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1. Heat treatment method
The purpose of heat treatment is to obtain an ordered structure to improve its plasticity and toughness. There are mainly the following treatment methods.
(1) High-temperature homogenization annealing The intermetallic compounds in the as-cast state generally have composition segregation and casting stress. High-temperature homogenization annealing is to eliminate the casting stress and further spread the alloy elements evenly, which lays a good foundation for the next step. The treatment generally lasts for more than ten hours at temperatures above 1000 °C.
(2) Oil quenching In order to increase the room temperature toughness of intermetallic compounds, it is often heated to a crystal transformation or phase transformation temperature, and then placed in an oil for quenching treatment, such as a typical treatment process for Fe-Al intermetallic compounds: heating To 1000 ° C, heat for 5 h, then placed in 700 ° C oil cooling for details see the reference.
(3) Deformation heat treatment This is the most effective treatment method for increasing the toughness of intermetallic compounds. It is mainly through thermal deformation treatment such as forging, rolling, extrusion, etc., which causes the structural structure to change in the direction of toughness. Typical techniques are described in the literature.
The problem of room temperature brittleness of intermetallic compounds has been a problem that has plagued the application of such materials. Alloys of the same composition may have a far different microstructure and mechanical properties due to different processing methods and process parameters. Thermomechanical treatment processes are widely used in the preparation of intermetallic compounds. A product that combines high strength and high plasticity that cannot be achieved by processing.
2. Development and application prospects
Among metal materials, intermetallic compounds have been used as a strengthening phase of a metal matrix. The purpose of controlling the performance of the matrix material is achieved by changing the type, distribution, precipitation state and relative content of the intermetallic compound. Due to its many unique properties, intermetallic compounds themselves are increasingly being researched and developed as a new class of materials. Due to its high temperature and corrosion resistance, intermetallic compounds have become important structural materials in many industrial sectors such as aerospace, aerospace, transportation, chemical, machinery, etc.; because of their special physical properties such as sound, light, electricity and magnetism, they can be used as semiconductors. Functional materials such as magnetic, hydrogen storage and superconductivity. In particular, ordered intermetallic compounds used as high-temperature structural materials have many good mechanical properties and resistance to oxidation, corrosion and high specific strength due to the long-range order of their atoms and the intermetallic bond and covalent bond between atoms. Coexistence makes it possible to combine the plasticity of metals with the high temperature strength of ceramics, which is extremely promising.
However, the brittleness of intermetallic compounds hampers its use. Until the early 1980s, two major breakthroughs were made in the study of toughening of intermetallic compounds. First, He Quanxiu of the Japan Institute of Materials Science and Technology added B with a mass fraction of 0.02% to 0.05% in brittle polycrystalline Ni3Al. The material is toughened, and the tensile elongation at room temperature is increased from nearly 0 to 40% to 50%. Second, the Oak Ridge National Laboratory found that the non-plastic hexagonal D019 structure of Co3V uses Ni and Fe to form part of Co. It can be transformed into a face-centered cubic L12 structure, and the brittle material becomes a material with good plasticity. These advances in oil-free bearings have led to the hopes and prospects of high-temperature structural materials for intermetallic compounds, setting off a research boom around the world.
At present, as an ordered intermetallic compound of high-temperature structural materials, A3B and AB-type aluminides of three systems of Ni-Al, Ti-Al and Fe-Al have been mainly studied at home and abroad.
The intermetallic compound mainly refers to a compound formed between metal elements, metal elements and metalloids, and each element has a stoichiometric composition, but the composition thereof can be changed within a certain range to form a compound-based solid solution. Intermetallic compounds have become an important branch of new structural materials due to their excellent properties between metals and ceramics, and have been widely used.