Preparation And Properties Of B₄C Reinforced TiB₂ Based Ceramic Composites

TiB₂ ceramic is one of the most popular non-oxide ceramics.It has not only high melting point,high hardness,good chemical stability and wear resistance,but also excellent electrical conductivity.TiB₂ ceramic has potential applications and could be used as thermal protection materials,wear-resistant parts,high-temperature electrical components,inert electrode materials and so on.Due to the difficulty in sintering of monolithic TiB2 ceramic,it has become a hot topic to investigate the TiB₂ based composites by introducing secondary phases.In this thesis,B₄C reinforced TiB₂ based ceramic composites were studied.The main contents and results were as follows:?1?Ti B₂?B₄C composite ceramics were prepared by hot-pressed sintering at 1900 ^oC/35MPa for 1 h using commercial TiB₂ and B₄C powders as raw materials,and the effects of B₄C particle size?0.50?m,3.12?m and 7.09?m?and the content of B₄C?10 vol.%,20 vol.%and30 vol.%?on the phase composition,microstructures and mechanical properties of as-prepared TiB2?B4C ceramic were investigated.The results indicated that the addition of B4C particles to TiB₂ matrix inhibited the orientated growth of TiB₂ grains during the hot-pressed sintering process.When the content of B₄C in the composite was 10 vol.%,B₄C powder with a particle size 0.50?m had the best inhibitory effect on the orientated growth of TiB2 grains.When the content of B₄C in the composite was 20 vol.%or 30 vol.%,B₄C powder with a particle size7.09?m had the best inhibitory effect.The particle size of B₄C powder had significant effects on the densification of TiB2?B4Cceramics.When the particle size of B4C powder was 0.50?m,although the relative densities of the obtained ceramics were much higher than that of monolithic TiB₂ ceramic?87.50%?,the maximum value was only 97.19%.When the particle size of B₄C powder was 3.12?m or 7.09?m,the obtained ceramics were nearly or fully densified.When the particle size of B4C powder was 3.12?m,the obtained TiB2?30 vol.%B4C ceramic exhibited the best mechanical properties with a flexural strength of 671 MPa,a Vickers hardness of 27.93 GPa and a fracture toughness of 3.91 MPa?m^1/2,respectively.?2?TiB2?30 vol.%B4Ccomposite ceramics were prepared by reactive sintering at 1900^oC/35 MPa for 1 h using commercial TiB₂,TiC and amorphous B powders as raw materials,and the effects of TiC particle size?0.05?m,0.80?m and 3.00?m?on the phase composition,microstructure and mechanical properties of as-prepared ceramics were investigated.The results indicated that no impurity was found in the obtained ceramics when the B was 10%in excess.The particle sizes of TiC powders had different effects on the orientated growth of TiB₂grains during the sintering process.When the particle size of TiC powder was 0.05?m,the effect of inhibitory effect on the orientated growth of TiB2 grains was the best,the 3.00?m Ti C powder was the second,and the 0.80?m TiC powder was the worst.When the particle size of TiC powder was 0.80?m,the size distribution of TiB₂ and B₄C grains in the obtained ceramics was the narrowest,which resulted the best mechanical properties with a flexural strength of 636MPa,a Vickers hardness of 27.78 GPa and a fracture toughness of 6.03 MPa·m^1/2,respectively.