Study On Microstructure And Properties Of Reaction Bonded TiB₂/SiC Composites

Reaction-bonded method basing on reaction-sintered silicon carbide for preparing titanium diboride ceramic composite materials possesses many advantages,such as relatively low sintering temperature,simple preparation process,near-net shape forming,industrialization available and low manufacturing cost,which has been attracting significant attention by researchers.However,residual silicon existing in the titanium diboride composite prepared by this method seriously impacts its mechanical properties and restricts its application range.In order to reduce the residual silicon in the reaction-bonded titanium diboride and improve its mechanical properties,the methods of gel casting,varying carbon content of preform and particle gradation were adopted.Better mechanical properties were achieved by reducing residual silicon in the composite.In this study,the effect of residual silicon on the microstructure and mechanical properties was systematically investigated.The results of this paper were of great theoretical and practical significance for improving the mechanical properties of TiB2 composites and expanding their application range.The main results of this paper are as follows:(1)The slurry with a solid content of 43.5 wt.%which was suitable for gel casting can be prepared,when the contents of the dispersant,curing agent and ethylene glycol were 1wt.%,1wt.%and 75wt.%(relative to resin and furfuryl alcohol),respectively.During the siliconizing process,carbon in the green body reacted with molten Si to form granular SiC grains,which are surrounded by titanium boride particles,forming composite materials with strong bonding force and dense structure.The composite materials that contain high residual silicon content consist of three phases of TiB2,SiC and Si.The flexural strength and fracture toughness of the TiB2 composites materials prepared by gel-casting were 161 MPa,3.6 Pa·m1/2 and 13 GPa,respectively.(2)The increase of carbon content in preform could significantly reduce the residual silicon in the composite and greatly improve the comprehensive mechanical properties of the material.When the carbon content was 30 wt.%,the mechanical properties of the composite were found to be the optimum,and the flexural strength,fracture toughness and Vickers hardness of which could reach 353 MPa,5.4 Pa·m 1/2 and 31 GPa,respectively;(3)The amount of residual silicon in the composite material could be further reduced when particle grading was adoped.When the mass ratio of the coarse particles and fine particles was 9:1 and the carbon content was 25wt.%,the bending strength,fracture toughness and Vickers hardness of the composite material could reach 379 MPa,5.9 Pa·m 1/2 and 28 Gpa,respectively.