitriding apparatus 1 Tests conducted to confirm the effects of the nitriding method using the nitriding apparatus 1 will be described.
(1) First Test The above-described nitriding method was performed using the nitriding apparatus 1 under the following conditions.

Processing object 23: SKD61 of hot work tool steel
Pressure in chamber 3: 0.2 Pa
Electron beam 29 acceleration voltage: 80V
Current of electron beam 29: 8A
Temperature in reaction chamber 21: 500 ° C
Time of nitriding treatment: 5 hours Bias voltage (potential of the object to be treated 23 based on the potential of the plasma 31): -50V or -5V
Conductor 25 current: ON or OFF
A processing object (hereinafter referred to as processing object X) that has been subjected to nitriding under the condition that the bias voltage is −50 V and the current of the conductor 25 is OFF, and the bias voltage is −5 V and the current of the conductor 25 A processing object (hereinafter referred to as processing object Y) subjected to nitriding under the condition of ON was cut and observed by corroding the cross section with a nital liquid. 2A and 2B show cross-sectional photographs in the observation. The photograph of FIG. 2A is a photograph of the processing object X (bias voltage: −50 V, current of the conductive wire 25: OFF), and the photograph of FIG. 2B is a photograph of the processing object Y (bias voltage: −5 V, current of the conductive wire 25). : ON).

In the processing object X, a slight compound layer called a white layer is formed on the surface, and a diffusion layer in which nitrogen is diffused and is discolored in black is formed below the compound layer. In addition, the thickness of the white layer in the processing object X is significantly thinner than the thickness of the white layer formed by the conventional nitriding method.

On the other hand, in the processing target Y, the white layer is not recognized on the surface, and only the diffusion layer discolored in black is formed. The thickness of the diffusion layer was not different between the processing object X and the processing object Y even when the bias voltage was different.

Further, X-ray diffraction was performed on the processing object X, the processing object Y, and the unprocessed SKD61 (hereinafter referred to as an unprocessed product). The result is shown in FIG.
In the untreated product (indicated as “Untreated” in FIG. 3), only the iron peak is confirmed, whereas in the processing object X (indicated as “bias voltage: −50 V” in FIG. 3), iron and The peaks of Fe ₃ N and Fe ₄ N, which are nitrogen compounds, are confirmed. In the object to be processed Y (indicated as “bias voltage: −5 V” in FIG. 3), the peak of the iron and nitrogen compound is not recognized, and the peak of α iron is broadened. This is because the width of the peak is expanded due to the diffusion of nitrogen between the iron lattices. From the above, it was confirmed that the lower the bias voltage (the lower the ion collision energy), the more the formation of the compound layer can be suppressed.
(2) Second Test Basically, the nitriding method was carried out in the same manner as the first test. However, in the second test, the processing object 100 shown in FIGS. 4A, 4B, and 4C was used as the processing object. 4A is a side view of the processing object 100 as viewed from the side surface in the longitudinal direction, FIG. 4B is a side view of the processing object 100 as viewed from the side surface in the short direction, and FIG. 4C is a processing object. FIG.

The object 100 to be processed has a pair of plate-

like members

101 and 103 made of SKD61 fixed via

spacers

105 and 107, and three sides covered with

cover members

109, 111 and 113 made of copper. It is. A slit 115 having a width corresponding to the thickness of the

spacers

105 and 107 is formed between the pair of plate-

like members

101 and 103, and the slit 115 is a side surface not covered with the

cover members

109, 111, and 113. It is exposed at 117. The dimensions of each part of the processing object 100 are as described in FIGS. 4A and 4B, and the width of the slit 115 is 1 mm.

The Vickers hardness inside the slit 115 was measured for the processing object 100 after performing the nitriding method. The nitriding process is performed under the condition that the bias voltage is −50 V, and the direction of the electron beam 29 is a direction perpendicular to the side surface 117 and entering the slit 115 from the outside as shown in FIG. 4C. . The nitriding treatment was carried out in each of the case where the treatment time was 5 hours, 10 hours, and 20 hours. Further, the hardness was measured at a plurality of points with different distances from the opening (edge) 115a of the slit 115.

Fig. 5 shows the measurement results of Vickers hardness. FIG. 5 also shows the result of the processing object 100 that has not been subjected to nitriding (shown as “unprocessed” in FIG. 5). As is apparent from FIG. 5, the nitriding process is performed to the depth inside the slit 115, and the hardness is increased.

The reason why the hardness has increased to the back in the slit 115 is the influence of nitrogen atoms contained in the plasma 31. Nitrogen atoms have a long average time to recombine with other nitrogen atoms and return to the molecule, and repeatedly collide and reflect on the surface of the processing object 100 (including the inside of the slit 115) until recombination. . As a result, nitrogen atoms can reach the back of the narrow slit 115.

Note that, since the potential of the processing object 100 is lower than the potential of the plasma 31, ions contained in the plasma 31 are attracted to the material surface near the entrance of the slit 115 and recombine there. Therefore, ions cannot penetrate deep into the slit 115.

As shown in FIG. 5, the hardness in the slit 115 is further increased when the nitriding time is as long as 20 hours as compared with the case of 5 hours. It is also possible to obtain uniform hardness in the entire slit 115 by performing nitriding for a longer time.

This experimental result, which is greatly different from the conventional nitriding method, clearly shows that the high concentration of nitrogen atoms plays an important role in the nitriding method of the present invention.
From the above results, according to the nitriding method using the nitriding apparatus 1, the surface roughness can be increased without forming a nitrogen compound layer such as iron on the metal surface such as a tool or a mold. Therefore, nitriding treatment that increases the hardness near the surface is possible. In addition, even in a tool or mold having a slit (fine structure), the inner surface of the narrow slit can be uniformly nitrided.
<Second Embodiment>
1. Configuration of Nitriding Apparatus 201 The configuration of the nitriding apparatus 201 will be described with reference to FIG. The nitriding apparatus 201 includes a metal plate 204 having a plurality of slits 202, a quartz glass window 205 in contact with the metal plate 204, and a processing object holder 207 in a chamber 203. The processing object holder 207 can hold the processing object 23 on its upper surface. Further, the processing object holder 207 includes a heater (not shown) and can heat the processing object 23. Further, the chamber 203 is provided with a waveguide 209 for sending microwaves, a nitrogen inlet 211, and a vacuum exhaust 213. Inside the chamber 203 is a reaction chamber 215.

Here, the correspondence between words is explained. The nitrogen inlet 211, microwaves described later, the metal plate 204, and the quartz glass window 205 correspond to an example of the plasma generation unit. The reaction chamber 215 corresponds to an example of a nitriding unit.

2. Nitriding Method Using Nitriding Apparatus 201 A nitriding method using the nitriding apparatus 201 will be described. First, the processing object 23 is attached to the processing object holder 207 and installed in the reaction chamber 215. The processing object 23 is heated to 500 ° C., and then nitrogen gas is introduced into the reaction chamber 215 from the nitrogen inlet 211. Next, a microwave is introduced from the waveguide 209. The microwaves pass through the metal plate 204 and the quartz glass window 205 having a plurality of slits 202, and generate surface wave plasma on the lower surface thereof. The surface wave plasma acts on the nitrogen gas in the reaction chamber 215 to generate a plasma containing a high concentration of nitrogen atoms in the reaction chamber 215. The surface of the object to be processed 23 is nitrided by the plasma containing high-concentration nitrogen atoms.

Note that the surface of the object to be processed 23 can be cleaned using the nitriding apparatus 201. Cleaning is performed by introducing surface-wave plasma by introducing argon gas or hydrogen gas into the reaction chamber 215 when the processing object 23 is heated to 500 ° C.

3. Advantages of the nitriding method using the nitriding apparatus 201 The nitriding method using the nitriding apparatus 201 can also be used without forming a nitrogen compound layer such as iron on the surface of a metal such as a tool or a mold. The nitriding treatment can be performed to increase the hardness near the surface without increasing the roughness. In addition, even in a tool or mold having a slit (fine structure), the inner surface of the narrow slit can be uniformly nitrided.

Claims

A nitriding method characterized by nitriding a processing object using a plasma containing nitrogen atoms.
The nitriding method according to claim 1, wherein the plasma is generated by irradiating a gas containing nitrogen with an electron beam or a microwave.
3. The nitriding method according to claim 1, wherein a potential difference between the plasma potential and the object to be processed is 50 V or less.
The nitriding method according to any one of claims 1 to 3, wherein electrons in the plasma are suppressed from flowing into the object to be processed.
5. The nitriding method according to claim 4, wherein electrons in the plasma are prevented from flowing into the processing object by a magnetic field applied in the vicinity of the processing object.
A plasma generating unit that generates a plasma containing nitrogen atoms by irradiating a gas containing nitrogen with an electron beam or microwave;
A nitriding section for nitriding a processing object using the plasma;
A nitriding apparatus comprising:
The nitriding apparatus according to claim 6, further comprising a suppressing unit that suppresses electrons in the plasma from flowing into the object to be processed.