Cemented carbide as industrial teeth,which is mainly using plasticity and toughness to high hardness,high wear resistance metal compound performance and good high-temperature resistance and good bonding phase,to achieve the effect of cutting,drilling and abrasion resistance.These properties make it difficult for some of the properties of cemented carbides, such as hardness and strength, toughness and wear resistance,mainly because it is difficult to simultaneously increase the content of hard and bonded phases.Science and technology are the primary productive forces,and cemented carbidewith new structure can improve its hardness and toughness to a certain extent.The new structure mainly has gradient structure, nano and ultrafine crystal structure,ultra coarse crystal structure and other special grain distribution structure.

The cemented carbide with gradient structure refers to the gradient distribution of its hard and adhesive phases on a certain spatial scale,so that the regulation of its properties has the greatest degree of freedom.according to the performance requirements, there are many kinds of functionally graded cemented carbide.In 1980s,the development of functionally graded structures Sandvik rock drilling tools company's dual phase DP hard alloy generally show a structure similar to that of sandwich,the alloy in the outer layer and the middle layer of WC+Co phase organization,the inner WC+Co+ of three-phase microstructure. The content of Co in the outermost layer of the material is lower than the nominal cobalt content of the alloy, and has high hardness and wear resistance.The content of Co phase in the interlayer is higher than the nominal cobalt content of the alloy,and has good toughness and plasticity. The wear resistance and toughness of DP alloy are obviously better than that of standard cemented carbide.The technology is known as "the most important innovation in cemented carbide since 1950.".20 world 90s,this technology is applied to metal cutting bit, which greatly improves the life and cutting efficiency of the product.Another class of very important gradient structures cemented carbide is used for coated blade substrates.

The microstructure of cemented carbide inserts usually consists of WC,Co and beta phases. Beta phase is a brittle phase containing titanium,which can improve the hardness of the material,but reduce the toughness.There is a certain physical,chemical and mechanical incompatibility between the coating matrix and the coating.By controlling the sintering and heat treatment atmosphere, can form about 50um on the surface of cemented carbide free beta phase layer,with good toughness,and coating with high bonding strength,improve the toughness and anti collapse cutting life of blade coating greatly.The process is simple,and most cemented carbide coated blade substrates adopt this gradient structure.The research on functionally graded cemented carbide in China has been reported in 1990s,but it is still lack of systematic and deep elaboration.Because of the specialization of cemented carbide and functionally graded materials, more practical research is needed.

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