Effect of particle size on the microstructure and mechanical properties ofRBBC ceramics

In this study, B۴C/SiC ceramic was prepared by infiltration of molten silicon into porous preformcontaining boron carbide and free carbon produced by uniaxial pressing under pressure of ۱۰۰MPa in a graphite furnace under vacuum ۳×۱۰-۵ torr. Here, effect of boron carbide particle sizeon the microstructure and mechanical properties such as hardness, fracture toughness andflexural strength of reaction bonded boron carbide (RBBC) ceramics were investigated. Afterreaction bonding with molten silicon, the experimental results show that ceramics comprise amixture of original B۴C particles, ternary boron carbide phase B۱۲ (B,C,Si)۳ at the surface of theoriginal boron carbide particles (core-rim structure), β-SiC within a residual silicon. Boroncarbide powders with mean particle size of ۲۵.۶۱ mm, ۴۳.۲۷ mm and ۴۶.۱۵ mm were chosen forthe RBBC ceramics. The experimental results show that hardness increases from ۲۰۵۰.۴۵kg/mm۲ to ۲۵۴۵.۷۰ kg/mm۲ and fracture toughness drops from ۶.۱ MPam۱/۲ to ۴.۲ MPam۱/۲.However, flexural strength decreases from ۴۵۵.۴۰ MPa to ۳۲۰.۱۵ MPa with the increase inparticle size. Smoothness for fracture surface increases with decreased particle sizes too. Thus,Maximum extent of non-planarity is observed at fracture path of RB-۱, medium for RB-۲ andlowest for RB-۳, and concurrently same type of behavior is observed in the deformation ofsilicon.

Keywords:

RBBC ceramics , Boron carbide , Infiltration , Particle size