JPS62130270A - Ceramic coating method - Google Patents

Abstract

PURPOSE:To form a metallic film having excellent corrosion resistance on a base material by coating a metal on the base material then carbonizing or nitriding the metallic film. CONSTITUTION:The film of the metal (for example, Ti) is formed by a CVD method on a substrate consisting of a carbon steel, etc. This film is the assemblage of the columnar crystal extending from the surface of the base material to the film surface. Since there is a defect at the boundary of the adjacent columnar crystals, a pin hole penetrating to the base material is formed. The formed metallic film is carbonized or nitrided by the conventional method to increase the volume thereof for the above-mentioned method. The defect of the film is eliminated by such increase of the volume. The ceramic film which is dense and contains less defects is thus obtd. The structure is made discontinuous and the penetration defects are further decreased if the multi-layered film are formed by repeating such operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a ceramic coating method applied to members requiring corrosion resistance, such as chemical industrial reactors and pumps.

[Conventional technology]

Traditionally, methods for obtaining corrosion-resistant coatings include thermal spraying, plating,
There are methods such as chemical conversion treatment, and metals (e.g. Zn, At, N
i) and ceramics ('riot, At20s, etc.)
The aim was to improve corrosion resistance by coating with this method.

[Problem that the invention seeks to solve]

However, the films produced by these methods
It contained many penetrating defects (hereinafter referred to as pinholes) that reached the underlying layer, so its corrosion resistance was insufficient. On the contrary.

Physical vapor deposition method (PVD method) and chemical vapor deposition method (CVD method)
Ceramic coatings are formed at the atomic or molecular level, resulting in high-performance films with extremely few pinholes. However, although the number of pinholes is extremely small, the presence of pinholes does not mean that the film is completely corrosion-resistant, and cannot be put to practical use in a severe corrosive environment. The inventors.

As a result of investigating the cause of the formation of these pinholes, we found that these pinholes are a collection of columnar crystals in the pVD or CVD film that extend from the surface of the substrate to the surface of the film, as schematically shown in Figure 2. It has been found that since defects exist at the boundaries between adjacent columnar crystals, pinholes are formed that penetrate the base material, and that removing the penetration defects at these boundaries is the biggest problem.

[Means for solving problems]

Therefore, the gist of the present invention is a ceramic coating method characterized in that a ceramic coating film is obtained by coating a metal on a base material and then carbonizing or nitriding the metal film.

[For production]

Eliminating defects at the columnar crystal boundaries means increasing the density of the film to a solid layer. Typically, carbides or nitrides have a lower density than metals. Therefore, carbonizing or nitriding this metal means that the volume increases.

Defects are removed using this volume increase.

That is, by carbonizing or nitriding defects contained in the first coated metal film, the volume of each columnar crystal increases as shown in FIG. 1, and the defects can be removed. or.

If this process is repeated to form a multilayer film, the structure will become discontinuous and the number of through defects will further decrease.

[Example 1] Carbon steel (S45
C) By ion blating the HCD (holocathode) method, which is a type of PVD method, on the substrate.

The Ti film was coated with a thickness of 1 mm.

The coating conditions are as follows.

(I) HCD gun output 45V x 400A (2) Substrate temperature: 500°C After -to, stop the Ti coating, introduce N2 gas into the device, and apply a voltage of -500V to the substrate at a pressure of 0.5 Torr. By causing a glow discharge, the coated Ti film is ion nitrided, resulting in approximately 1.1
A TiN film having a thickness of trrtn was obtained. Next, this Ti
By repeating coating Ti on the N film in the same manner and nitriding in the same manner four times,
A TiN film with a thickness of about 5.5 mm was obtained.

Next, in order to investigate the corrosion resistance of the TiN films with a thickness of 1.1 and 5.5 rran obtained in this way, the results were obtained by immersing them in a 10T HC1 aqueous solution at room temperature.
A film with a thickness of 1.1 rtrm obtained by the conventional method (reactive ion blating) had minute corrosion points detected after 10 minutes, and a film with a thickness of 5.5 mm after 1 hour;
Corrosion of the film obtained by the present invention with a thickness of 1.1 rran was observed after 2 hours, and the film had a thickness of 5.1 rran.
No corrosion was observed in the coating of Tone 5 even after 10 hours.

[Example 2] Using the same substrate as [Example 1], pTici5mm:7-tinting was performed by the conventional CVD method. The coating conditions were as follows.

(1) Furnace temperature: 1ooo℃ (2) Raw material gas: TiC4; 80cc/cm and flow rate CH
4; 80 CC/mr H2; 2 0 0 CC/yrin (3) Furnace pressure: Atmospheric pressure Next, only Tict and N2 gas were flowed to reduce Ti to 2.3
After coating the Ti film, the gas was changed to CH4 and H gas to carbonize the Ti film. By repeating this operation twice, a TiC film with five different thicknesses was formed. As a result of conducting a corrosion resistance test on these coatings in the same manner as in Example 1, corrosion points were observed after 1 hour of immersion in the coatings prepared by the conventional method.

No corrosion was observed in the coating 1-t according to the present invention even after 10 hours.

〔Effect of the invention〕

Ceramic coating according to the invention.

After coating the metal, a dense ceramic film with few defects can be obtained by nitriding or carbonizing the metal.

[Brief explanation of drawings]

Figures 1 and 2 schematically show the effects of the present invention. Figure 1 is a cross-sectional view of a film obtained by the method of the present invention, and Figure 2 is a cross-sectional view of a film obtained by the conventional method. . 1: Columnar crystals in the film, 2: Base material. 0

Claims (1)

[Claims] A ceramic coating method characterized in that a ceramic coating film is obtained by coating a metal on a base material and then carbonizing or nitriding the metal film.