JPS61210137A - Manufacture of silicon nitride fiber frinforced metal - Google Patents

Abstract

PURPOSE:To facilitate the wetting of silicon nitride fibers with molten metal and to fill easily the metal into the voids among the fibers by covering the fibers with metallic powder having a prescribed particle size and reacting readily with Si and by heating the covered fibers to metallize the surfaces of the fibers. CONSTITUTION:Silicon nitride fibers are immersed in a suspension contg. metallic powder having a diameter <=1/10 time the diameter of the fibers and reacting readily with Si, and the fibers are pulled up and dried. The silicon nitride fibers covered with the metallic powder is heated at a high temp. in vacuum to metallize the surfaces of the fibers. Molten metal is filled into the voids among the metallized fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a metal matrix composite material using silicon nitride fibers as a reinforcing material.

[Technical background of the invention and its problems]

Silicon nitride has low specific gravity, high strength, and high elastic modulus, so it is expected to be applied to various structural members. Bulk materials can be processed into parts as they are and used, but fibrous materials are being considered to be embedded in plastic or metal and used as composite materials. When used as a composite material, in order to make the most of the properties of silicon nitride, it is desirable to use it in combination with metals, especially metals. Generally, the following methods are known as methods for forming metal matrix composite materials.

(1) Metal f dissolved into bundled or matted fibers
e Liquid metal impregnation method. (2) A powder metallurgy method in which fibers and metal powder are mixed and sintered after pressing. (3) A layered method in which the fibers are formed while being electroplated. (4) A vapor deposition method in which metal is attached to fibers by vacuum vapor deposition or chemical vapor deposition and then hot pressed. (5) A diffusion method in which fibers are sandwiched between metal foils and hot pressed.

However, in the method (1) above, the molten metal 1-
If the fibers are made of a material that is difficult to wet with metal during immersion, it will be difficult to impregnate the fiber bundle with molten metal. (2
) When using the powder metallurgy method, the fibers often break when the fibers and metal powder are mixed and pressed.

The brazing method (3) is limited to long fibers made of a good electrical conductor such as metal, and furthermore requires a considerable amount of time, making it industrially unsuitable. The evaporation method (4) is also difficult to produce and costs 2°C considerably.

Due to the diffusion method, laminating the Cμ fiber and metal foil is extremely difficult. These problems make it difficult to mold the entire area reinforced with silicon nitride fibers.

[Purpose of the invention]

The object of the present invention has been made in view of the above points, and the object of the present invention is to produce silicon nitride fibers using metallization on the surface of silicon nitride fibers, to which the molten metal impregnation method can be applied to obtain the most compact molded products as a composite material. A method of manufacturing a reinforced metal is provided.

[Summary of the invention]

The present inventors have made various attempts to produce silicon nitride fiber-reinforced metal by a molten metal impregnation method, and have found that it is essential to coat the fiber surface with a substance that is easily wetted with molten metal. However, in conventional coating methods for silicon nitride, such as chemical vapor deposition, physical vapor deposition, and electroless plating, the coating layer is physically attached to the surface and is easily peeled off when impregnated with molten metal. Therefore, we conducted research into a method for forming a chemically strongly bonded coating layer, and found a new metallization method, resulting in the present invention.

That is, the present inventors discovered that silicon nitride was heated in a vacuum at a high temperature.
We focused on the fact that the surface slightly decomposes into its constituent elements, and after repeated experiments, we discovered the conditions under which the decomposed elements easily react with certain metals and become molten, and we discovered that this is an effective metallizing method. I found out that it can be used as

The certain metals mentioned here are those that easily react with silicon, and the alloy formed by the reaction is lower than the melting point of the original metal, and the temperature at which the surface of silicon nitride decomposes an effective amount of silicon for the reaction ( 1,200 under a vacuum of 10-'Torr
metals that do not melt at temperatures (about ℃), such as Fe, Ni
, Co and alloys containing at least 50% of these metals such as silicon steel, carbon steel 1 alloy steel, special steel, N
There are i-0r alloy, N1-AA gold alloy, Ni-Tl alloy, various superalloys, etc.

The reaction occurs through the following process.

1. Decomposition of the surface of silicon nitride 2. Reaction between metal placed on the surface of silicon nitride and silicon 3.
Lowering of the melting point of the metal due to the reaction between the metal and silicon 4 Melting of the metal 5 Wetting of the molten metal with silicon nitride 6 Completion of metallization Therefore, in order to produce metallization, the surface of the silicon nitride must partially decompose. to give conditions to do so.

Presence of a decomposing surface 1. It is important that the metal to be reacted be in close contact with the decomposing surface. For this purpose, heating silicon nitride to a high temperature in a vacuum is effective for decomposition.
An excellent method is to use metal powder as a means of simultaneously satisfying the presence of a decomposed surface and the adhesion of metal. This is also the point of the present invention.

The thickness of the metallized layer formed by this method varies depending on the particle size and amount of powder initially placed on the silicon nitride surface. In the case of fibers with a diameter of several micrometers or less, such as whiskers, when the metallized layer becomes several micrometers, the substance of the fiber disappears. Therefore, in order for the fiber to function effectively, it must be metalized so that about 80% of the cross-sectional area remains, so the diameter of the metal powder attached to the surface of the silicon nitride fiber should be 1710 or less than that of the fiber. There is a need.

As a method for disposing metal powder on the surface of a fibrous substance, there is a method in which the metal powder is suspended in a liquid and the fibers are immersed therein. The amount of metal powder adhering to the fiber surface can be controlled by the amount of powder in the liquid.

[Embodiments of the invention]

Example A silicon nitride whisker Lop with an average length of 50 μm and an average diameter of 5 μm was added to 200 CC of water with Ni having an average particle size of 300 μm.
After immersing the fine powder in 0.5f@turbid solution and stirring thoroughly, Cl1i was added using the whisker T-filter.
Start out. Fine Ni powder is attached to the surface of the whisker. After drying the whiskers, place them in a vacuum oven and heat them 2X.
Evacuate to 10 Tart vacuum, and in that state, 1230
Increase temperature to ℃. After holding for 10 minutes, it was cooled.

The surface of the whisker taken out from the furnace was metallized with an Nl-Si alloy. Although its thickness is extremely thin, it is impossible to measure it accurately, but it appears to be xooooX or less, based on a scanning electron microscope.

The whiskers were bundled and inserted into a graphite crucible with an inner diameter of 10 da, and melted at 700°C in a vacuum.
1 alloy was injected into 1. The wettability between the metallized snow on the surface of the whisker and the alloy is extremely good.
The whiskers were completely impregnated by capillary action. After cooling, seven silicon nitride whiskers were taken out from the crucible, a part of the alloy composite material was cut out, and when it was observed under a microscope, it showed a dense structure with no pores. Silicon nitride whisker content is 30vol! X, the mechanical properties have a Yang Yi rate of 13,
500#/J, tensile strength is 55/- after T6 heat treatment
There was.

Note that the method of the present invention is not limited to the above embodiments, and the molten alloy is not limited to aluminum, but may be Fe-based or Ni-based.

Cu-based, Mf-based, etc. are effective. Further, the melt impregnation step may be carried out continuously in the same vacuum furnace immediately after metallization, and the atmosphere during the melt impregnation may be either reducing or inert.

〔Effect of the invention〕

By using the method of the present invention, silicon nitride fiber metal can be easily and reliably produced.

Agent: Patent Attorney Noriyuki Chika (1 other person)

Claims (1)

[Claims] A step of immersing a silicon nitride fiber in a liquid in which a metal powder that easily reacts with Si having a diameter of 1/10 or less of the fiber is suspended, a step of lifting the fiber from the liquid and drying it, and a step of drying the fiber. 1. A method for producing a silicon nitride fiber-reinforced metal, comprising the steps of metallizing the surface of the fibers by heating in a high-temperature vacuum, and impregnating the metalized fiber bundle with molten metal.