The effect of refractory metal substitution on the stability of Mo(ss) + T-2 two-phase field in the Mo-Si-B system

The influence of refractory metal substitution such as Nb and Cr for Mo in Mo-B Si alloys on the phase stability has been examined for compositions in the Mo(ss) + T-2 two-phase held. The solidification pathways as well as the width of the two-phase field at high temperature are modified by refractory metal substitutions. The characteristically severe solidification segregation found in Mo-B-Si alloys may be significantly reduced if the substitution such as Nb for Mo change the T-2-phase lattice constants to facilitate a larger compositional exchange between B and Si in the T-2 phase. The enhanced B and Si exchange also yields a significant increase in the width of Mo(ss) + T-2 two-phase field. This behavior highlights the role of atomic size factor in influencing the relative stability of the T-2 (D8(i)) phase. (C) 2001 Elsevier Science Ltd. All rights reserved.