Assessment of the high temperature deformation behavior of molybdenum silicide alloys

A novel method to manufacture a refractory metal three phase Mo-2.7%Nb-8.9%Si-7.7%B at.% silicide alloy with mechanical alloying as the crucial processing step is presented. After consolidation a triplex ultra-fine grained microstructure with the average sizes of the Mo solid solution and both intermetallic compounds Mo3Si and Mo5SiB2 (T2 phase), respectively, ranging clearly in the sub-micrometer range was obtained. Tensile tests revealed structural superplasticity with strain to failures as high as 400% and temperatures as low as 1300 °C. Due to the extraordinary thermal stability of the microstructure isothermal annealing at 1700 °C for 10 h was needed for significant coarsening of the microstructure. A comparative assessment of the compressive creep properties of both microstructures in the temperature range between 1050 and 1315 °C showed an increase of the creep resistance of the coarsened microstructure by more than one order of magnitude in strain rate compared with the material in the as-processed condition.