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

Abstract

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 field. 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 ℓ) phase.