Boron Enhanced Complex Concentrated Silicides – A bridge between lightweight, oxidation-resistant Refractory Metal Silicides and Refractory Complex Concentrated Alloys

This study presents the Boron Enhanced Complex Concentrated Silicides (BECCSs) as a novel category of high-temperature materials derived from the high entropy concept. Using a quaternary MoNbTaW equiatomic alloy as a starting point, four new alloy compositions were designed in a multi-step process oriented towards reducing the density of the material. By incorporating different combinations of Ti, Si, and B, the phase composition of the materials was altered from a BCC solid solution to a multi-phase structure consisting of BCC solid solution and various intermetallics (silicides, borides, and borosilicides). The suggested modification of the alloy composition led to a significant decrease in density, reaching down to 6.87 g/cm3. All four alloys were fabricated by the arc melting technique, while their microstructure and room temperature mechanical properties were evaluated by SEM/EDS/EBSD and micro-indentation methods. The results of structural characterization enabled the identification of specific phase constituents. Consequently, it was established that the transition from BCC solid solutions to silicides/borides based alloys results in a significant increase in hardness, achieving up to 1200 HV (13 GPa).