IMPROVEMENT IN MECHANICAL-PROPERTIES AND HIGH-TEMPERATURE OXIDATION RESISTANCE OF GAMMA-TIAL INTERMETALLIC COMPOUNDS BY BORONISING

Intermetallic compounds of gamma-TiAl were boronised in the temperatur e ranges 1150 to 1250 degrees C and 900 to 1050 degrees C with B4C pow ders and with powder mixtures of B4C and Na2B4O7 respectively. For spe cimens boronised with B4C powders, substantial porosity was observed a t the interface between the coating layer and substrate. The surface h ardness of these specimens was similar to 670 HV and was relatively in sensitive to the boronising temperature and time. Boronising TiAl with B4C powders improved both wear and high temperature oxidation resista nce. Treatment with a powder mixture of B4C and Na2B4O7 resulted in hi gher quality coating layers on the TiAl substrate. The highest hardnes s (similar to 2720 HV) was obtained by a treatment at 900 degrees C fo r 11 h. The wear and high temperature oxidation resistance of TiAl was more significantly improved than by boronising solely with B4C. (C) 1 998 The Institute of Materials.