Research On TiB₂-based Ceramic Tool Material Toughened By Whiskers

TiB2 ceramics have the advantages of high strength and hardness,strong oxidation resistance,etc.,but single-phase TiB2 ceramics a low free diffusion coefficient and poor sintering density,resulting in low fracture toughness and bending strength,which limits widely used and developed as a ceramic tool material.Under the guidance of the existing sintering theory and toughening and strengthening theory,this paper uses carbothermal reduction method to synthesize TiC whiskers,using TiB2 as the matrix,TiC whiskers as the additive phase,and metals Ni and Mo as sintering aids.TiB2-TiCw composite ceramic tool material was prepared by pressure sintering process.Under the theoretical guidance of traditional carbothermal reduction and preparation of TiC whiskers,in order to solve the problem of excessive free carbon in the prepared whisker powder,C6H12O6·H2O was proposed to replace part of the molar amount of C as the raw material for the preparation of TiC whiskers.The optimal molar group distribution ratio of TiC whiskers is TiO2:C:C6H12O6·H2O:Ni:NaCl=1:2.1:0.15:0.05:0.5.The influence of sintering process on the production and morphology of TiC whiskers was optimized,and the best preparation process of TiC whiskers was determined as follows:heating for 40min to 1500?,holding for 60min,heating at 5min to 1600? for two times,and holding for 30min.The growth mechanism of TiC whiskers has been studied.The experiments show that the growth process of the whiskers conforms to the SLLS growth mechanism.Ni droplets continuously consume solid reactants,and the reaction raw materials are continuously transported to the vicinity of the Ni droplets through the adhesion and evaporation of NaCl itself,thereby promoting the continuous growth of TiC whiskers.The phase composition of successfully prepared TiC whiskers and the factors affecting the yield and aspect ratio were analyzed.The experiment optimized the effect of the material's composition ratio and sintering process on its mechanical properties and microstructure.Experimental research shows that the optimal group distribution ratio in the composite ceramic tool material:the optimal content of the added phase TiC whiskers is 30%,and the optimal addition amount of the sintering aid is Ni6.5vol.%and Mo3.5vol.%.The optimal sintering scheme for preparing TiB2-TiCw composite ceramic tool materials was determined:heating for 30min to 1310?,30min to 1700?,holding for 30min,sintering pressure of 30MPa,argon gas as the protective atmosphere throughout the sintering process,its comprehensive mechanical properties are the most The bending strength is 860MPa;the fracture toughness is 7.9MPa·m1/2;the Vickers hardness is 22.56GPa.Three toughening mechanisms of TiB2-based composite ceramic tool materials toughened by whiskers were studied:crack deflection,whisker bridging,and whisker extraction.The main factors influencing the toughening of whiskers are summarized and analyzed:the content and aspect ratio of whiskers,the arrangement of whiskers,and the bonding force between the whiskers and the substrate.