| TiB2 ceramic has the advantages of high hardness,high melting point and good conductivity,but its low fracture toughness and brittleness limit its further development and application.In this paper,the toughness and flexural strength of TiB2 based ceramic tool materials are improved by whisker toughening.According to the principles of physical and chemical compatibility of composite ceramic tool materials,TiC whiskers are chosen as toughening phases,Ni and Mo as metal phases.According to the toughening mechanism and sintering mechanism of composite ceramics,a new type of TiB2-TiCw composite ceramic tool material has been successfully developed by liquid phase hot pressing sintering process.TiO2,C,NaCl and Ni were selected as raw materials for synthesizing TiC whiskers by carbothermal reduction.The growth mechanism of TiC whiskers synthesized by carbothermal reduction was studied.The Ni droplet plays a role in the growth of the whisker as the catalyst phase.As a mass transfer phase,NaCl can feed the Ni droplets by adhesion and self evaporation to ensure the continuous growth of the whisker.Optimization design was carried out on the preparation technology of whisker.The best growth process of whiskers is to keep 60min at 1500? and then heat up to 1650 C in 10min,held for 30min.Short time high temperature ignition helps to reduce impurities such as free carbon in whiskers.The macroscopic defects of whiskers and their causes are analyzed,and the factors that influence the yield and length ratio of whiskers are analyzed.The driving force of TiB2 ceramics sintering is studied,and the reduction of its surface energy provides impetus for sintering densification.The mechanism of solid-phase sintering,the mechanism of liquid phase sintering and the densification mechanism of TiB2 ceramics were studied.The factors affecting the sintering of TiB2 ceramic tool materials were analyzed,and the sintering characteristics were also studied.The preparation process of whisker reinforced TiB2 based ceramic tool material composite powder was studied,and the experimental scheme of the material was determined.TiC whiskers were dispersed by mechanical stirring and ultrasonic vibration.Under the sintering process of sintering temperature of 1700?,heat preservation time 30min and sintering pressure of 32MPa,the comprehensive mechanical properties of TiB2 composite ceramic tool materials are best,and their bending strength,fracture toughness and Vivtorinox hardness are 832Mpa,7.42 MPa·m1/2,23.12GPa respectively.The synergistic toughening of TiB2 ceramic tool materials with TiC whiskers and TiC particles is proposed.The toughening and strengthening mechanism of TiC whisker was studied,and its toughening and strengthening mechanism was analyzed. |
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