Improvement in mechanical properties and high temperature oxidation resistance of j'TiAl intermetallic cOmpounds by boronising

Intermetallic compounds of λ-TiAl were boronised in the temperature ranges 1150 to 1250°C and 900 to 1050°C with B₄C powders and with powder mixtures of B₄C and Na₂B₄O₇ respectively. For specimens boronised with B₄C powders, substantial porosity was observed at the interface between the coating layer and substrate. The surface hardness of these specimens was ∼ 670 HV and was relatively insensitive to the boronising temperature and time. Boronising TiAl with B₄C powders improved both wear and high temperature oxidation resistance. Treatment with a powder mixture of B₄C and Na₂B₄O₇ resulted in higher quality coating layers on the TiAl substrate. The highest hardness (∼ 2720 HV) was obtained by a treatment at 900°C for 11 h. The wear and high temperature oxidation resistance of TiAl was more significantly improved than by boronising solely with B₄C.