Effects Of Adding Transition Metal Compounds On Microstructure And Properties Of Silicon Nitride Ceramic Balls

With the development of science and technology in recent years,people have put forward higher requirements for the performance of silicon nitride ceramic materials.Silicon nitride ceramic ball is a kind of high-precision parts,and it is widely used in the bearings of precision machine tools,high-power wind power generation bearings and aerospace bearings.However,at present,silicon nitride ceramics still have fatigue cracking,creep cracking and other failures because the mechanical properties cannot meet the requirements of their working conditions.How to improve its mechanical properties under the existing conditions so that it can meet the use conditions of special working conditions has become the focus of the industry.This paper takes silicon nitride ceramic balls as the research object and focuses on the effects of adding three transition metal compounds,TiN,Fe3Si and WC,on the microstructure,interface structure and mechanical properties,and explores the relevant mechanisms,and draws some conclusions.（1）TiN can refine the grains under the condition of ensuring the uniform structure of silicon nitride;adding Fe₃Si will generate a specific sintered structure in which some coarse grains are interpenetrated and bridged,and the gaps are filled with fineβ-Si₃N₄grains;WC cannot guarantee the uniformity of the structure and coarse and fine crystals coexist.（2）Adding TiN can effectively inhibit the formation of the second phase Si₂N₂O in the sintering process;adding TiN and WC is conducive to the diffusion of Al and O into the silicon nitride matrix during the sintering process,increasing the unit cell parameters and forming a Sialon phase with better performance.Adding Fe3Si does not have this effect.（3）After adding TiN,two types of dense grain boundaries were observed in the silicon nitride structure,one with a small angle grain boundary structure of[1-213]/12°,and the other with a dense general large angle grain boundary.No similar grain boundaries were observed after adding Fe₃Si and WC.（4）Compared with Fe₃Si and WC,TiN-added silicon nitride ceramic balls have better mechanical properties,such as higher hardness and larger elastic modulus,thanks to its fine and uniform structure and the contribution of Sialon phase.And there is no precipitation of harmful phase Si₂N₂O.（5）Ceramic balls added with excessive WC will fail before reaching the service life.This is because the elastic modulus and hardness will be further improved after excessive addition of WC,but the toughness will be lost;the elastic modulus,hardness and toughness of ceramic balls with a small amount of TiN can be improved good keep.