JPH0233676B2 - TANKAKEISO * KINZOKUFUKUGOKANOYOBISONOSEIZOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon carbide and metal composite pipe and a method for manufacturing the same.

Composite tubes, in which the inner surface of a metal tube is covered with ceramic, are being considered for use in combustion tubes of gas turbine engines, hot air flow transport tubes, wear-resistant cylinder liners, etc., but conventional technology in this field, namely metal over ceramic, has been considered. The joining method differs depending on the purpose, but it can be roughly divided into the following three types.

That is, the first method is a technique of casting a ceramic molded product with metal (Igurumi), but the bonding between the metal and ceramic is insufficient. The second method involves thermal spraying or vapor deposition of metal onto the surface of glass or ceramic products, or conversely, thermal spraying ceramic onto the surface of metal products, but there is a limit to the thickness of the resulting coating layer; Moreover, it often peels off during use. The third method is to coat the inner surface of a metal tube with aluminum powder and iron oxide powder using the centrifugal thermite method, and then coat the metal with the Al ₂ O ₃ layer, which is a reaction product, through the iron produced in the thermite reaction. This is a recently developed method to strengthen the bond between the two, but it is insufficient for making high-strength composite pipes.

In view of the fact that high-density silicon carbide ceramic has excellent heat resistance, thermal shock resistance, and oxidation resistance, the present invention has been developed by combining it with metal tubes to achieve dense and strong, no uneven thickness, low residual stress, and thermal shock resistance. The present invention also provides a composite pipe with high strength.

When bonding a thick, high-strength silicon carbide ceramic layer to the inside of a metal tube, the present inventor utilized a centrifugal thermite reaction to combine silicon metal present in the ceramic in a free state with iron produced by the thermite reaction. As a result of this action, the strength of the silicon carbide ceramic layer is further increased, and a strong bond is created between the metal tube and the silicon carbide ceramic layer, and the silicon carbide ceramic layer is made of Al ₂ O, which is produced as a by-product by the thermite reaction. The present invention was completed by discovering that oxidation resistance can be increased by covering with ₃ .

That is, in the present invention, a thick silicon carbide ceramic layer is formed on the inner surface of a metal tube, and an aluminum oxide layer is further formed on the surface of the ceramic layer, and the metal tube, the silicon carbide ceramic layer, and Al ₂ O The present invention relates to a silicon carbide/metal composite tube characterized in that _three layers are bonded by metal silicon, iron and/or a Si--Fe alloy present in the silicon carbide ceramic layer.

Furthermore, the present invention laminates a powder compact layer made of a homogeneous mixture of silicon carbide powder and carbon powder on the inner surface of a metal tube, and provides a layer on the surface of the powder compact layer for converting carbon in the powder compact into silicon carbide. A tubular material in which excess silicon is arranged in an annular shape relative to the required amount of silicon, and a powder layer of a mixture of aluminum and triiron tetroxide (Fe ₃ O ₄ ) is layered on the innermost layer is rotated in a centrifuge to generate sufficient centrifugal force. The present invention relates to a method for producing a silicon carbide/metal composite tube, characterized in that a thermite reaction is caused in the mixture in the innermost layer below, and silicon carbide is reactively sintered using the reaction heat.

To explain the cross section of the composite pipe of the present invention using a drawing, from the outside, 1 is a cast iron pipe used as a base material, and 2 is an iron-rich Fe-Si alloy layer that is melted by the reaction heat of the thermite reaction. This is an alloy layer formed between metallic silicon and the cast iron pipe through a layer of silicon carbide. No. 3 is a silicon carbide ceramic layer produced by infiltrating a powder compact made of silicon carbide powder and carbon powder with metallic silicon melted by the heat of thermite reaction, and reacting and sintering with the carbon in the compact. In the silicon carbide ceramic layer, some of the excess silicon exists as free metallic silicon, and the rest exists in the form of a network as a Si--Fe alloy. 4 is a continuous layer of free metallic silicon and a silicon-rich Si-Fe alloy, and the iron produced by thermite reaction forms the alloy. 5 is a layer of Al ₂ O ₃ produced by thermite reaction.

As described above, the composite tube of the present invention is obtained by utilizing the heat of thermite reaction under centrifugal force, and Si-Fe alloy is formed on the inner and outer surfaces of the silicon carbide ceramic layer by diffusion of molten silicon metal, resulting in carbonization. It is also distributed in a network shape in the silicon ceramic layer, strengthening the ceramic layer and increasing the bonding strength between the metal tube and the Al ₂ O ₃ layer. Moreover, the intervening metal layer absorbs the stress caused by the difference in thermal expansion between the layers of Al ₂ O ₃ /silicon carbide/metal tube, and no internal strain remains between them even after cooling.
Furthermore, silicon carbide ceramics are significantly oxidized in oxygen, especially in oxygen containing moisture, at temperatures above 1200°C.
However, in the composite tube of the present invention, _{the Al 2 O 3} layer on the inner surface serves to block oxygen and prevent oxidation of silicon carbide.

Due to the structure described above, the composite pipe of the present invention is dense and strong, and has little residual stress, so it has excellent thermal shock resistance, and is suitable for the various uses mentioned at the beginning of the detailed description of this specification. Furthermore, the method of the present invention has great economic effects because the reaction ends instantly and the heat of reaction can be used as is.

Examples will be explained below.

Example 1 A cast iron (FC ₃₀ ) pipe with an inner diameter of 80 mm, a pipe length of 120 mm, and a wall thickness of 4 mm was used as the outer layer metal pipe, and a commercially available α-SiC powder (GC grade, #2000 manufactured by Fujimi Abrasives Industry Co., Ltd.) was used.
#4000:#8000=7:2:1 mixture) and carbon black (Mitsubishi Chemical Industries, Ltd. Diablack)
187 g of a homogeneous mixture with a weight ratio of 1:0.8 was laminated on the inner wall of a cast iron pipe to a substantially uniform thickness (wall thickness of approximately 6 mm) so that the bulk density was 1.34 g/cm ³ . Lamination is carried out by inserting a core of an appropriate diameter into a metal tube and filling the space between the metal tube and the core with the mixture. Next, silicon powder (purity
213 g (1.1 times the theoretical amount) (99.9%, which has been blended with various particle sizes to improve filling properties) was filled to a substantially uniform thickness of about 5 mm. Furthermore, 77 g of a homogeneous mixture of aluminum powder (purity 78%, about 200 mesh) and Fe ₃ O ₄ powder (reagent grade, about 200 mesh) in a molar ratio of 8:3 was layered uniformly on the inside to a thickness of about 3 mm. The test piece prepared as described above was inserted and fixed into the center of the mold of a cantilever horizontal centrifuge used for centrifugal casting experiments.
The mold is designed not only for fixing, but also for cooling. The test piece attached to the rotating part of the centrifuge was rotated without eccentricity, and when the force reached approximately 200 G, the acetylene flame ignited the aluminum and Fe ₃ O ₄ mixture, causing a thermite reaction. The reaction sintering of silicon carbide induced by the heat generated by the thermite reaction was also an exothermic reaction, so all reactions were completed instantaneously.
After cooling, the rotation was stopped and the specimen taken out from the mold had a silicon carbide ceramic layer with a thickness of about 6 mm on the inner layer, and an Al ₂ O ₃ layer with a thickness of about 0.4 mm on the surface.
It was covered with layers.

Next, the cross section of this test piece was polished to a mirror surface, and an electron probe microanalyzer (EPMA) was used.
It was analyzed in The innermost Al ₂ O ₃ layer 5 has a thickness of about 0.4 mm, and although there seems to be some chemical bonding between the Al ₂ O ₃ layer 5 and the silicon carbide layer 3, it is mainly a Si-Fe alloy layer. 4 was involved. In the silicon carbide layer 3, about 15% of free metallic silicon containing a small amount of iron was distributed in a network shape. Between the silicon carbide ceramic layer and the cast iron pipe, there existed an iron-rich Fe--Si alloy layer 2 which was continuous with the free metallic silicon in the silicon carbide ceramic and caused diffusion bonding. Furthermore, since this reaction takes place instantaneously, no trace of the carbon combustion reaction was observed during the composition, even in air, and no air bubbles were observed.

Example 2 A heating element was placed in the composite tube prepared in Example 1, and the inner surface was heated to 1400°C and the outer surface to 600°C in air and maintained for 100 hours, but almost no change was observed.

Example 3 A test piece obtained in the same manner as in Example 1 except that the inside of the tube was replaced with argon gas was also used in Example 1.
A similar tissue cross section and test results as in Example 2 were obtained.

Example 4 The cast iron pipe of Example 1 was tested in the same manner as in Example 1 except that carbon steel with an inner diameter of 80 mm, austenitic stainless steel, and Nimonic 90 and Inconel X with an inner diameter of 30 mm were used. Impact resistance was sufficient.

Example 5 In Examples 1 and 3, when the centrifugal force was 170 to 230G, no air bubbles were observed in the test piece, but below 170G, the silicon carbide ceramic layer 3
A tendency for bubbles to remain at the interface with the Al ₂ O ₃ layer 6 was observed. Above 230G, the device will vibrate violently.
The thickness of silicon carbide layer 3 became non-uniform.

Example 6 Approximately 10 test pieces each having a pipe length of approximately 8 mm were prepared from the silicon carbide/cast iron composite pipes prepared in Example 1 and Example 3.
This was used as a test piece for individual cutting and thermal shock resistance tests. 1000℃
A rapid cooling test was repeated 20 times on the same test piece by dropping it into running water at room temperature, but no phenomenon of peeling of Al ₂ O ₃ or silicon carbide was observed. Silicon, iron, and or
It is thought that the Si-Fe alloy acts as a buffer material and alleviates the effects of thermal shock.

[Brief explanation of drawings]

The drawing shows a schematic cross-sectional view of the silicon carbide/cast iron composite pipe of the present invention. In the figure, 1...cast iron, 2...iron-rich Fe-Si
Alloy layer, 3...Silicon carbide ceramic layer, 4...Metal silicon/Si-Fe alloy continuous layer, 5... _{Al2O 3} layer.

Claims (1)

[Scope of Claims] 1 A thick silicon carbide ceramic layer is formed on the inner surface of a metal tube, and an aluminum oxide layer is further formed on the surface of the ceramic layer, and the metal tube, the silicon carbide ceramic layer, and the Al ₂ O ₃ layers present in the silicon carbide ceramic layer of metallic silicon, iron and or Si-Fe
A silicon carbide/metal composite tube, characterized in that it is bonded by an alloy. 2. A powder compact layer made of a homogeneous mixture of silicon carbide powder and carbon powder is laminated on the inner surface of a metal tube, and silicon necessary to convert carbon in the powder compact layer into silicon carbide is deposited on the surface of the powder compact layer. A tubular material in which silicon in excess of the amount of silicon is arranged in a ring shape, and a powder layer of a mixture of aluminum and triiron tetroxide (Fe ₃ O ₄ ) is layered on the innermost layer is rotated in a centrifuge under sufficient centrifugal force. A method for manufacturing a silicon carbide/metal composite tube, characterized by causing a thermite reaction in the innermost layer, and performing reactive sintering of silicon carbide using the reaction heat.