JPS591791B2 - Metal carbide film coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating a metal carbide film on a high melting point metal substrate, and more specifically, a method for coating a metal carbide film on a high melting point metal substrate by a physical vapor deposition method using high frequency glow discharge. Regarding improvements.

Conventionally, in order to provide corrosion resistance to metal materials in contact with molten metal and wear resistance to tools, etc., ceramic films such as vanadium carbide and titanium carbide have been coated using chemical vapor deposition or physical vapor deposition. ing. However, coatings obtained by conventional methods cannot be applied to high melting point metal substrates (
The adhesion to the substrate (hereinafter simply referred to as the substrate) is poor, and the film tends to peel off, especially when the film is thicker than 10 μm.

In recent years, coating the first wall component facing the plasma with a light element compound film such as titanium carbide has attracted attention as a countermeasure against impurities in tokamak-type fusion reactors. In this case as well, a strong and relatively thick coating is required that can maintain sufficient adhesion under the thermal cycles associated with the periodic operation of the fusion reactor. The present invention overcomes the drawbacks of conventional methods and provides a method for coating a substrate with a metal carbide film that has strong adhesion and is difficult to peel off even in thick films.

Instead of maintaining the substrate temperature at a constant evaporation temperature from the start of coating in the conventional method, the present invention increases the temperature of the substrate from room temperature at a constant heating rate of 40 to 200°C/minute at the start of coating. Either the temperature of the substrate is raised to the upper limit temperature of the decomposition reaction, or the coating is performed while thermally cycling between the upper limit temperature of the pyrolysis reaction and its lower limit temperature at the start of coating, and then the temperature of the substrate is maintained at the upper limit temperature of the pyrolysis reaction and the coating is applied. By completing the project, the objective was achieved.

The method of the present invention will be explained based on the ion blating method.

The ion blating device is provided with a program temperature control device that can control the temperature according to a preset temperature increase program by directly applying electricity to the substrate metal or by using an external heating method. Metals such as Ti and V are melted and vaporized by electron beam bombardment. On the other hand, a hydrocarbon gas such as acetylene is introduced into the apparatus through a leak valve until the total pressure is 10 -1 to 10 -2 Torr and a stable glow discharge occurs. high frequency'
A glow discharge of a gas mixture of metal vapor and hydrocarbon gas is started. Then, at the same time as opening the shutter provided directly below the board, temperature control of the board is started according to a preset program. The temperature control of the board is
Do it in one of the following ways:

1) Temperature at which the thermal decomposition reaction of hydrocarbon gas significantly progresses during glow discharge, for example, 800-1 for acetylene gas.
After heating from room temperature to the upper limit temperature at a constant heating rate of 40 to 20[deg.]C/min, the upper limit temperature is maintained at 000[deg.] C. until the coating is completed.

The reason why the temperature increase rate was limited to 40 to 200°C/min is as follows. That is, when coating a metal carbide with a thickness of 20 to 30 μm, the thickness of the interface control layer according to the present invention is 1A of the film thickness.
It needs to be 0% to %. If the layer is thinner than %o, the effect of improving adhesion will be reduced, and if it is thicker than %o, the inherent properties of the carbide layer, such as hardness and corrosion resistance, will be inferior. On the other hand, under normal vapor deposition conditions, it takes about 60 to 100 minutes to produce a carbide film having a stoichiometric composition of 20 to 30 μm. Therefore, in order to secure the above-mentioned interface layer, it is necessary to carry out an interface control operation for 5 to 20 minutes at the initial stage of coating. Therefore, the thermal decomposition of acetylene gas under glow discharge is 80%
It progresses significantly between 0 and 1000℃, so the temperature increase rate is 40℃.
~200°C/min is suitable.

2) The lower limit temperature is set to a low temperature at which hydrocarbon gas decomposition does not significantly proceed, and after applying a thermal cycle between the upper limit temperature and the lower limit temperature to the substrate, the upper limit temperature is maintained until the coating is completed.

For the same reason in the heating rate mentioned above, the initial 5
Apply a substrate heating cycle for ~20 minutes.

In the case of using acetylene gas, there is a temperature difference of 300°C between the lower limit temperature of 500°C and the upper limit temperature of 800°C at which thermal decomposition significantly proceeds. This is repeatedly heated and cooled at a heating and cooling rate of 40 to 200°C/min. Therefore, after 1 to 7 heating cycles, the temperature is maintained at, for example, 800°C. As mentioned above, the composition of the film near the interface between the film and the substrate can be determined by taking advantage of the fact that the dissociation of hydrocarbon gas during low-pressure glow discharge and the thermal decomposition reaction on the substrate depend significantly on the substrate temperature. A metal carbide film with excellent adhesion can be obtained. During this coating, if a negative bias potential of 200 V or more is applied to the substrate, the adhesion can be further improved. The combination relationship between the substrate metal and the metal carbide is such that the metal of the metal carbide forms a total solid solution with the substrate metal, or the metal having a solid solubility limit of several percent or more or the substrate metal inhibits adhesion due to interdiffusion. Any metal that does not form an intermetallic compound can be coated well.

Specifically, the effects of the present invention are recognized in combinations in which a carbide of any of the metals Ti, V, Nb, MO, Ta, and W is used as a coating and any other metal is used as a substrate. .

Although the above method has been explained using an ion plating method, the coating can be similarly obtained by a physical vapor deposition method using high frequency glow discharge such as a sputtering method.

In addition to acetylene, other hydrocarbons that decompose at the deposition temperature can also be used as the hydrocarbon. According to the method of the present invention, a histological examination of a cross section of the coating material after exposure to high temperatures reveals that metal carbides are precipitated in a shape along the substrate interface, and/or metallic elements of the carbides are present. It was found that it was diffused into the substrate metal, resulting in excellent adhesion.

On the other hand, when using the conventional method, the above-mentioned phenomenon was not observed between the coating and the substrate, and the coating was likely to peel off.

Example 1 TiC Coating on Molybdenum Substrate The surface of the molybdenum substrate was polished with emery and washed with acetone, and then attached to a substrate heating device in an ion plating device.

The inside of the ion plating apparatus was sufficiently evacuated, ultra-high purity argon gas was introduced to about 10@-2 T0rr, and about 200 W of power was applied via a high frequency coil provided below the substrate to induce glow discharge. On the other hand, a bias voltage of about -0.6 KV was applied to the substrate, ionized argon was bombarded onto the substrate surface, and the surface was cleaned by sputtering. After that, T
Ti was melted using an electron gun to generate Ti vapor at an evaporation rate of about 0.15 r/min. Acetylene gas 2×10−
A gas partial pressure of 3T0rr was introduced into the apparatus, and a high frequency power of 100W was applied to generate a glow discharge in the mixed gas of Ti vapor and acetylene gas. Then, the substrate was heated and coated using the following method. 1) At the same time as opening the shutter, the temperature control device starts heating up the substrate at a rate of 4°C/min, and when it reaches 800°C, maintain this temperature until the total coating time is 70 minutes, and then completed.

The thickness of the coating was 20-30 μm. 2) For comparison, the coating was similarly completed with the substrate held at 800'C from the beginning.

The results of testing on both of these were as follows.

1) In the case of the film obtained by the conventional method, the film was significantly damaged and peeled off during the usual resin embedding and polishing operations for microscopic observation.

On the other hand, in the case described above, no damage such as peeling was observed in the product obtained by the method of the present invention. 2)
10'C/sec infrared rapid heating, 60'C and 115
When repeated heating at 0° C. was performed 100 times, cracks occurred in the film obtained by the conventional method, but those obtained by the method of the present invention did not suffer any damage.

3) As a result of metallographic examination of the cross section of the coating layer after heating the coating material to 1800°C in a high vacuum, it was found that the coating layer obtained by the method of the present invention has a layer slightly closer to the substrate side along the interface with the base material. It was found that TiC precipitated in a wedge shape and that Ti tended to diffuse toward the MO substrate, giving the appearance of a highly adhesive film.

Example 2 VC coating on molybdenum substrate After cleaning the molybdenum substrate in the same manner as in Example 1,
Panadium was evaporated by an electron gun at a rate of about 0.15 t/min.

Acetylene gas was introduced into the apparatus up to 5×10 −3 T0rr, and a high frequency power of 130 W was applied to start glow discharge. At the same time as the shutter is opened, the substrate temperature control device is activated and the temperature is started to rise at a rate of 7 C/min.
After raising the temperature to 00°C or 1000°C, the temperature was kept constant. A 20 μm VC coating was obtained with a coating time of 70 minutes. When the resulting coating material was repeatedly heated 100 times at 600 DEG C. and 115 DEG C. using rapid infrared heating at 100 DEG C/sec, the coating did not peel off from the substrate, although slight cracks occurred.

In the test described above, when the coating was similarly coated using the conventional method, significant cracks were observed, and there were many places along the cracks where the coating had peeled off.

Example 3 A coating of TiC on a molybdenum substrate was carried out in the same manner as in Example 1 except for the method of controlling the temperature of the substrate.

The substrate temperature was controlled by cycle heating between 500°C and 800°C at 80°C/min for 30 minutes, and then increasing the substrate temperature to 800°C.
With a coating time of 80 minutes, a MOTiC film with a thickness of about 20 μm was obtained. When the coating material was tested, it was confirmed that it was a good coating almost the same as in Example 1. Example 4 TiC coating on tungsten substrate After cleaning the tungsten substrate in the same manner as in Example 1, Ti vapor was generated with an electron gun at an evaporation rate of about 0.15 t/min.

Claims (1)

[Claims] 1 In a method of coating a metal carbide film on a high-melting point metal substrate by a thermal decomposition reaction of metal vapor and hydrocarbon gas using a physical vapor deposition method using high-frequency glow discharge such as an ion plating method or a sputtering method, at the start of coating, The substrate temperature is raised from room temperature to the upper limit temperature of the thermal decomposition reaction at a constant heating rate of 40 to 200 °C/min, or the substrate is coated while being thermally cycled between the upper limit temperature and the lower limit temperature of the thermal decomposition reaction at the start of coating. . A method for coating a metal carbide film, characterized in that the temperature of the substrate is then maintained at the upper limit temperature of a thermal decomposition reaction to terminate the coating.