Boride Formation, Microstructure Evolution, and Mechanical Properties of Ti42Al6Nb2.6C0.8Ta Alloyed by Boron

Abstract

In order to improve mechanical properties by grain boundary and precipitation strengthening, Ti42Al6Nb2.6C0.8Ta–xB (at%) alloys with x = ranging from 0 to 2.0 at% are prepared by vacuum arc melting. Microstructure evolution especially boride formation and mechanical properties of these alloys are studied. The results show that volume fraction of TiB particles increases and volume fraction of B2 phase decreases with increasing content of B. Three morphologically different types of boride particles are identified in the studied alloys: granular (C), plate (P), and flake (F). Volume fraction of F type borides increases remarkably with increasing content of B. Lamellar colony size decreases with increasing content of B up to 0.8 at%. Lamellar colony size increases with increasing content of B above from 0.8 to 2.0 at%. Compressive strength increases from 1710 to 2084 MPa and compressive strain increases from 10.6 to 19.0% with increasing content of B. Ultimate tensile strength increases from 426 to 613 MPa and tensile strain increases from 3.4 to 4.6% at 750 °C with increasing content of B. Precipitation strengthening by TiB, decreasing of volume fraction of B2 and increasing volume fraction of γ phase are mainly responsible for improvement in mechanical properties.