JP2000087210A - Plasma spraying method for forming low oxidized sprayed coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the oxidation of sprayed coating film and to improve the quality of the sprayed coating film by using the one obtd. by adding an mixing inert gas with a specified amt. of gaseous hydrogen as powder feeding gas by a plasma spraying method for forming coating film by laminating powder on the object to be thermal-sprayed. SOLUTION: It is preferable that, as powder feeding gas, the one obtd. by adding gaseous hydrogen to inert gas by 3 to 10% volume percent and mixing them. The inside of the internal opening of a convergent-divergent bell shaped anode 2 is provided with a cathode 1, and the space between the anode 2 and the cathode 1 is fed with working gas. Arc discharge is generated on the space between the anode 2 and the cathode 1, and the working gas is made into plasma, which is blown off from the external opening of the anode 2 at a high speed. Powder as a thermal-spraying raw material is blown into the side port of the anode 2 together with powder feeding gas (carrier gas), which is sucked into the plasma flow, is melted by the plasma of high temp. and is collided against the surface of a substrate to form coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying a powder (including granules) into an arc plasma and laminating the powder on an object to be sprayed, that is, on a substrate to form a low-oxidation spray coating. A plasma spraying method.

[0002]

2. Description of the Related Art Generally, an inert gas is used as a working gas (plasma gas) in plasma spraying. The working gas is a mixture of argon as a main gas and helium or a diatomic gas such as hydrogen or nitrogen as an auxiliary gas. The purpose of adding the auxiliary gas to the working gas is to increase the output, that is, to increase the amount of generated heat and the speed of the plasma jet. The addition of the diatomic auxiliary gas to the working gas increases the dissociation voltage, increases the arc voltage, increases the amount of heat generated at the same current, and increases the plasma jet flow rate.

FIG. 1 shows an outline of a longitudinal section of a plasma spraying head. Cathode 1 is located in the inner opening of horn-shaped anode 2 and the working gas is supplied to the space between them. By generating an arc discharge between the anode 2 and the cathode 1, the working gas becomes plasma and the anode 2
Blows out from the outside opening (nozzle) at high speed. The powder, which is a material for thermal spraying, is blown into the side opening of the anode 2 together with a powder supply gas (carrier gas), is sucked by the plasma flow, is melted by the high heat of the plasma, and is melted by the plasma flow on the front substrate. They collide and form a layer. Anode 2 is supplied with cooling water.

The powder to be sprayed is supplied into the plasma flame together with the powder supply gas near the nozzle outlet (FIG. 1) or immediately outside the nozzle. The powder supplied in the plasma flame is exposed to a high temperature and collides with the substrate at a high speed to form a film on the substrate. At this time, an argon gas is generally used as the powder supply gas, and the flow rate is about 4 to 10 liter / min.

[0005]

One of the problems when a film is formed on a substrate by plasma spraying in the air is as follows.
The powder, which is a raw material, becomes hot due to the plasma flame, and the surface may be oxidized before colliding on the substrate. This problem is significant when the powder is metal powder. As a countermeasure, the base material and the space around the spraying head facing it are covered with a chamber or the like, and the atmosphere is shut off by a chamber or the like. There is an atmospheric spraying method in which spraying is performed after replacing with an inert gas. However, since a chamber and a vacuum evacuation device are required, only batch production can be performed, and it is difficult to construct a continuous production mechanism or a preload chamber or the like. This requires large-scale equipment, such as installation of front and rear processes, and is industrially inefficient.

[0006] As for the working gas for generating the plasma flame, hydrogen may be used as the auxiliary gas in some cases. For example, the main gas of the working gas is argon, hydrogen is used as the auxiliary gas,
10 to 20% by volume ratio (50% of main gas argon)
(5 to 10 liter / min). This hydrogen is given high energy by arc discharge when passing between the cathode 1 and the anode 2 and becomes an ionized plasma state, so that the dissociation voltage of the working gas increases and the arc voltage increases. . As a result, the amount of generated heat increases. Since hydrogen is a reducing gas, it has the effect of preventing oxidation and forming a dense, uniform and good thermal spray coating, which helps to improve the above-mentioned oxidation problem.

However, when the powder to be sprayed is a metal powder, particularly a low melting point metal or its alloy powder, the powder becomes overmelted when forming the sprayed coating, and the performance of the sprayed coating is reduced. In particular, there arises a problem that the adhesion strength of the film decreases. For example, if the difference between the thermal expansion coefficients of the base material and the molten powder is large, excessive stress remains between the film and the base material, resulting in a large change in the structure of the film. May peel off. However, a contradiction arises that the original purpose cannot be achieved simply by reducing the amount of hydrogen added.

Further, some metals are sensitive to hydrogen depending on the kind of metal. For example, in the case of nickel and nickel alloys, the formed thermal spray coating is weakened by the influence of hydrogen or the crystal grain boundary is formed after the thermal spray coating is formed. It is also known that hydrogen collects in the vicinity and causes adverse effects such as delayed cracking.

[0009] These problems become remarkable if the powder components are the same, because the finer the powder, the larger the surface area. This has an adverse effect that conflicts with the intention to use fine powder to form a dense film. Therefore, adding hydrogen to the working gas (plasma gas) is an effective method for suppressing oxidation, but has a problem.

An object of the present invention is to improve the above-mentioned problems. More specifically, an object of the present invention is to suppress the oxidation of the thermal spray coating and to realize this without lowering the quality of the thermal spray coating.

[0011]

According to the present invention, powder is supplied to a plasma flame by a powder supply gas in which 3 to 10% by volume of hydrogen gas is added to and mixed with an inert gas.

The addition of hydrogen gas to a powder supply gas containing an inert gas as a main component means that the powder supply gas does not pass between the cathode 1 and the anode 2, so that the powder supply gas The hydrogen in the inside makes the plasma flame injected from the nozzle a reducing atmosphere without affecting the arc discharge conditions, that is, without increasing the plasma arc voltage. As a result, the above-mentioned problem caused by an increase in the plasma arc voltage can be solved, and a sprayed coating with less oxidation can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

EXAMPLES Thermal spraying was performed under the following conditions:

[0014]

[Table 1] The powder supply gas was 3% hydrogen and 7% argon gas.
% And 10%, and powder was fed to the plasma flame. At this time, without forming a sprayed film on the base material,
The sprayed powder (sprayed particles of the examples) exposed to the high temperature was collected.

For comparison, two kinds of powder supply gas were used, one in which hydrogen was added to argon gas at 2%, and the other in which argon was added without hydrogenation at 100%. Then, powder was supplied to the plasma flame. At this time, the sprayed powder (the sprayed particles of the comparative example) exposed to the high temperature was collected without forming the sprayed film on the base material.

FIG. 2 shows the mixing ratio of oxidized particles in the collected molten powder. This mixing ratio indicates the percentage of the number of oxidized particles therein relative to the number of collected particles. Whether the collected particles were non-oxidized or oxidized was determined by visual judgment using a microscope.

FIG. 3 is an enlarged view of the collected particles. In FIG. 3, the surface is smooth and glossy, whereby the center of the sphere appears white due to the reflection of light, and the outside of the center is a non-oxidized round sphere which appears black due to total reflection.
Oxidized particles are irregularly shaped particles having fine irregularities on the surface and appearing rough. In the above determination, the total number of particles is counted, the number of oxidized particles in them is counted,
The calculation of (the number of oxidized particles / the total number of particles) × 100 was performed to calculate the mixed ratio of oxidized particles.

As shown in FIG. 2, when the amount of hydrogen in the powder supply gas is 2% or less, oxidized particles are generated, and the amount of hydrogen is reduced to 3%.
It can be seen that the above eliminates the oxidation of the particles.

Table 2 shows the tensile strength of the thermal spray coating in a direction perpendicular to the coating surface. This test material was prepared by adding 0%, 3% and 7% hydrogen to Angon gas on the end face of a round steel bar having a diameter of 25.4 mm.
%, And thermal spraying was performed under the conditions shown in Table 1 by using three kinds of powder supply gases, and another end face of a round steel bar having a diameter of 25.4 mm was joined to the surface of the thermal sprayed coating with resin. It is a kind of sample material. 3% and 7% hydrogen in Angon gas
It can be seen that the thermal spray coating using the two types of powder feed gas to which (a) is added has a high tensile strength because the powder particles heated by the plasma flame have little oxidation.

[0020]

[Table 2] In Table 3, powder was supplied to a plasma flame under the same conditions as in Table 0 above except that a powder feed gas obtained by adding 7 to 15% hydrogen to Angon gas was used, and a sprayed film was formed on a substrate. Was formed, the sprayed powder exposed to high temperature (sprayed particles of the comparative example) was collected, and the hydrogen content of the sprayed powder was measured by X-ray fluorescence analysis. Table 3 shows the measurement results.

[0021]

[Table 3] From this measurement result, it can be seen that when 10% or less of hydrogen is added to the Angon gas, the sprayed powder does not contain hydrogen.

[0022]

According to the present invention, the quality of the sprayed coating can be improved by suppressing oxidation of the sprayed coating formed in the atmosphere as much as possible and not being adversely affected by hydrogen. When forming a film by plasma spraying of alloys or active materials and carbide-based nitride ceramics, it is possible to form a sound sprayed film without forming an oxide film as much as possible and improve the production efficiency. be able to.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an outline of the structure of a thermal spray head.

FIG. 2 is a graph showing a relationship between an amount of hydrogen added to a powder supply gas and an oxidation ratio of a sprayed powder.

FIG. 3 is an enlarged plan view of a sprayed powder.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Kitahara 7-6-1, Higashi Narashino, Narashino-shi, Chiba Nippon Steel Welding Industry Co., Ltd. (72) Inventor Osamu Ichimura 7 Higashi-Narashino, Narashino-shi, Chiba 6-1-1, Nippon Steel Welding Industry Co., Ltd. (72) Inventor Yoshiji Nishi 1-10-1, Shinsayama, Sayama-shi, Saitama Honda Engineering Co., Ltd. (72) Inventor Keiichi Kikawa Saitama 1-10-1 Shinsayama, Sayama City Honda Engineering Co., Ltd. (72) Inventor Yuji Furuyama 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. F-term (reference) 4K031 AB09 CB35 CB37 CB45 CB46 DA04 EA10

Claims (1)

[Claims] In a plasma spraying method in which powder is supplied into an arc plasma directed to an object to be sprayed, and the powder is laminated on the object to be sprayed to form a film, the powder is supplied as a powder supply gas. A plasma spraying method for forming a low-oxidation sprayed coating, characterized by spraying using a mixture obtained by adding 3 to 10% by volume of hydrogen gas to an active gas.