Structure and properties of metal-boride eutectic alloys of Ti—Mo—B and Nb—Mo—B systems

Abstract

Structure and physico-mechanical properties, microhardness at room temperature and Vickers hardness in the temperature range of 20—900 °C were studied for metal-boride eutectic alloys of Ti—Mo—B and Nb—Mo—B systems. As established, partial stabilization of the phase based on β-Ti by Mo leads to formation of multicomponent matrix β + α″ + ω at [Mo]/([Ti] + [Mo]) = ~0,05 (contents of metals are in % (at.)) that results in maxima in curves of concentration dependences for microhardness and hardness. Maximum strengthening of the β-matrix (to 6,1—6,9 GPa) was observed in the range of 0,45 < [Mo]/([Ti] + [Mo]) < 0,8. Temperatures of incipient sharp softening of Ti—Mo—B alloys were found to be practically unaffected by the metal ratio in the range of multicomponent matrix and to increase by approximately 200 °С for the β-matrix alloys. Microhardness of eutectics in Nb—Mo—B alloys increases with the Mo content increase, from 9,4—12,6 GPa for the β + (Nb_1-xMo_x)₃B₂ eutectic to ~15,6 GPa for β + (Nb_1-xMo_x)₃B₂ + (Mo₂B) one and to 1,9 GPa for β + (Mo₂B).