JP3236636B2 - Method of coating hard compound film on stainless steel substrate surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a surface of a stainless steel substrate with a hard compound film such as tantalum carbide or titanium nitride, and to a method for forming an underlayer for improving adhesion.

[0002]

2. Description of the Related Art When a hard compound film made of carbide or nitride is coated on the surface of stainless steel, argon ion bombardment is performed as a pretreatment for improving adhesion. This treatment is a passivation film (a naturally formed oxide film) formed on the surface of stainless steel.
This is an effective means in many cases. On the other hand, when the hard compound film is coated on the surface of the stainless steel base material, a layer composed of a single metal constituting the compound is coated as a base layer, and then a gas containing carbon or nitrogen is introduced to react. Forming a carbide film or a nitride film of the metal by an ion plating method is performed.

[0003]

The bombardment treatment and the insertion of a single metal layer in the above prior art are effective means, respectively, and these treatments can be used together, but the adhesion is insufficient for some purposes. May be. Accordingly, an object of the present invention is to dramatically improve the adhesion between a stainless steel substrate and a hard compound film coated on the surface thereof.

[0004]

According to the present invention, a chromium oxide film having a thickness of about 20 nm is formed on a surface of a chromium-containing stainless steel substrate by a bombardment treatment in a reduced-pressure atmosphere containing oxygen and argon gas. (C
An oxide layer mainly composed of (r ₂ O ₃ ) is formed, and then an ion plating method is performed in a reduced pressure atmosphere in which an argon gas is introduced. A hard compound film made of a carbide or nitride of the metal was coated by introducing a kind of metal belonging thereto and subsequently introducing a hydrocarbon gas or a nitrogen gas.

[0005] The conventional bombardment treatment removes an oxide film on the surface of a substrate, but the adhesiveness may be improved by positively interposing the oxide film. As an intermediate layer interposed between the metal coating layer and the stainless steel substrate, chromium oxide (Cr ₂
O ₃ ) film is effective. It is appropriate that the film thickness is about 20 nm, which is much thicker than the passivation film (about 0.5 nm). Further, the chromium oxide film is most effectively formed not by simple thermal oxidation in an oxygen atmosphere but by bombardment in a reduced-pressure atmosphere containing oxygen and argon gas.
The present invention has been made based on such findings.

[0006]

When a negative voltage is applied to a stainless steel substrate in a reduced-pressure atmosphere in which a mixed gas of oxygen and argon is introduced, a bombardment treatment is performed to form an oxide mainly composed of chromium oxide on the surface of the substrate. And the phenomenon of removing oxides occur simultaneously. In this case, when the oxygen partial pressure and the accelerating voltage are appropriately adjusted, the oxide having a weak bonding force at the interface is removed, and only the oxide having a strong bonding force grows as an oxide film having excellent adhesion. Such an oxide film fulfills the function intended by the present invention.

[0007]

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view schematically showing a layer structure in an embodiment of the present invention. A mixed gas consisting of 10% oxygen and 90% argon was introduced into a vacuum device to reduce the pressure to 2 × 10
Hold at ⁻³ Torr, apply a negative voltage of −500 V to the substrate made of stainless steel (SUS27), perform bombardment treatment for about 10 minutes, and apply chromium oxide (Cr ₂ O ₃ ) to the surface of the stainless steel substrate 1. An oxide layer 2 having a thickness of about 20 nm was formed. Next, titanium is melted and evaporated by electron beam in an argon gas atmosphere, and a metal titanium layer 3 having a thickness of about 100 nm is coated by a high-frequency excitation ion plating method.
A 4 nm thick titanium nitride layer 4 was coated by a reactive ion plating method.

[0008]

COMPARATIVE EXAMPLE 1 Pure argon gas containing no oxygen was introduced into a vacuum apparatus, kept at 2 × 10 ⁻³ Torr, and a negative voltage of −1000 V was applied to a stainless steel substrate to perform bombarding for about 5 minutes. Then, the passivation film naturally formed on the surface of the substrate was removed. Subsequently, a metal titanium layer and a titanium nitride layer were coated in the same manner as in Example 1.

[0009]

Comparative Example 2 The same oxygen-argon mixed gas as in Example 1 was introduced into a vacuum device and maintained at 5 × 10 ⁻³ Torr.
A thermal oxide film mainly composed of chromium oxide having a thickness of nm was formed.
Subsequently, a metal titanium layer and a titanium nitride layer were coated in the same manner as in Example 1.

Table 1 shows the results of a scratch test on the adhesion of the hard compound films, ie, titanium nitride films, obtained in Example 1, Comparative Examples 1 and 2. The interposition of a thermal oxide film (Comparative Example 2) had no effect in improving the interface adhesion, and the adhesion was improved by removing the passivation film by bombardment (Comparative Example 1). It is clearly observed that the adhesion is further improved by the method of the invention.

[0011]

[Table 1]

[0012]

EXAMPLE 2 An oxide film mainly composed of chromium oxide was formed on the surface of a stainless steel substrate by bombardment treatment in the same manner as in Example 1, and a metal tantalum layer was formed thereon by ion plating in an argon gas atmosphere. And a hydrocarbon gas was introduced to coat the tantalum carbide layer by a reactive ion plating method. Also in this case, extremely strong adhesion was observed.

[0013]

In the above embodiment, the hard compound film is coated with titanium nitride or tantalum carbide.
The method of the present invention is effective for carbide or nitride coatings of metals belonging to Groups IVa, Va and VIa of the Periodic Table. ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness of a hard compound film improves remarkably, it is possible to perform pre-processing by a series of processes using the same vacuum apparatus, The surface treatment method has a special effect.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a layer structure in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel base material 2 Oxide layer 3 Metal titanium layer 4 Titanium nitride layer

Claims (1)

(57) [Claims] 1. A bombardment treatment is performed by applying a voltage to a substrate in a reduced-pressure atmosphere containing oxygen and argon gas, and a chromium oxide (Cr ₂ O ₃ ) having a thickness of about 20 nm is mainly formed on the surface of the stainless steel substrate. Is formed, and then a kind of metal belonging to Group IVa, Va, or VIa of the periodic table is coated by an ion plating method in a reduced pressure atmosphere into which an argon gas is introduced, and then a hydrocarbon gas or a nitrogen gas is applied. A method for coating a hard compound film on a surface of a stainless steel substrate, wherein a hard compound film made of a carbide or nitride of the metal is coated by introducing a gas.