Integrative Materials Design of Three-Phase Mo-Si-B Alloys

Abstract

Mo-Si-B alloys can offer higher temperature capability than Ni-base superalloys with proper balancing of the creep, ductility, and oxidation resistance through microstructure optimization. Mo-Si-B alloys are heterogeneous, containing both brittle and ductile phases and interfaces. Therefore, the phase fractions, their distributions, and their constitutive properties over the range of room temperature to maximum use temperature must be considered. This work addresses the optimization of mechanical properties for three-phase Mo-Si-B alloys. Three modeling tools are employed: microstructure generators to re-create statistically realistic microstructures, crystal viscoplasticity constitutive equations implemented for use with finite element solvers to capture microplasticity, and reduced-order models for evaluating important mechanical properties. In particular, the effects of microstructure on elastic modulus, yield strength, fatigue resistance, and susceptibility to brittle microcracking are considered. A novel reduced-order model is introduced for the evaluation of susceptibility to microcracking at phase interfaces. It is found that the Si content of the α-Mo phase is much more significant to the alloy’s balance of mechanical properties than the α-Mo volume fraction.