TOUGHENING B₄C CERAMICS BY TiB₂ PARTICLES PRODUCED IN SITU B₄C

Fine TiB₂ particles are produced in situ-B₄C through reaction of B₄C + 2TiC=2TiB₂+3C and B₄C-based composites are prepared by hot-press process at 2050℃. The composite derived from B₄C-20vol% TiC has a peak KIC value of 6.3MPa·m^1/2,which is higher than that of monolithic B₄C by 75%. The material resulting from B₄C-10vol%TiC enjoys a maximal bending strenght of 620MPa,which is 40% higher than that of monolithic B₄C. The crack denection and microcrack toughening caused by the residual stress resulting from the difference in thermal expansion coefficient between B₄C and TiB₂ are the main toughening mechanisms. The carbon derived from the reaction is one reason for the decrease in bending strength and Vickers hardness.