Experimental investigation and thermodynamic descriptions of the Mo–Si–Ti system

Microstructures and phase equilibria of the alloys in the Mo–Si–Ti system were studied in as-cast and long-term annealed conditions by imaging with back scattered electrons (BSE) in a scanning electron microscope (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD) analysis. Isothermal sections were established to describe the solid-state phase equilibria at 1600 and 1425 °C. Using the CALPHAD (CALculation of PHAse Diagram) approach, a thermodynamic data set of the Mo–Si–Ti system was optimized by considering both the present experimental results and reliable literature data. This thermodynamic modeling can satisfactorily account for the available experimental data. The liquidus surface near the metal-rich end of the Mo–Si–Ti system calculated from the present thermodynamic modeling is in good agreement with experimental observation. Two type-II invariant four-phase reactions were determined in the metal-rich region of the Mo–Si–Ti system. One is L+Mo(Ti)5Si3→Ti(Mo)5Si3+Mo(Ti)3Si, and the other is L+Mo(Ti)3Si→Ti(Mo)5Si3+β(Mo,Si,Ti).