Wed, 24 Oct 2018 03:04:11 +0000
Heat treatment of metal compound materials
Intermetallic compounds mainly refer to the compounds formed between metal elements, metal elements and metalloids. There are stoichiometric components among the elements, but their composition can change within a certain range to form solid solution based on compounds. Intermetallic compounds have become an important branch of new structural materials because of their excellent properties between metals and ceramics, and have been widely used.
Heat treatment mode
The aim of heat treatment is to obtain some ordered structure to improve its plasticity and toughness. There are mainly several ways to deal with them.
(1) Compositional segregation and casting stress generally exist in as-cast intermetallics after high temperature homogenization annealing. High temperature homogenization annealing is to eliminate casting stress and make alloy elements further diffuse evenly, laying a good foundation for the next treatment. This treatment usually lasts more than ten hours above 1000 C.
(2) In order to increase the toughness of intermetallic compounds at room temperature, oil quenching is often heated to the temperature of crystalline transformation or phase transformation, and then quenched in oil. For example, the typical treatment process of Fe-Al intermetallic compounds is heating to 1000 C, holding for 5 h, and then cooling in 700 C oil.
(3) Thermo-mechanical treatment is the most effective way to increase the toughness of Intermetallics at present, mainly through forging, rolling, extrusion and other thermal deformation treatment, so that the microstructure of the intermetallics will change in the direction of increasing toughness. Typical processes are listed in the literature.
The brittleness of intermetallic compounds at room temperature has been a problem that puzzles the application of such materials. The microstructure and mechanical properties of alloys with the same composition may differ greatly due to different processing methods and process parameters. Thermomechanical treatment is widely used in the preparation of intermetallic compounds. This method can obtain a good match between high strength and high plasticity which can not be achieved by general processing. Combined products.
Development and application prospects
In metallic materials, intermetallic compounds have been used as reinforcing phases of metallic substrates. The properties of matrix materials are controlled by changing the types, distribution, precipitation state and relative content of intermetallic compounds. Intermetallic compounds, as a new kind of materials, are being studied and developed more and more widely due to their unique properties. Intermetallic compounds have become important structural materials in many industrial sectors, such as aviation, aerospace, transportation, chemical industry, machinery and so on, because of their high temperature resistance and corrosion resistance. Ordered intermetallic compounds, especially those used as high-temperature structural materials, have many good mechanical properties, oxidation resistance, corrosion resistance and high specific strength. Because of the long-range ordered arrangement of atoms and the coexistence of interatomic metal bonds and covalent bonds, it is possible to have both the plasticity of metals and the high-temperature strength of ceramics. It has great application prospects.
However, the brittleness of intermetallic compounds hinders its application. Until the early 1980s, there were two breakthroughs in the toughening of intermetallic compounds. One was that the Japanese Institute of Materials Science and Koizumi et al. added 0.02%-0.05% B into brittle polycrystalline Ni3Al to toughen the material, and the tensile elongation at room temperature increased from nearly 0 to 40%-50%; the other was that the Oak Ridge Country of the United States had a solid state. The laboratory found that in Co3V with non-plastic hexagonal D019 structure, using Ni and Fe to replace part of Co can transform it into L12 structure of FCC and brittle materials into materials with good plasticity. These developments make people see the hope and Prospect of high temperature structural materials of intermetallic compounds, and set off a research upsurge worldwide.
At present, the ordered intermetallic compounds, as high temperature structural materials, have been studied and made great progress both at home and abroad, mainly in the three systems of Ni-Al, Ti-Al and Fe-Al, A3B and AB type aluminides.
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