JPS61169241A - Heat-insulating member - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a heat insulating member, in particular a ceramic sprayed layer provided on the surface of the member to improve the heat insulating properties of a member exposed to high temperatures such as engine parts of an automobile. It relates to a heat insulating member. Since the combustion gas temperature of an engine is high, and the higher the combustion gas temperature, the better the thermal efficiency, so in order to improve the heat resistance of the engine and related parts, a ceramic layer is formed on the surface of those parts. Research is underway to make all the parts out of ceramic.

Conventional technology and problems to be solved by the invention Conventionally, when spraying ceramics such as zirconia, anomina, chromia, etc. on the surface of base materials such as iron or aluminum for engine parts and other parts, an undercoat of nickel-based alloy is used. A method of forming a ceramic layer through a material has been frequently used. However, when a test piece sprayed by this method is subjected to a thermal cycle test, cracks occur within the ceramic layer or near the boundary between the ceramic layer and the undercoat layer, which eventually leads to peeling. This crack is thought to be caused by the difference in thermal expansion between the base material and the ceramic layer or by the thermal stress of erosion.

Furthermore, in order to extend the durability until cracking occurs, it has been conventionally done to increase the porosity. (Literature: RANGASW meter Y & Il, llEIIM8N
, TI to EIIM 81° EXP to NSION 5Tt
lrlY 011 PLASMA-3Pl'lA'
/El'10XIDECOATINGS, Th1n 5
(Olid Film, 73 (1980) 43-52, etc.) However, in this case, the shape of the pores is not controlled, so there are many pores that extend parallel to the direction t of crack propagation. The ceramic layer appears to be easily cut, and the durability is not sufficient.

The second problem is even more serious because sliding members such as pistons are exposed to severe mechanical conditions in addition to thermal conditions.

Means for Solving the Problems In order to solve the problem of double porosity, the present invention makes the pores of the ceramic layer formed on the surface of the base material of the heat insulating member spherical.

By making the pores spherical, the occurrence and propagation of cracks is suppressed compared to the conventional case where the pores are irregularly shaped.

In order to make the pore shape of the ceramic layer into a spherical shape, it is necessary to coat it with a 1-gun nostle. "1 separation (1 or less,
The spray conditions such as the spraying distance (hereinafter referred to as the spraying distance), the current value during thermal spraying, the particle size of the spraying powder (hereinafter referred to as the powder particle size), the shape of the spraying powder (hereinafter referred to as the powder shape), and the amount of powder supplied are appropriately adjusted. You can select . Generally speaking, this is achieved by injecting nearly spherical particles of uniform size under conditions that cause them to partially melt. In addition, H after thermal spraying
IP processing (Ilot l5o-static Pre
Partial melting of the particles is also possible by performing ssinB), and the shape of the pores can also be made spherical.

In a preferred embodiment of the present invention, as shown in FIG. 1, after undercoat 1-b is thermally sprayed onto a base material a such as a 1N moving part, a ceramic layer C having a small porosity is first provided, and then a ceramic layer C having a spherical pore shape is provided. A -12 ceramic layer d with a high porosity is provided, and finally a ceramic layer e with a small porosity is provided as the outermost surface layer.

The ceramic layer C having a low porosity immediately above the undercoat layer acts to improve the adhesion between the undercoat 1-b and the ceramic layer. The ceramic layer d, which is spherical and has a high porosity, acts to alleviate stress caused by the difference in thermal expansion of the base ceramic material during thermal cycling, making it difficult for the ceramic layer to crack or peel. Even when η- occurs, due to its spherical shape, the propagation speed of cracks is slow, making it difficult to cause peeling. It also acts to prevent corrosive gases from entering the sprayed layer from the outside and erosion when forming a ceramic layer with a low porosity near the surface, a thermal cycle, etc. Regarding the three-layer structure in which a ceramic layer with a high porosity is sandwiched between a ceramic layer with a low porosity, please refer to our earlier application (Japanese Patent Application No. IJ-53F171, 1973).
.

Examples In the following examples, after forming an undercoat layer on the base material a as shown in Fig. 1, by changing the thermal spraying conditions from the standard conditions, etc., a ceramic thermal spraying layer with a low porosity was applied. A three-layer structure is formed consisting of a layer C, a layer d with spherical pores and a high porosity, and a layer e with a low porosity.

Steel material (+15 standard SO5304) diameter 8II11,
A cylindrical test piece a having a length of 50 fins was prepared. An undercoat layer was formed on this test piece by thermally spraying a Ni-Cr-Al alloy to a thickness of 0.11 mm using a plasma melting gun.

Next, zirconia stabilized with 5wt''l of calcium oxide was injected to form a ceramic layer having the above three-layer structure.In forming each layer of the three-layer structure, the following conditions were met. Adopted.

■ The layer with low porosity near the interface I1 of the undercoat layer (layer C in Figure 1) is sprayed at a spraying distance of 9 using a plasma spray gun.
Under thermal spraying conditions of 0 m++, current value of 600 A, and powder particle size of -350 mesh, the ceramic layer was melted to a thickness of 0.1 mm to form a ceramic layer with a porosity of 3 to 8%.

■ A layer with high porosity and spherical pores (layer d in Figure 1) formed in the negative part of the C layer is sprayed using a plasma spray gun at a spraying distance of 140 parts, a current value of 350 to 400 A, and a) end. The ceramic layer is thermally sprayed to a thickness of 0.21 mm using spheroidized powder with a particle size of 350 to 500 mesh, and has a porosity of 12 to 20% with a porosity of about φ10 to 20μ. was formed. It was confirmed by microscopic observation that the pores were spherical.

(2) A layer with low porosity (layer 0 in FIG. 1) formed on top of layer d was prepared using the same method, thickness, and porosity as the layer 0.

However, it is not necessary that the 0 layer is the same as the 0 layer; it is desirable to determine the porosity of the 0 layer according to the intended use.

1! In the example of 1-, the above thermal spraying conditions were used, but if the porosity becomes desired, other conditions may be used. It goes without saying that the ceramic layer may be formed by thermal spraying 81 under certain conditions (for example, the spraying angle, the temperature of the sprayed surface, etc.), or it may be thermally sprayed by combining many thermal spraying conditions. Regarding the thermal spraying method, plasma spraying is considered to be the best method in terms of adhesion, but other gas spraying or arc type spraying may also be used.

In addition, as a method for spheroidizing the pores, T(I
P treatment etc. can also be mentioned.

Using the ceramic melt 1]=j test piece prepared in the above example, a cooling/heating cycle test was conducted in which cycles were repeated between a high temperature of 900° C. and room temperature. As a result, it took 700 heating and cooling cycles before a certain type 11 was observed on the ceramic sprayed layer.

For comparison, a test piece ( Comparative Example A) was also subjected to the same thermal cycle test. In addition, although the rest is the same as the example, the pore shape of the intermediate ceramic layer d is not spherical (
The same thermal test was also conducted for Comparative Example B). (Layer d has a spraying distance of 128mm, a current value of 420A, and a powder particle size of 350~
Created under thermal spraying conditions of zirconia particles of 500 mesos.
Microscopic observation revealed that the pores were not uniform in shape and were often angular and flat. ) These results are summarized in Figure 2. From FIG. 2, it can be seen that the example of the present invention, that is, the one with a spherical pore shape, has a higher resistance to cooling and heating cycles than the one with a non-spherical pore shape (Comparative Example B) under the same conditions. The durability has increased by 1.5 times, and especially compared to the conventional product (Comparative Example A) where the pore shape is not spherical and does not have a three-layer structure, the durability has increased by 23 times. shown.

Effects of the Invention The present invention provides a heat insulating member with excellent thermal properties and durability by making the pores of the heat insulating surface ceramic coat layer spherical, and by combining this with porosity control. It can be used as sliding members and other heat-insulating mechanical parts.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a heat insulating section H having a ceramic sprayed layer according to the present invention, and FIG. 2 is a graph showing the results of a thermal cycle test. a...Base material, b...Undercoat layer, C...Ceramic layer with low porosity, d...Ceramic layer with high porosity and spherical pores, e...Ceramic layer with high porosity . Song 1 Figure 2 - Mi 2] Comparative Example A Comparative Example B Example Procedures Amendment (Method) May 2, 1985

Claims (1)

[Claims] 1. After applying an undercoat on the base material of the heat insulating member, a ceramic layer with a low porosity, a ceramic layer with a high porosity, and a ceramic layer with a low porosity are formed in order from the inside. A heat insulating member characterized by a ceramic layer having a spherical pore shape.