Stability and Properties of the Solid Solutions Based on Carbides, Borides and MAX Phases

A plausible mechanism of stabilization or destabilization of the solid solutions (alloys) based on transition metal (TM) carbides, borides and MAX phases is suggested using the results of first-principles calculations of the Ti1-xHfxC, Ti1-xTaxC, Ti1-xZrxC, Ba1-xLaxB6, and Ti2Al1-xSixC alloys. It was established that the alloying of the end members with different valence electron concentrations (VEC) leads to a change of the occupancy of the metal band. As a result, the mixing energy of the solid solutions is negative, i.e. the alloys are stable relatively the end members. On the contrary, the solid solutions are unstable relatively the end members with the same VECs. The stable alloys exhibit a positive deviation of the Vickers hardness from linearity.