JPH11139881A - Composite sintered compact of silicon nitride and boron nitride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a composite sintered compact of the silicon nitride and the boron nitride increased in friction characteristic without lowering mechanical strength. SOLUTION: The subject compact has a two-layer structure in which a silicon nitride layer 4 containing the boron nitride (n-BN) is present on a surface of a base material 3 consisting of the silicon nitride 5, and in the silicon nitride 4 containing the boron nitride (h-BN) 6, the compd. of iron and silicon (Fi-Si) 7 is present at an intercrystalline phase between the silicon nitride 5 and the boron nitride (h-BN) 6. The content of the boron nitride (h-BN) 6 dispersed in the surface layer 4 is 3-50 vol.%. A thickness of the surface layer 4 is 30-500 μm. An average value of a longitudinal direction length of the boron nitride 6 dispersed in the surface layer 4 is 0.5-10 μm. The thickness of the compd. phase 7 of the iron and the silicon at the surface layer 4 is 0.3-10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite sintered body of silicon nitride and boron nitride suitable for sliding parts, and more particularly to a composite sintered body of silicon nitride and boron nitride utilizing the low friction property of boron nitride. is there.

[0002]

2. Description of the Related Art Since hexagonal boron nitride (h-BN) having solid lubricity has poor wettability, boron nitride (h-BN) is converted to silicon nitride (Si-BN) by firing at a low pressure of 10 atm or less. It is not possible to obtain a sintered body with a fine structure by combining with ₃ N ₄ ). On the other hand, according to high-pressure firing such as hot pressing, a dense sintered body (ceramics) in which boron nitride (h-BN) particles are dispersed in a matrix or continuous phase composed of silicon nitride (Si ₃ N ₄ ). ) Can be obtained. However, in high-pressure firing, the starting material, boron nitride (h-BN) powder, agglomerates as secondary particles during firing and the particle size increases, and many pores remain, resulting in sufficient mechanical strength. Absent. In addition, since the surface of the sintered body is uneven due to pores, the coefficient of friction increases, and boron nitride (hB
The solid lubricity of N) cannot be used. Therefore, to obtain a silicon nitride based sintered body suitable for sliding parts,
The challenge is how to combine boron nitride (h-BN), which exhibits low friction even in the boundary lubrication region, with silicon nitride, which has excellent mechanical properties.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a composite sintered body of silicon nitride and boron nitride which has improved friction characteristics without impairing mechanical strength. .

[0004]

Means for Solving the Problems In order to solve the above problems, the structure of the present invention is to provide a silicon nitride layer containing boron nitride (h-BN) on the surface of a substrate made of silicon nitride (Si ₃ N ₄ ). In a silicon nitride layer containing boron nitride, which is an existing two-layer structure, plate-like boron nitride is dispersed in the silicon nitride matrix in a direction substantially parallel to the surface of the base material, and around the boron nitride. And a compound of iron and silicon (Fe-Si).

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the composite sintered body has a two-layer structure, and boron nitride exists only in the silicon nitride layer containing hexagonal boron nitride (h-BN) as the surface layer. , The decrease in mechanical strength is small. In the silicon nitride layer containing boron nitride, which is the surface layer, the compound of iron and silicon (Fe-Si), which has a high affinity for the sintering aid, exists around the boron nitride, so it exists in the composite sintered body. The structure is dense with few pores, and there is no decrease in mechanical strength.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a composite sintered body 2 of silicon nitride and boron nitride according to the present invention is made of silicon nitride (Si ₃ N ₄ ).
A silicon nitride layer 4 (hereinafter, referred to as a surface phase) containing hexagonal crystalline boron nitride [(h-BN), hereinafter simply referred to as boron nitride] having a thickness of 30 to 500 μm ) Is a two-layer structure. As shown in FIG. 2, in the surface layer 4, a plate-like boron nitride 6 is dispersed in the matrix of the silicon nitride 5 substantially parallel to the surface of the silicon nitride 3 serving as the base material. The iron-silicon compound (Fe—Si 2) 7 is present in the grain boundary phase between. The content of boron nitride 6 dispersed in the surface layer 4 is 3 to 50 vol.%.
And the average value of the length in the longitudinal direction of the boron nitride 6 is 0.1.
5 to 10 μm. The thickness of the compound phase 7 of iron and silicon in the surface layer 4 is 0.3 to 10 μm.

[Example 1] A mixed powder of silicon (Si) powder as a main raw material, alumina (Al ₂ O ₃ ) powder and sintering aid and yttria (Y ₂ O ₃ ) powder as 80 vol. The surface of boron nitride (h-BN) powder having a particle size of 0.3 to 8 μm is mixed with 20 vol.% Of a powder coated with iron (Fe) in advance and granulated into particles having a particle size of 10 to 80 μm by a spray dryer. hand,
Particles of the thermal spraying raw material were produced.

On the other hand, silicon nitride (Si ₃ N ₄ ) as a main raw material
A compact is formed from a mixed powder obtained by adding alumina (Al ₂ O ₃ ) powder and yttria (Y ₂ O ₃ ) powder, which are sintering aids, to the powder at 10 atm and a temperature of 1300 ° C. Calcination was carried out for about 3 hours in a nitrogen atmosphere to obtain a calcined body having pores. The particles of the above-mentioned sprayed material were sprayed on the surface of the obtained calcined body. At this time, the porosity of the sprayed layer of the calcined body is set to 50 to 60%.
I made it. Next, the calcined body provided with the sprayed layer is fired in a nitrogen atmosphere at 10 atm and a temperature of 1300 ° C. for 3 hours, and then fired in a nitrogen atmosphere at 10 atm and a temperature of 1800 ° C. for 3 hours. A composite sintered body of boron nitride was obtained.

The composite sintered body 2 of silicon nitride and boron nitride according to the present invention was cut perpendicularly to the sprayed surface, and its structure was observed and analyzed with an electron microscope. The composite sintered body 2 has a two-layer structure of a silicon nitride (Si ₃ N ₄ ) layer, that is, a substrate 3, and a silicon nitride (Si ₃ N ₄ ) layer (surface layer) 4 containing boron nitride (h-BN). The porosity of both the substrate 3 and the surface layer 4 was 1% or less. In the surface layer 4, boron nitride (h-
BN) was a plate-like material parallel to the surface of the silicon nitride substrate 3 and was uniformly dispersed. This is thought to be due to the fact that boron nitride (h-BN), which was almost spherical in the raw material, was deformed by collision during thermal spraying. In addition, iron (Fe) plated on the surface of boron nitride (h-BN) changes into a compound of iron and silicon (Fe-Si) during firing, and the compound of iron and silicon has a grain boundary component. Was in close contact with No pores or cracks were found between the substrate 3 of silicon nitride (Si ₃ N ₄ ) and the surface layer 4.

After surface treatment and polishing of the composite sintered body 2 of silicon nitride and boron nitride according to the present invention, a four-point bending strength test and a sliding friction test were performed. The friction characteristics between the silicon nitride-boron nitride composite sintered body 2 of the present invention in which the content of boron nitride (h-BN) dispersed in the surface layer 4 is 17 vol. As shown in FIG. The composite sintered body 2 of silicon nitride and boron nitride of the present invention has a smaller coefficient of friction than a conventional general silicon nitride sintered body because a compound of iron and silicon (Fe-Si) is mixed in the mixed lubrication region. It is considered that the lubricating oil is adsorbed to form a lubricating oil film, and that boron nitride acts as a solid lubricant in the boundary lubrication region.

[Example 2] A plurality of composite sintered bodies of silicon nitride and boron nitride having different contents of boron nitride (h-BN) dispersed in the surface layer 4 manufactured in the same manner as in Example 1 When a four-point bending strength test and a sliding friction test were performed, the results shown in FIG. 4 were obtained. If the content of boron nitride dispersed in the surface layer 4 is 3 vol.% Or less, the effect of reducing the friction coefficient cannot be obtained, and if the content of boron nitride dispersed in the surface layer 4 exceeds 50 vol. As a result, the strength was reduced.

Example 3 The thickness t of the surface layer 4 in which boron nitride (h-BN) is dispersed, manufactured in the same manner as in Example 1,
When a four-point bending strength test and a sliding friction test were performed on a plurality of composite sintered bodies of silicon nitride and boron nitride having different (FIG. 1), results as shown in FIG. 5 were obtained. It was difficult to produce a composite sintered body of silicon nitride and boron nitride in which the thickness of the surface layer 4 was 30 μm or less. When the thickness of the surface layer 4 of the composite sintered body of silicon nitride and boron nitride exceeded 500 μm, cracks occurred in the surface layer 4 or the coating and the strength was reduced. The thickness t of the surface layer 4 depends on the thickness of the calcined body of silicon nitride serving as the base material 3 at which the particles of the thermal spraying material containing boron nitride are thermally sprayed. Occurs.

[Example 4] A plurality of composite sintered bodies of silicon nitride and boron nitride produced by the same method as in Example 1 and having different particle diameters of boron nitride (h-BN) dispersed in the surface layer 4 A four-point bending strength test and a sliding friction test were performed. As a result of the four-point bending strength test, a decrease in the strength of the composite sintered body of silicon nitride and boron nitride in which the average length in the longitudinal direction of boron nitride dispersed in the surface layer 4 is 0.5 to 10 μm is not observed. However, in the composite sintered body of silicon nitride and boron nitride in which the length of the boron nitride dispersed in the surface layer 4 in the longitudinal direction exceeds 10 μm, the particles of boron nitride serve as a starting point of fracture, and the strength is reduced.

Example 5 A plurality of silicon nitride and boron nitride were formed in the same manner as in Example 1 by using a material having a different iron (Fe) plating thickness on the surface of boron nitride (h-BN) as a starting material. By dispersing iron in the surface layer 4 of the composite sintered body 2 of silicon nitride and boron nitride by changing the thickness of iron plated on the surface of boron nitride (h-BN). The effect of the thickness of the iron and silicon compound (Fe-Si) phase was tested. As a result of the test, when the thickness of the compound phase of iron and silicon present in the surface layer 4 of the composite sintered body 2 of silicon nitride and boron nitride is 0.3 μm or less, a portion where iron is not plated on the surface of boron nitride , Pores are formed in the iron-silicon compound phase. When the thickness of the iron-silicon compound phase present in the surface layer 4 of the composite sintered body 2 of silicon nitride and boron nitride exceeds 10 μm, the iron-silicon compound phase is formed inside the iron-silicon compound phase. There was a part of the iron that did not remain, and cracks occurred in this part, and the strength was reduced.

[0015]

As described above, the composite sintered body of silicon nitride and boron nitride of the present invention has a nitride containing boron nitride (h-BN) on the surface of a substrate made of silicon nitride (Si ₃ N ₄ ). In a two-layer structure in which a silicon layer is present, in a silicon nitride layer containing boron nitride, that is, a surface layer, a compound of iron and silicon (Fe-Si) is present in a grain boundary phase between boron nitride and silicon nitride. In particular, in the surface layer, there is a compound of iron and silicon, which has a high affinity for the sintering aid, around the boron nitride, so that during the sintering, the boron nitride particles aggregate and agglomerate. Is suppressed. For the reasons described above, the low friction property of the boron nitride in the surface layer is exhibited without impairing the mechanical strength of the silicon nitride as the base material.

Accordingly, when the composite sintered body of silicon nitride and boron nitride of the present invention is used for a sliding part such as a cylinder liner or a bearing of an internal combustion engine, power loss due to friction is reduced and fuel consumption can be reduced. .

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an outline of a composite sintered body of silicon nitride and boron nitride according to the present invention.

FIG. 2 is a side sectional view schematically showing the structure of a composite sintered body of silicon nitride and boron nitride.

FIG. 3 is a strike diagram showing friction characteristics of the composite sintered body of silicon nitride and boron nitride.

FIG. 4 is a diagram showing the relationship between the four-point bending strength and the friction coefficient with respect to the content of boron nitride in the surface layer in the composite sintered body of silicon nitride and boron nitride.

FIG. 5 is a diagram showing the relationship between the four-point bending strength and the friction coefficient with respect to the thickness of the surface layer in the composite sintered body of silicon nitride and boron nitride.

[Explanation of symbols]

2: Composite sintered body 3: Base material (silicon nitride layer) 4: Silicon nitride layer containing boron nitride 5: Silicon nitride 6: Boron nitride 7: Compound of iron and silicon

Claims (4)

[Claims] 1. A silicon nitride layer containing boron nitride (h-BN) is present on the surface of a substrate made of silicon nitride (Si ₃ N ₄ ).
In a silicon nitride layer containing boron nitride, which is a layer structure,
In the silicon nitride matrix, plate-like boron nitride is distributed almost uniformly and parallel to the substrate surface, and a compound of iron and silicon (Fe-Si) exists around the boron nitride. A composite sintered body of silicon nitride and boron nitride. 2. The silicon nitride layer containing boron nitride (h-BN) has an average longitudinal length of boron nitride particles of 0.5 to 10 μm, and a boron nitride content of 3 to 10 μm.
The composite sintered body of silicon nitride and boron nitride according to claim 1, which is 50 vol.%. 3. The silicon nitride according to claim 1, wherein the thickness of the compound of iron and silicon (Fe-Si) in the silicon nitride layer containing boron nitride (h-BN) is 0.3 to 10 μm. And boron nitride composite sintered body. 4. The composite sintered body of silicon nitride and boron nitride according to claim 1, wherein said silicon nitride layer containing boron nitride (h-BN) has a thickness of 30 to 500 μm.