JPH04268061A - Plasma spraying method with mixed composition - Google Patents

Abstract

PURPOSE:To facilitate the combination of dense-dense, dense-porous or porous- porous, etc., for every component by theoretically changing the grain size ratios of granular bodies in the plasma spraying method forming the films of mixed compsns. CONSTITUTION:The average grain size ratio of starting powder is changed with each of the respective components to adjust the molten state, by which the density of the thermally sprayed films is limited. The grain size ratios are determined in accordance with, for example, the time before the completion of melting. The formation of the thermally sprayed film mixture having the mechanical, thermal and electrical properties approximate to the mechanical, thermal and electrical properties of general bulk materials, the limitation of the density for every component and the limitation of the density over the entire part of the films are easily executed over a wide range. Such is suggestive of the expansion of the new field of applications of the plasma spraying method.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention aims at high performance in heat resistance, wear resistance, corrosion resistance, and solid electrolyte fuel cells.
The present invention relates to film quality control when producing a film having a region composed of two or more types of components such as alloys, cermets, and functionally graded materials.

0002

2. Description of the Related Art A film formed by plasma spraying contains many pores. Therefore, the mechanical strength was usually 1/5 to 1/10 that of general bulk materials. Furthermore, in the field of fuel cells, one of the biggest challenges in the field is the low electrical properties, particularly the low ionic conductivity of ZrO2 films formed by thermal spraying. High density thermal spray coatings, which are closely related to various physical properties, are expected from many fields.

[0003] In order to solve this problem, a reduced pressure plasma spraying method was developed in which spraying is carried out under reduced pressure. Density control is based on internal plasma parameters (plasma input, operating pressure,
This is done by optimizing the plasma external parameters (plasma gun structure, powder particle size, substrate position) (e.g., JP-A-63-450, JP-A-1-2273).
No. 62 and others). These optimal parameters strongly depend on the thermal properties of the substance, such as melting point and specific heat. Density control of single composition coatings has been achieved with some success by adjusting the internal parameters described above.

[0004] On the other hand, plasma spraying has been considered as a representative example of the manufacturing process for mixed composition coatings. In particular, this method is positioned as one of the most effective methods for applying functionally graded materials to the engine parts of rockets and aircraft. When forming a mixed composition film by plasma spraying, this method can be roughly divided into two types. One method is to arrange a plasma gun for each substance and perform thermal spraying with a separate gun, and the other is to spray all components with one plasma gun.

[0005]

In the method of arranging a plasma gun for each substance, it is relatively easy to independently control the density of each substance by changing the input for each plasma. However, there are serious problems in film uniformity and equipment. Furthermore, with the method of spraying all the components with one plasma gun, it is extremely difficult to control the density of each material if the optimal internal parameters for each material differ greatly. Therefore, optimization of external parameters can be considered to overcome this problem. For example, Japanese Patent Laid-Open No. 63-201039 discloses a plasma gun that has one hole for powder supply in the plasma gun for each substance, but at present there are two types of plasma guns: one for ceramics and one for metals. The gun structure has only been proposed and is not a complete solution. On the other hand, density control by powder particle size ratio has only been announced in academic conferences and academic papers regarding single composition films (for example, author: R. Mcperson, magazine: Thin
Solid Films, 83 (1981) 297
) do not disclose coating density control by changing the powder particle size ratio for mixed composition coatings.

[0006] Against this background, the present invention provides a mixed composition plasma spraying method in which the powder particle size ratio is theoretically varied and combinations such as dense-dense, dense-porous, or porous-porous are easily achieved for each component. The purpose is to provide

[0007]

[Means for Solving the Problems] The present invention provides a plasma spraying process in which film density strongly depends on the melting state of particles, by adjusting the particle size ratio of raw material powder for each substance when forming a mixed film density. It is characterized by controlling the film density. This particle size ratio is determined using, for example, the time (t) until the particles are completely melted, which is calculated from Equation 1, as an index. This takes advantage of the fact that the density of a film formed by thermal spraying is controlled by the melted state of the particles when they reach the substrate. For example, in order to equalize the film density of each substance, by determining the particle size ratio so that the above time (t) of each substance is equal, the melting state of the particles of each substance is adjusted to be equal, and density control is performed. conduct.

[0008]

[Function] It was very difficult to form a mixed composition film in which all the components were dense using one conventional plasma gun, but the present invention can improve the density of the mixed film by using, for example, the following equation 1. This is to control the properties of the film and achieve diversity in film properties. The time t from room temperature to completion of melting is t=(ρDC
/σα) [log {TO-Tg/Tm-Tg)}+
H/(Tg-Tm)] It can be expressed by Formula 1.

ρ: powder density, D: diameter of starting powder,
C: Specific heat, σ: Molecular weight, α: Heat transfer coefficient of gas, H: Latent heat, TO: Temperature of starting powder, Tg: Average temperature of plasma gas, Tm: Melting point The melting state of particles is changed using this t as an index. , to control film density.

0010

[Example] [Example 1] Y2O3 stabilized ZrO2 (YSZ) and Ni-Cr alloy (Ni-C
(a) Search for the optimal plasma parameters for forming a dense film of YSZ with an average particle size of 27 μm Input = 80 kW, plasma gas flow rate = Ar: 120 l
/min, H2=15l/min, carrier gas flow rate=15l/min, plasma working pressure=200T
ORR, substrate position = 15 cm (b) Find t of YSZ, and calculate D of Ni-Cr so that these values are equal. Under the present conditions, D = 55 μm.

(c) Ni having an average particle size close to D
A mixed composition film was formed using -Cr and the above-mentioned YSZ powder (d) The particle size ratio was 1:2.0. FIG. 1 shows the change in the mixture ratio film density when the Ni-Cr raw powder particle size was changed under the conditions (a). It can be seen that under this condition (a), a dense mixed film can be obtained when the average particle size is 57 μm (the average particle size available at this time). The particle size ratio at this time was 1:2.1, which is almost in agreement with the previous calculation result. In other words, it has become possible to easily form a dense mixed composition film by direct current plasma spraying by adjusting the particle size of the powder used, using the time taken until the particles are completely melted as an indicator.

[0012] Since the influence of the particle size distribution of the powder on the film quality is very important, it is desirable to limit the distribution to within ±20%. Normally, the powder particle size used for thermal spraying is 10-40 μm, making it possible to form a mixed composition coating with higher density than before. [Example 2] When forming a mixed composition coating consisting of dense Ni-Cr and porous YSZ Figure 2 shows the change in density of the mixed thermal sprayed coating with respect to the mixing ratio when the particle size ratio of the starting powder used is changed. shows. Experimental conditions were input = 80kW, plasma gas flow rate = Ar: 120l.
/min, H2=15l/min, carrier gas flow rate=15l/min, plasma working pressure=200T
ORR, substrate position = 20 cm. Type A is dense N
Type B is composed of i-Cr, dense YSZ and Ni-Cr, type B is composed of dense Ni-Cr and porous YSZ, and type C is composed of dense Ni-Cr and porous YSZ.
are porous Ni-Cr and porous YSZ and Ni-Cr
A mixed composition film is formed.

[0013]

[Effects of the Invention] The mechanical strength of coatings formed by plasma spraying is usually less than half that of ordinary bulk materials. The relationship between the thermal spray coating density and Young's modulus of YSZ is a monotonically increasing relationship, and it was possible to form a coating with a Young's modulus 2 to 5 times higher than that of conventional methods by forming a dense coating. FIG. 3 shows the change in Young's modulus when changing the mixing ratio (VOL%) of YSZ and Ni-Cr. There is no example of forming a mixed composition coating in which all of the substances are dense, and the present invention has made it possible to form a mixed thermal spray coating whose mechanical properties are close to those of general bulk materials.

[0014] The present invention makes it possible to form a film in which all the components are dense, and furthermore, it becomes possible to easily control the density of each component and the density of the entire film. Mechanical,
The control of various electrical and thermal properties will also expand, suggesting the expansion of new fields of application for plasma spraying.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the mixing ratio and film density when the particle size ratio is changed (YSZ particle size is constant).

FIG. 2 is a graph showing the relationship between the mixing ratio and film density when changing the particle size ratio.

FIG. 3 is a graph showing the relationship between the mixing ratio and elastic modulus of a dense film.

Claims (2)

[Claims] Claim 1: A method for producing a mixed composition coating consisting of two or more components by plasma spraying, in which the average particle size ratio of the starting powder is varied for each component and the molten state is adjusted. A mixed composition plasma spraying method characterized by controlling density. 2. The mixed composition plasma spraying method according to claim 1, wherein the average particle diameter ratio of each component is set so that the time (t) from room temperature to completion of melting is equal for each component.