Mo–Si–B alloys for ultra-high-temperature space and ground applications: liquid-assisted fabrication under various temperature and time conditions

Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high temperature applications far beyond limits of state-of-the-art nickel based superalloys. In this work, we are exploring a new method for fabricating Mo-Si-B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si-B melt with molybdenum . The main purpose of this work, was to examine the effect of temperature and time of Si-B melt interaction on the structure and morphology of the formed reaction products. For this purpose, sessile drop experiments were carried out on the eutectic Si-3.2B (wt%) alloy/Mo couples at temperature varying between 1385-1550°C and holding time between 10 to 30 minutes. The solidified sessile drop couples were subjected to microstructural characterization by means of light microscopy and scanning electron microscopy analyses performed both at "top-view" and cross-sectioned interfaces. The phases formed within the interaction zone were identified by using TEM/SAED and XRD techniques. It was documented that a thickness of both main product layer (MoSi2+Mo5Si3), as well as boron-rich interlayer increases with raising temperature and time of the Si-B melt interaction with Mo substrates.