JPS6134505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glow discharge treatment method for conductive members, and more particularly to a method of treating conductive members by increasing the temperature using hollow cathode discharge.

A glow discharge surface treatment method, which is a type of surface treatment for metal materials, has been used industrially. A typical example is the ion nitriding method. The ion nitriding method involves introducing a gas body necessary for the treatment into a reduced pressure vessel (hereinafter referred to as the furnace body) whose pressure is reduced to at least 10 ^-1 Torr or less, and installing an electrode so that the product to be treated becomes a cathode ( (The furnace body may be used as a cathode), and a voltage is applied to this from an external DC power source to generate glow discharge and perform surface hardening treatment.
FIG. 1 shows an outline of the ion nitriding process.

Generally, the workpiece 2 serves as a cathode, and the furnace body 1 serves as an anode. The furnace body 1 has a water-cooled structure to prevent various equipment and parts (such as airtight packing) from being overheated due to heating during processing. In the ion nitriding process, while reducing the pressure inside the furnace to at least 10 ^-1 Torr or less in a vacuum evacuation device 9, a processing gas 6 such as hydrogen gas and nitrogen gas or ammonia gas is introduced to maintain a predetermined pressure in the range of 1 to 10 Torr. The nitriding process is performed by applying a voltage of 300 to 1500 V from the DC power supply 3 to generate glow discharge. In Fig. 1, 4 is an anode terminal, and 5 is an anode terminal.
is the cathode terminal, 6 is the gas cylinder, 7 is the gas inlet,
8 is a gas exhaust port to which a vacuum device 9 is connected, 10 is a vacuum gauge terminal, 11 is an optical pyrometer, and 12 is a control panel.

Since the object to be processed is heated by glow discharge energy, no external heat source is required. Therefore, since the surface generating the glow becomes the heating source, the temperature of the object to be treated changes depending on the ratio of the surface to the volume. In other words, if the workpiece is of the same shape and has a relatively simple shape, the temperature will be almost uniform throughout and uniform processing will be possible, but if the workpiece has a complex shape, especially parts with different surface areas relative to volume, the temperature will vary depending on the location even if the workpiece is the same. This has the disadvantage that the concentration and depth of diffused atoms vary greatly, making uniform processing impossible.

In particular, this temperature difference tends to increase when processing at high temperatures. Therefore, in cases such as carburizing or borening, where the treatment temperature is in a higher temperature range than ion nitriding, that is, 700 to 1200°C, it is necessary to raise or maintain the temperature to the high temperature range using only glow discharge energy. This results in poor thermal efficiency, requiring a lot of energy, and a large temperature difference, making it difficult to uniformly cure the required areas. As a solution, there are, for example, a method of performing ion treatment in a conventional vacuum heat treatment furnace, or a method of performing ion treatment while applying high frequency heating from the outside. However, in the former case, the workpiece is heated using a heater such as carbon fiber.
The heating power source requires a high output, and since heating by ions is reduced, the ion impact energy on the processed object is lower than in conventional treatment using only ions, and the amount of ions on the surface is also reduced. Therefore, the structure and control of the device become complicated, the overall energy consumption is large, and the concentration of atoms involved in processing such as cleaning action by ions and surface hardening is also reduced. In the latter case, when many parts are charged into a furnace to be heated by induced current due to high frequency, the temperature heated between individual parts will differ depending on the distance from the high frequency coil, and the same temperature as in the former case will occur. , power supply, and control become complicated. In addition, a large amount of energy is required for the treatment, and there are also drawbacks in terms of ion cleaning effect and control of surface ion concentration.

On the other hand, depending on the intended use of the article to be treated, it may be necessary to perform treatments having multiple functions within the same article, rather than subjecting the entire surface to a surface treatment with the same function. In the above-mentioned ion surface treatment, such a treatment cannot be performed continuously in one process in the same furnace, and is performed in a complicated process.

In the ion surface treatment method, as a method of obtaining partially different surface treatment layers (for example, the depth and hardness of the nitrided layer in nitriding treatment), as shown in Japanese Patent Application Laid-Open No. 47-6956, An additional metal electrode (anode for the workpiece) is placed between the (cathode) and the wall of the vacuum container (anode) via a resistor to the anode power source.
A method is also known in which the potential of this portion is changed to partially change the ion impact energy. In this method, for example, in the case of ion nitriding, additional metal electrodes are provided at parts that require different nitriding, and the potential of these parts is changed by an external circuit to change the ion bombardment energy to the surface parts. The amount of nitrogen adsorbed and diffused is adjusted to form nitrided layers with partially different depths. However, with this method of partially changing the ion bombardment energy using an external circuit, it is difficult to control the bombardment energy, the device becomes complicated, and in practice, nitrogen diffusion is affected by temperature as well as the ion bombardment energy. Therefore, there was a drawback that the depth of the nitrided layer could not be varied over a wide range.

SUMMARY OF THE INVENTION An object of the present invention was to solve the above-mentioned drawbacks of the prior art. A method for glow discharge treatment of materials that uses an ion treatment power source near the product to efficiently heat it to a certain set temperature and process it in whole or in part, and that can significantly save the energy required for heating. The goal is to provide the following.

The present invention excites a predetermined gaseous substance contained in the atmosphere in a reduced pressure atmosphere by glow discharge,
In an ion surface treatment method in which a certain physical or chemical change is caused in the conductive member by colliding with the surface of the workpiece consisting of a conductive member connected to a cathode, each of the single or multiple workpieces is A hollow cathode effect is produced by arranging a product surrounded by an auxiliary cathode that is made up of at least two surfaces other than the electrode whose cathode is the product to be treated and which maintains a constant gap. The present invention relates to a glow discharge treatment method for a conductive member characterized by the following.

Then, at least two parts of the conductive member are treated.
By exposing the conductive member to different types of glow discharge treatment conditions, it is possible to perform a plurality of types of treatments on the conductive member.

Further, by exposing two or more treated parts of the conductive member to different glow discharge treatment conditions, it is possible to provide a single conductive member with parts having multiple types of functions.

The principle of the present invention will be explained below. First, when diffusing atoms from the surface of a workpiece to impart functions such as surface hardening, surface lubrication, corrosion resistance, and fatigue resistance, it is necessary to do so without adversely affecting the workpiece. If the amount and depth of atoms to be diffused or adsorbed have appropriate values, and the surface concentration is kept constant (generally related to the solid solubility limit of the material or the growth rate of the adsorbate), the treatment temperature is important. play a role. Taking surface hardening of steel materials as an example, when surface hardening with nitrogen, it is generally 400~
It is in the range of 700℃. Surface hardening by carburizing using carbon is 700-1100℃, and boron is 800-1100℃.
The temperature reaches 1200℃. On the other hand, surface lubrication by sulfurization using sulfur is 150 to 600°C. As described above, there are appropriate processing temperatures and processing times depending on the atoms to be diffused and the material to be processed. In ionic surface treatment, methods such as using an external heat source can be used to efficiently raise the surface temperature of the object to be treated or to heat it to a partially controlled temperature. A plurality of auxiliary electrodes with approximately the same potential are placed on the cathode side at a predetermined distance from the surface to be treated, and by controlling the pressure of the gas introduced during ion treatment, the gap between the auxiliary cathode and the object to be treated is Alternatively, the process is performed by generating hollow cathode discharge within the auxiliary cathode. Here, the absorption of heat from the workpiece is due to the heat exchange of glow discharge energy, radiant heat from between the workpieces and the electrodes, and the heat loss due to heat release is radial heat, convection of the processing gas, and radial heat from the electrodes. Thermal conduction from the electrodes (outflow from the cooling water of the electrodes), etc. Among these factors, those that can be used to heat the required portion of the workpiece to a predetermined temperature include radiation heat between the auxiliary cathode and the workpiece. This is achieved by setting the cathode spacing at a constant interval, setting the introduced gas pressure to a predetermined value, and causing a hollow cathode discharge between two negative glows. In this case, the ionization density of the gas between the object to be treated and the auxiliary cathode is also increased, and the surface reaction with the target diffusion active atoms is also activated.

In order to effectively carry out this phenomenon, important factors are the distance from the surface of the object to be treated to the auxiliary electrode and the setting of the gas pressure according to the composition of the gas. First, there is the distance from the surface of the workpiece to the auxiliary electrode, which varies depending on the gas pressure. Unless discharge occurs, the desired effect will not occur. This is because the width of the negative glow varies depending on the gas composition and gas pressure, which strongly affects hollow cathode discharge. Furthermore, the negative glow discharge area of the auxiliary electrode, which is closely related to these, must also be considered. Therefore, in general ionic surface treatment, if this distance is less than 0.5 mm, the reaction of the processing gas to the object to be processed tends to be inhibited.
On the other hand, if the distance is 50 mm or more, the effect of the interaction between the glows becomes weaker, and the heating effect of radiated heat from the auxiliary electrode to the processed object decreases, and there is also heat loss to the auxiliary electrode side, resulting in a loss of energy. Therefore, FIG. 2 shows the heating effect of the object to be processed by the auxiliary electrode of the parallel plate cathode. Figure 3 is 2
This is an example in which two cylindrical cathodes are arranged concentrically and a workpiece is placed between them. As an example, as shown in Fig. 2, a part of the object to be processed 2 is placed in the gap between the parallel plate cathodes, which are made up of two parallel plane auxiliary electrodes 13 placed with a certain gap, and these are connected to the cathode. . Parallel surface when using a mixed gas such as nitrogen gas, hydrogen gas, argon gas, methane gas, etc., and generating glow discharge at a gas pressure of 2.5 Torr, and setting the temperature above the workpiece without an auxiliary electrode on the parallel surface to 600℃. The temperature of the workpiece inside the auxiliary electrode was measured. FIG. 4 shows the relationship between the distance of the gap between the auxiliary electrode on the parallel plane and the object to be processed and the temperature. The relationship between distance and temperature varies greatly depending on the ratio of introduced gas, gas pressure, the shape of the material to be treated, the material of the auxiliary electrode and its shape, etc. Looking at the case in Figure 4, when the distance is 0.5 mm or less, the temperature within the auxiliary electrode on the parallel surface is 600°C, which is almost the same temperature as the other glow surfaces. When the distance becomes larger than that, the temperature of the auxiliary electrode portion on the parallel plane rises rapidly, reaching a peak value at a distance of 3 to 7 mm. At this distance, the temperature inside the auxiliary electrode on the parallel plane is more than 1000℃, which is about 400℃ higher than other parts.
The temperature is getting higher than that. As the distance further increases, the temperature difference between them gradually decreases, and at about 50 mm there is no significant difference. As mentioned above, the distance between the parallel plane auxiliary electrode and the object to be processed is preferably in the range of 0.5 to 50 mm. In addition, in this method, the surface of the article to be treated is carburized in the area heated to 700° C. or higher, and carbonitrided in the other area.

Next is the gas pressure, which has an appropriate value depending on the gas mixture ratio and the desired characteristics. For example, FIG. 5 shows an example in which the temperature was determined using the same method as in FIG. 2, with the distance between the parallel plane auxiliary cathode and the workpiece being 1.5 mm, and the gas pressure being varied.
According to the figure, when the gas pressure is maintained below 0.5 Torr, the temperature in the auxiliary electrode on the parallel surface becomes approximately the same as that on the other glow surfaces. On the other hand, when the gas pressure is increased to 0.5 Torr or more, the glow discharge current density in the auxiliary electrode on the parallel plane becomes higher than in other parts, resulting in a temperature difference. In this example, if the gas pressure is maintained at approximately 2.5 Torr, the temperature within the parallel-sided auxiliary cathode can be maintained at approximately 400° C. or more higher than the other portions. Note that this maximum heating temperature or temperature difference can be varied widely depending on the composition of the gas, the structure of the auxiliary cathode, etc. As described above, in this method, the processing pressure is an important factor in order to heat and maintain the whole or part of the product to be processed. Generally 0.1~
It is desirable to fluctuate within a range of 10 Torr.

Other incidental factors in the present invention include the size and material of the auxiliary electrode. First, the size of the auxiliary electrode is preferably such that when the entire object to be processed is heated, the object to be processed can be placed almost inside the auxiliary electrode on a parallel surface. On the other hand, when it is desired to partially heat or perform a different treatment on the object to be processed, it is preferable that the area is large enough to fit inside the auxiliary electrode having substantially parallel surfaces. Next, the material of the auxiliary electrode may be any material as long as it does not adversely affect the surface of the object to be processed during processing.

Furthermore, the shape and structure of the auxiliary cathode are also important factors in order to carry out the present invention effectively. FIG. 6 shows an auxiliary cathode structure obtained by improving the flat plate cathode 13 shown in FIG. 2, one of which is shown. In this case, 13a is the side facing the workpiece, and 13b is the opposite side. In this treatment method, the cathode gap t ₁
is an important factor. Furthermore, it is effective to devise a structure in which the flat plate cathode 13a on the side of the object to be treated is heated to a higher temperature than the cathode 13b, that is, to make the thickness of the cathode 13b larger than the thickness of the cathode 13a. The hollow cathode effect is generated between 13a and 13b and between 13a and the workpiece. Further, the structure of the auxiliary cathode may be a cylindrical structure having a circular center as shown in FIG. In this case, the auxiliary electrode 13a or 13d is 1
By making it thinner than 3b or 13e and attaching it to 13c as a small piece, it is possible to reduce changes in the gap between hollow cathode discharges due to deformation due to thermal expansion due to heating by hollow cathode discharges. Next is the gap t ₂ and t ₃ between the auxiliary electrodes,
In general ionic surface hardening treatment, if this distance is less than 0.5 mm, the reaction of the processing gas to the treated object tends to be inhibited, while if it is more than 50 mm away, the influence of the hollow cathode effect between glows is reduced. This weakens the heating effect due to radiant heat between the auxiliary electrodes or the object to be treated, and it becomes similar to general ion surface treatment.

Here, a glow discharge is generated at a pressure of 3 Torr using a mixed gas of nitrogen gas, hydrogen gas, argon gas, and methane gas. If there is no auxiliary electrode, the auxiliary electrode shown in Figures 6 and 7 is used. When ₁ is set to 30 mm and the gap between 13a and the workpiece is arbitrarily changed, and when _t2 and _t3 are arbitrarily changed to 10mm and the gap between this and the workpiece is set to 10mm in Fig. 7. Diameter 15mm
The temperature of test pieces with a length of 50 mm was measured by simultaneously processing them in the same furnace. FIG. 8 is a graph showing the relationship between the gap and temperature. The temperature of conventional glow discharge alone without an auxiliary electrode is 570℃ as in A, but
When the auxiliary electrode shown in FIG. 6 is used, it becomes as shown in B and is heated to a temperature of 900 DEG C. or more between 2 and 7 mm where hollow cathode discharge occurs. Furthermore, when the auxiliary electrode shown in Figure 7 is used, the temperature becomes as shown by curve C in Figure 8, which is more than 300°C higher in the hollow cathode discharge area than in the case without the auxiliary electrode. . This temperature difference varies greatly depending on the gas composition, gas pressure, material, shape, thickness, etc. of the auxiliary electrode. As mentioned above, in order to heat each individual component or a specific position of each component using hollow cathode discharge using an auxiliary electrode, the distance at which the hollow cathode discharge is generated is preferably in the range of 0.5 to 50 mm. I understand. Next, regarding the structure of the auxiliary electrode, if a similar experiment is performed with the structure shown in FIGS. 6 and 7, and the cathode 13b on the surface facing the anode is made thicker than the cathode 13a on the side to be treated, each thickness will be Although it depends on the difference in thickness, the thicker the cathode 13a is, the smaller the temperature difference is for the same power consumption, and a structure in which the temperature of the cathode 13a is higher than that of the cathode 13b was obtained.

Examples of the present invention will be described in detail.

[Example 1] Workpieces 2 to be treated are arranged in a concentric ring shape inside the ion surface treatment apparatus shown in FIGS. 9 and 10, and auxiliary electrodes 1 with concentric ring-shaped parallel surfaces are arranged on the inner and outer peripheries.
3 was set, and ion carburizing treatment was performed.

48 chrome-molybdenum steel pinions (diameter 25 mm, length 50 mm, module 2) of JIS standard SCM415 were used as the objects to be treated. The annular auxiliary electrode is
14 installed on the outer circumference is made of SS41 with a diameter of φ200 mm (inner diameter), and 15 installed on the inner circumference has a diameter of φ80 mm (outer diameter), a height of 110 mm, and a wall thickness of 6 mm.

The process involves reducing the pressure inside the vacuum vessel 1 to 10 ^-2 Torr or less, introducing hydrogen gas in that state to create a hollow cathode effect between the pinion and the large and small annular auxiliary electrodes, and heating it at 980°C for 5 minutes. Spatter cleaning was performed, and then nitrogen gas, methane gas, and argon gas were added and carburization was performed by maintaining the same temperature for 10 minutes. The temperature distribution during this treatment was measured using an infrared pyrometer. The temperature distribution during the treatment of the present invention was ±7°C. After the treatment, the treated product was cooled in a furnace, and its cross-sectional hardness distribution was measured. FIG. 11 shows the hardness distribution. In FIG. 11, curves a and a' are the hardness distribution after the treatment according to the present invention, where curve a is the tooth tip and curve a' is the tooth bottom.
Curves b and b' are the hardness distributions after treatment by the conventional method, where curve b is at the tooth tip and curve b' is at the tooth bottom.
As is clear from the figure, in the conventional method, the temperature at the tooth tip is high and the effective hardening depth is 1.5 mm, but the surface hardness at the tooth bottom is low and the effective hardening depth is 0.4 mm. As described above, in the conventional method, it was not possible to obtain a uniform carburized layer on pinions and the like. On the other hand, according to the present invention, the effective hardening depth was 1.3 mm at the tooth tip and 0.85 mm at the tooth bottom, and the surface hardness was approximately Hv800 in both cases, making it possible to obtain a uniform carburized layer. From the above results, according to the method of the present invention, the temperature of the tooth tips and tooth bottoms of a large number of complex-shaped pinions can be maintained uniformly in a high temperature range. On the other hand, the amount of discharge power required for the treatment is 1/3 of the conventional method, so it is extremely effective in terms of resource and energy conservation.

[Example 2] Using the same workpiece as in Example 1 and changing the annular auxiliary electrode in various ways, a mixed gas of nitrogen gas, hydrogen gas, argon gas, and methane gas was mixed in the apparatus shown in Fig. 9. The temperature of the processed product was measured when the pressure was varied. The shape of the annular auxiliary electrode is the sixth
Diameter 0.5 at 13a in the shape shown in Figures and Figure 6
It has a ~9mm hole and a 0.5~9mm wide slit. The gap between the annular auxiliary electrode 13a installed on the outer and inner peripheries and the workpiece is 15 mm.
constant, and the annular auxiliary electrodes 13a and 13
The gap t _i of b is 5 mm. FIG. 12 shows the relationship between gas pressure and temperature distribution. In order to stably perform surface treatment using ions, it is important that the temperature of the object to be treated does not vary greatly even with slight fluctuations in gas pressure. With a single annular auxiliary electrode, the temperature is high within a relatively narrow pressure range only within a range where hollow cathode discharge is generated between the electrode and the workpiece, as shown by curve D in FIG. This is the 6th
If you do it as shown in the figure, it will look like curve E in Figure 12, and the hollow cathode effect will be in the electrode 13 in Figure 6.
It occurs between a and 13b, and its effect can be seen. Further, when holes 13a with diameters of 1 to 3 mm are provided in the correct order, the pressure range at maximum heating becomes wider as shown by curve F in FIG. In this case, a hollow cathode discharge is generated in the hole of the auxiliary electrode 13a according to the pressure due to the fluctuation of pressure, and the pressure range of the hollow cathode discharge with the workpiece is thereby widened. The maximum heating temperature and the pressure range that can maintain a constant temperature depend on the shape and structure of the auxiliary electrode,
It can vary widely depending on the gas composition.

Next, as an electrode with the structure shown in Figure 6, a diameter of 0.5 to 3
The size of the holes was investigated using an internal auxiliary electrode in which holes of 4, 5, 6, 7, 8, and 9 mm were sequentially provided. As a result, it was found that when the maximum hole diameter was 4 mm or more, the maximum heating temperature decreased rapidly, and when the maximum hole diameter was 8 mm or more, the effectiveness decreased significantly. The most effective range is 0.5 to 4 mm in diameter, and a range of 0.5 to 7 mm is also somewhat effective. Next, instead of a hole, length 20mm
A slit was provided. In this case as well, if the width of the slit was within 4 mm, a similar discharge occurred within the slit based on the hollow cathode effect. Next, a similar experiment was conducted with a ceramic layer provided on the outside of the electrode. As a result, it was found that if ceramic was provided on the opposite side of the object to be treated using an electrode having the shape shown in FIG. 6, the electrical output could be reduced by approximately 10%.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the ion nitriding treatment equipment, Figure 2 is an explanatory diagram of the auxiliary electrode of parallel plate electrodes, and Figure 3 is the
Figure 4 is an explanatory diagram of the relationship between the distance and temperature between the object to be treated and the parallel plate cathode by the method of Figure 2, and Figure 5 is also an illustration of the relationship between pressure and temperature. Figure 6 is a perspective view of the improved parallel plate cathode in Figure 2, Figure 7 is a plan view of the electrodes in Figure 6 arranged in a ring, and Figure 8 is a graph of the relationship between the gap and temperature. , FIG. 9 is a vertical cross-sectional view of an apparatus for carrying out the ion surface treatment method of the present invention, and FIG.
FIG. 11 is an explanatory diagram of the relationship between distance and hardness, and FIG. 12 is an explanatory diagram of the relationship between gas pressure and temperature. 1...furnace body, 2...product to be treated (cathode), 4...
Anode terminal, 5...Cathode terminal, 7...Gas inlet,
8...Gas exhaust port, 9...Vacuum device, 13...Parallel cathode, 13a...Auxiliary cathode (workpiece side), 1
3b...Auxiliary cathode (opposite side of processed item), 13c
... Auxiliary cathode (middle part), 131 ... Circular auxiliary electrode (outer periphery), 132 ... Annular auxiliary electrode (inner periphery).

Claims (1)

[Claims] 1. A predetermined gas substance is excited and ionized by glow discharge in a reduced pressure atmosphere, and the ionized material is caused to collide with the surface of a workpiece made of a conductive member connected to a cathode to perform surface treatment. In the method, at least two auxiliary cathodes are installed around the object to be processed so as to face each other, and the distance between the auxiliary cathode and the object to be processed is 0.5.
~50mm, and the gas pressure in the reduced pressure atmosphere is 0.1
10 Torr, and generates glow discharge on both the object to be treated and the auxiliary cathode to perform surface treatment. 2. The ion surface treatment method according to claim 1, characterized in that at least two of the auxiliary cathodes are placed facing each other around a part of the object to be treated. 3. In claim 2, the article to be treated is exposed to at least two types of glow discharge treatment conditions by using a mixed gas of nitrogen gas, hydrogen gas, argon gas, and methane gas as the gas substance. Characteristic ionic surface treatment method. 4. A method in which a predetermined gaseous substance is excited and ionized by glow discharge in a reduced pressure atmosphere, and the ionized material is caused to collide with the surface of a workpiece made of a conductive member connected to a cathode to perform surface treatment. At least two auxiliary cathodes with a multilayer structure are installed around the product so as to face each other, and a gap is provided between the layers of the multilayer structure, and each layer is connected to the cathode, and the innermost wall surface of the auxiliary cathode with the multilayer structure and the product to be treated are The distance between the
and the gas pressure in the reduced pressure atmosphere is 0.1~
10Torr, and surface treatment is performed by generating glow discharge on both the article to be treated and the auxiliary cathode. 5. The ion surface treatment method according to claim 4, characterized in that the auxiliary cathode having a multilayer structure has an interlayer gap of 0.5 to 50 mm.