Microstructure evolution and sequence of phase transition reactions through the solidification of Mo-Si-B alloy; a phase-field study

Abstract

The present study is focused on the phase evolution pattern and phase transition reactions between melt and arising solid phases during solidification of three different Mo-Si-B alloy compositions. To carry out this work, three alloy compositions from the Mo3Si, Mo5SiB2 and MoSS primary solidification regions, in the vicinity of ternary eutectic composition of Mo-Si-B system were selected. To investigate phase evolution and solidification reactions, a phase-field simulation is conducted with MicressTM applying the thermodynamic data generated with FactsageTM. The simulations confirmed the presence of binary and ternary eutectic reactions. It was observed that, depending on the initial melt composition, a primary phase emanates at the beginning of solidification which causes a composition fluctuation in the residual melt. Depending on the composition of the residual melt, thermodynamically feasible phases tend to perform a binary reaction until the rest of liquid undergoes the ternary MoSS-Mo5SiB2-Mo3Si eutectic reaction. However, exploring the solidification path of the considered compositions implied the uncertainties in considered thermodynamic parameters which requires the revision of thermodynamic database.