JP2947626B2 - Mixed composition plasma spraying method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention aims at high heat, abrasion and corrosion resistance and also for high functions such as solid oxide 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 an alloy, a cermet, and a functionally gradient material.

[0002]

2. Description of the Related Art A coating formed by a plasma spraying method contains many pores. Therefore, the mechanical strength was usually 1/5 to 1/10 as compared with the general bulk material. In the field of fuel cells, low electrical conductivity, particularly the low ionic conductivity of a ZrO ₂ coating formed by thermal spraying, is one of the biggest issues in the field. As described above, increasing the density of a thermal sprayed coating having a close relationship with various physical properties is expected from various fields.

[0003] In order to solve this problem, a low pressure plasma spraying method for performing spraying under reduced pressure has been developed. Density control depends on the internal parameters of the plasma (plasma input, operating pressure,
It is performed by optimizing the gas flow rate) and the external parameters of the plasma (plasma gun structure, powder particle size, substrate position) (for example, JP-A-63-450, JP-A-1-227362, etc.).
These optimal parameters strongly depend on the thermal properties of the substance, such as melting point and specific heat. Controlling the density of a single composition coating has met with some success by adjusting the internal parameters described above.

On the other hand, the application of the plasma spraying method has been considered as a typical example of the production process of the mixed composition film. In particular, this method is positioned as one of the most promising methods as a means for applying the functionally graded material to the engine parts of rockets and aircraft. In forming a mixed composition film by the plasma spraying method, this method can be roughly classified into two methods. One is a method in which a plasma gun is provided for each substance and thermal spraying is performed by separate guns, and the other is a method in which all components are thermally sprayed by one plasma gun.

[0005]

In the method of disposing a plasma gun for each substance, independent control of the density of each substance is relatively easy by changing the input of each plasma.
However, there are serious problems inherent in film uniformity and equipment. Further, in the method of spraying all components with one plasma gun, it is extremely difficult to control the density of each substance when the optimum internal parameters for each substance are greatly different. Therefore, optimization of external parameters can be considered to overcome this problem. For example, Japanese Patent Application Laid-Open No. 63-201039 discloses a plasma gun having a hole for supplying powder in one plasma gun for each substance. The gun structure has been proposed but not a complete solution. On the other hand, density control by powder particle size ratio has been reported in academic conferences and academic papers only for single composition films (eg, author:
R. Mcperson, Magazine: Thin Solid Films, 83 (1981) 29
No. 7) does not disclose control of the film density by changing the powder particle size ratio for the mixed composition film.

In view of the above, the present invention provides a mixed composition plasma spraying method in which the powder particle size ratio is theoretically changed and the combination of dense-dense, dense-porous, porous-porous, etc. is easy for each component. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention provides a plasma spraying process in which the coating density is strongly dependent on the molten state of the particles, by adjusting the raw material powder particle size ratio for each substance when forming a mixed coating density. It is characterized by controlling the film density. The particle size ratio is determined using, for example, the time (t) until the particles calculated from Equation 1 are completely melted, as an index. This is based on the fact that the density of a film formed by thermal spraying is governed by the molten state of the particles when they reach the substrate. For example, in order to make the coating density of each substance equal, the particle size ratio is determined so that the above-mentioned time (t) of each substance becomes equal, and the melting state of the particles of each substance is adjusted to be equal, and the density control is performed. Do.

[0008]

Although it has been very difficult to form a mixed composition film in which all components are dense using a single conventional plasma gun, the present invention uses, for example, the following formula 1 to determine the density of the mixed film. The purpose of this control is to control the characteristics of the film. The time t from the room temperature to the completion of melting is represented by t = (ρDC / σα) [log {TO−Tg / Tm−Tg)} + H / (Tg−Tm)]

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, T
m: melting point Using this t as an index, the melting state of the particles is changed to control the film density.

[0010]

EXAMPLES [Example 1] Y ₂ O ₃ stabilization in which both types are dense
When forming a mixed composition film composed of ZrO ₂ (YSZ) and a Ni-Cr alloy (Ni-Cr) (a) Search for the optimal plasma parameters for forming a dense film of YSZ with an average particle size of 27 μm. 80 kW, plasma gas flow rate = Ar: 120 l / min, H2
= 15 l / min, carrier gas flow rate = 15 l / min, plasma operating pressure = 200 TORR, substrate position = 15 cm (b) t of YSZ, and Ni-
Calculate D of Cr Under the conditions, D = 55 μm.

(C) Ni-Cr having an average particle size close to D
And YSZ powder to form a mixed composition film. (D) The particle size ratio is 1: 2.0. FIG. 1 shows the change in the coating density at the mixing ratio when the particle size of the raw material Ni-Cr is changed under the condition (a). Under the condition (a), it can be seen that a dense mixed film is obtained when the average particle size is 57 μm (the average particle size available this time). The particle size ratio at this time is 1: 2.1, which is almost in agreement with the previous calculation result. In other words, a dense mixed composition film can be easily formed by the DC plasma spraying method by adjusting the particle size of the powder used, using the time until the melting of the particles is completed as an index.

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%. Usually the powder size used for thermal spraying is 10
−40 μm, and a mixed composition film having a higher density than before can be formed. [Example 2] Dense Ni-Cr and porous YS
FIG. 2 shows the change in density of the mixed sprayed coating with respect to the mixing ratio when the particle size ratio of the starting powder used is changed when forming a mixed composition coating composed of Z. The experimental conditions were as follows: input = 80 kW, plasma gas flow rate = Ar: 120 l / min, H2 = 15 l / min,
Carrier gas flow rate = 15 l / min, plasma operating pressure =
200TORR, substrate position = 20cm. Type A is dense Ni-C
r from dense YSZ and Ni-Cr, Type B from dense Ni-Cr and porous YSZ, Type C from porous Ni-Cr and mixed composition coating from porous YSZ and Ni-Cr Are formed.

[0013]

The mechanical strength of the coating formed by the plasma spraying method is usually less than half that of a normal bulk material. The relationship between the sprayed coating density of YSZ and the Young's modulus is monotonically increasing, and a film having a Young's modulus of 2 to 5 times can be formed by forming a high-density coating as compared with the conventional method. FIG. 3 shows the change in Young's modulus when the mixture ratio (VOL%) of YSZ and Ni-Cr is changed. There is no example in which a mixed composition film in which all of the substances are dense is formed, and the present invention has made it possible to form a mixed sprayed film having mechanical properties close to those of a general bulk material.

According to the present invention, a film in which all components are dense can be formed, and further, density control for each component and density control of the entire film can be easily achieved. The ability to control a wide range of film quality from dense to porous is mechanical,
The control of various electrical and thermal properties is also expanding, suggesting the expansion of new application fields of plasma spraying.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between a mixture ratio and a film density when a particle size ratio is changed.

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

Continued on the front page (72) Inventor Tohru Saito 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Prefecture Nippon Steel Corporation 2nd Technical Research Institute (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C4 / 12

Claims (2)

(57) [Claims] In a method for producing a mixed composition film comprising two or more types of components by a plasma spraying method, the average particle size ratio of a starting powder is changed for each component, and the molten state is adjusted to adjust the molten state. A mixed composition plasma spraying method characterized by controlling the density. 2. The mixed composition plasma spraying method according to claim 1, wherein the average particle size ratio of each component is set such that the time (t) from room temperature to completion of melting is equal for each component.