COMPRESSIVE CREEP-BEHAVIOR OF MO5SI3 WITH THE ADDITION OF BORON

Mo5S3 shows high creep resistance but poor high temperature oxidation resistance. Previous work has shown that the oxidation rate of Mo5Si3 can be decreased with the addition of boron. By adding 1 3 wt % boron to a silicon deficient composition, a three phase microstructure compo sed of Mo5Si3 (T1), Mo5Si3, and a ternary Mo-5(Si,B)3 (T2) phase was s ynthesized. The compressive creep rate of this composition was evaluat ed at 1240-1320 degrees C and 120-180 MPa. The average creep stress ex ponent and activation energy for the three phase material were found t o be n = 4.3 and E(a) = 396 kJ/mol. TEM analysis of the crept microstr ucture of the boron modified material reveals no evidence for dislocat ion activity in T1. Only basal slip was observed in the T2 phase while polygonal sub-grain structures were observed in Mo3Si. (C) 1996 Elsev ier Science Ltd.