Preparation And Sintering Properties Of Coated TiB₂-YAG Composite

TiB2 exhibits high electrical conductivity, melting temperature and wear resistance, low specific weight and relatively good chemical stability, besides its extremely high hardness and elastic modulus. TiB2 ceramics are very promising in modern industry. The main problems that limit the application of TiB2 ceramics include:high fabrication cost, low sintering activity and the inherent brittleness. Adding second ceramic phase, using sintering aids and optimizing fabrication technologies are believed important ways to improve its mechanical properties, sinterability of ceramics and cut down on costing.In this paper, the train of thought that resolving sintering densifiction was proposed YAG powders were coated on the surface of TiB2 particles to form TiB2-YAG composite powders with coating structure and easy sintering densification,TiB2-YAG ceramics with coating structure were prepared through hot pressed sintering(HP).First, The precipitate with the microstrue ture of Y(OH)3coating Al(OH)3was obtained through keeping constant pH value in the co-precipitation proeessing, and pure YAG phase can be prepared after calcination precipite at 900℃. Nanoscaled YAG powder with the size of 20-30nm can be prepared by the co-precipitation method. Second, Y(OH)3+A1(OH)3 composite particles were synthesized by the chemical precipitation method.The dispersibility of TiB2 particles and the conditions of synthesizing Y(OH)3+Al(OH)3/TiB2 composite particles were investigated. Through analysis,the optimum conditions of the dispersibility of TiB2 particles in the TiB2 suspension are the first pretreated with HF (soaked 12h), then washed with deionized water until the pH=6.0.Treated deionized water, dubbed TiB2 powder volume fraction is 0.4% of the suspension, with the ultrasonic dispersion and pH=9, the appropriate of concentration(The molar ratio of A13+ to Y3+ is 5:3) of solution,titration speed for 2ml/min. Heat treatment of composite particles:high purely Ar; the reaction time is 1 h; the reaction temperature is the range of 900-1100℃. At last,the sintering densification of TiB2-YAG ceramics were investigated. Through analysis,the optimization sintering technology for preparing TiB2-YAG cermics with the hot press sintering is sintering temperature for 1600℃, sintering pressure for 30Mpa and holding time for 60min.Releative density of TiB2-YAG ceramics are increased with incresing YAG content.Relateive density. Microstructure can be even better performance ceramics, the relative density above 96%, bending strength up to 554MPa, Vickers hardness up to 19.68GPa.