JPS6247469A - Heat insulating member - Google Patents

Abstract

PURPOSE:To improve the durability of a heat insulating member obtd. by forming a ceramic layer on a base material with an undercoat in-between, by forming a buffer layer on the boundary between the base material and the undercost so as to improve the adhesion of the ceramic layer to the base material. CONSTITUTION:An undercoat (b) is formed on the roughened surface of a base material (a) by thermal spraying and a ceramic layer (c) is formed on the undercoat (b) by thermal spraying. At this time, a buffer layer (p) having pores is formed in the base material (a) and near the boundary between the base material (a) and the undercoat (b) or a buffer layer (q) having voids (s) is formed on the boundary between the base material (a) and the undercoat (b). The buffer layer absorbs large thermal expansion of the base material (a) and relieves thermal stress produced by the difference in thermal expansion between the base material (a) and the ceramic layer (c), so the adhesion of the ceramic layer (c) to the base material (a) can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to heat insulating members, and in particular, to improve the heat insulating properties of members exposed to high temperatures, such as engine parts of automobiles, the present invention is directed to heat insulating members. This invention relates to an improvement in a heat insulating member on which a ceramic layer is formed by thermal spraying.

[Conventional Technique 1] Conventionally, when forming a ceramic layer by thermal spraying, a base material is undercoated with a Ni-based alloy in advance.

This is because the coefficient of thermal expansion of the base material, such as Aβ, is higher than that of ceramic, and since ceramics inherently have poor adhesion to metals, the undercoat absorbs the difference in thermal expansion and improves the adhesion. It is designed to improve.

However, when test specimens of heat insulating materials and combustion and exhaust system parts manufactured using this method were subjected to thermal cycles, it was found that There was a problem that cracks formed in the parts. Also, this allows
As a result, there was a problem in that the sprayed layer peeled off.

The causes of such problems are the difference in thermal expansion between the base material and the sprayed layer, and cracking caused by erosion thermal stress.

In order to prevent this peeling, conventionally known literature RAN
GASWAMY&H,HERMAN,THERMAL
EXPANSION 5TADYOF PLAS
MASPRA'1. D 0XIDE C0ATIN
GS, Th1n SoIlidFifm, 73 (1
980) 43-52, attempts have been made to alleviate the difference in thermal expansion by increasing the porosity of the sprayed layer.

[Problem that the invention seeks to solve]

However, in this case, there was a problem in that the adhesion between the ceramic layer and the undercoat decreased, and there was also a problem in that durability was insufficient due to the difference in thermal expansion between the undercoat and the base material.

Furthermore, methods of increasing the roughness of the base material surface by increasing the size of the shot blast particles in the shot blasting method, or by sharpening, etc., and improving adhesion through the anchoring effect have also been considered, but in this case as well, the There was a problem in that sufficient durability could not be ensured due to the large coefficient of thermal expansion.

The above problems are even more serious in sliding parts such as pistons, which are exposed to severe mechanical conditions in addition to thermal conditions.

Therefore, an object of the present invention is to improve the adhesion between the undercoat and the base material, thereby improving the durability of the heat insulating member.

[Means for solving problems]

Therefore, the heat insulating member according to the present invention is characterized in that a buffer layer is provided between the sprayed layer and the base material to absorb the difference in thermal expansion between them.

Specifically, in a heat insulating member in which an undercoat is applied on a base material of the heat insulating member and a ceramic layer is formed on the undercoat, a buffer layer is provided at the boundary between the base material and the undercoat to absorb the difference in thermal expansion. It was formed.

In a preferred embodiment of the present invention, the ceramic layer C is sprayed after the undercoat b is sprayed onto the base material a whose surface has been textured in advance. Then, as shown in FIG. 1, a buffer layer p having pores is provided in the base material a near the boundary between the base material a and the undercoat b, or as shown in FIG. A buffer Mq is provided.

[Effect]

To explain in detail the present invention having the above configuration, the buffer layer absorbs the large thermal expansion of the base material and relieves thermal stress caused by the difference in thermal expansion between the base material and the sprayed layer. It works to improve adhesion.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

(Product of the present invention) Using the heat insulating member of the example shown below, a fin with a diameter of 8 and a length of 5
A 0 mm cylindrical test piece was prepared.

(First Example) FIG. 1 is a sectional view showing a first example of a heat insulating member according to the present invention.

First, when casting A1 base material (JIS ACBA equivalent) a, by adjusting the solidification rate of the A1 surface,
A blowhole is formed just below the surface. Next, this is subjected to shot blasting or surface roughening.

As an undercoat b, 9.1 m of 75Ni-19Cr-6A# alloy was applied to the surface of the base material a thus obtained.
It was formed by plasma spraying to a thickness of m.

Then, on top of this, ZrO is added as a ceramic layer C.
It was formed by plasma spraying 2.5CaO to a thickness of 0.5H. In this way, a heat insulating member 2 having a layered structure as shown in FIG. 1 was obtained.

To explain the operation of the first embodiment according to the above structure, the buffer layer p formed at the boundary between the base material a and the undercoat b
However, the voids in the layer absorb the thermal expansion of base material a, relieve the shear stress at the interface caused by the difference in thermal expansion with undercoat b, and improve the adhesion between base material a and undercoat B. It acts to improve.

(Second Embodiment) FIG. 2 is a sectional view showing a second embodiment of the heat insulating member according to the present invention.

First, AI! As shown in Fig. 3, a cross-section was prepared on the surface of the base material a with a groove depth H of 0.5 m, a groove pitch T of 0.4 m, and an angle θ at the top of the grooves of 300. A continuous isosceles triangular groove 32 is formed.

Next, an undercoat b and a ceramic layer C are applied to the surface of the base material a thus obtained in the same manner as in the first embodiment.
was formed.

In this way, a heat insulating member 3 having a layered structure as shown in FIG. 2 was obtained.

The heat insulating member thus obtained has a sawtooth surface on the base material a, as shown in FIG.
Since the top of groove 2 had an acute angle, undercoat b could not penetrate to the deepest part of groove 32, leaving a gap S.

To explain the operation of the second embodiment according to the above configuration, when the base material a thermally expands, the buffer Jlq having the void S formed in the base material a and near the boundary with the undercoat b It deforms elastically or plastically, relieves the shear stress at the interface caused by the difference in thermal expansion with the undercoat b, and acts to improve the adhesion between the base material a and the undercoat b.

In order to evaluate the performance of the heat insulating member produced in the above examples, a cold/heat cycle test was conducted in which the heat insulating member was repeatedly tested at a high temperature of 400° C. and at room temperature.

(Comparative product) For comparison, a heat insulating material was used that had the same composition as the example of the present invention and did not form a blowhole directly under the surface, and was formed using the same thermal spraying material and the same thermal spray layer thickness as the example. A cylindrical test piece similar to the product of the present invention was created using the member.

As a result of this test, the thermal sprayed layer of the comparative product peeled off after 50 to 100 cycles of heating and cooling, but the thermal sprayed layer of the product of the present invention showed no cracks or peeling even after 2000 cycles.

In addition, as shown in FIG. 4, the heat insulating members 44 of the products of the present invention and comparative products were attached to a piston body 41 made of aluminum alloy (equivalent to JISACBA) and having a nozzle hole 42 with an outer diameter of 83 mm.
A piston 4 formed on the inner surface of the nozzle hole was created, and the piston 4 was installed in each different engine and subjected to an evaluation of an actual machine subjected to a cooling/heating cycle.

The conditions for the actual machine evaluation were an engine speed of 4500 rpm and a compression ratio of 18.

As a result, peeling and falling off of the sprayed layer occurred in almost all of the comparative pistons subjected to the evaluation after 5 to 10 hours, but no abnormalities were observed in the pistons of the present invention even after 500 hours.

Although the present invention has been described above based on specific embodiments, it is not limited thereto, and various other embodiments can be considered by those skilled in the art within the scope of the claims. For example, plasma spraying is considered to be the best thermal spraying method in terms of adhesion, but other gas spraying or arc spraying may also be used.

〔Effect of the invention〕

As explained above, the present invention provides a heat insulating member in which an undercoat is applied on a base material of the heat insulating member and then a ceramic layer is formed thereon, in which a difference in thermal expansion is created at the boundary between the base material and the undercoat. Since the absorbing buffer layer is formed, the adhesion between the sprayed layer and the base material can be improved, and the durability of the heat insulating member can be improved.

In addition, especially when the outer periphery of the base material is cooled or the expansion is suppressed by a bore etc., such as a piston, which receives relative compressive stress from the outside, thermal spraying due to thermal expansion of the base material This has the excellent effect of reducing the influence on layer interfaces.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the first embodiment of the heat insulating member according to the present invention, FIG. 2 is the same (a sectional view showing the second embodiment), and FIG. FIG. 4 is a cross-sectional view showing an enlarged boundary portion, and FIG. 4 is a cross-sectional view showing a state in which the heat insulating member according to the present invention is incorporated into the nozzle hole portion of the piston. 2.3 - Heat insulating member a --- --- Base material b ---------- Andal coat c --- Ceramic layer p, q --- Buffer layer Applicant: Toyota Motor Corporation Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In a heat insulating member in which an undercoat is applied on a base material of the heat insulating member and a ceramic layer is formed on the undercoat, a buffer layer is formed at the boundary between the base material and the undercoat to absorb a difference in thermal expansion. A heat insulating member characterized by: