AN ATTRACTIVE WAY TO HEAL SURFACE-DEFECTS OF SOME CARBIDE AND BORIDE CERAMICS

An effective way to heal surface cracks and surface-connected pores of some carbide and boride ceramics is theoretically proposed and experi mentally confirmed in this paper. The theoretical calculations have in dicated that the surface defects of some carbide ceramics such as NbC, SiC, Cr3C2 and B4C as well as several boride ceramics such as TiB2, Z rB2, NbB2 and TaB2 may be healed by a nitriding process. The experimen tal results have shown that the indentation cracks on the polished sur face of hot isostatically pressed SiC ceramics and hot-pressed SiC-TiC multiphase ceramics can be healed to a large extent by nitridation un der an N-2-pressure of 2000 arm at 1850 degrees C for 1 h. Further, th e contents of surface-connected pores were determined to decrease from 4.5 and 7.5% to 0.3 and 0.4% for SiC and SiC-TiC multiphase ceramics after nitridation.