BRITTLE-TO-DUCTILE TRANSITION TEMPERATURE AND ITS STRAIN RAf E SENSITIVITY IN Ti-47Al-2Mn-2Nb-0.8TiB_2
Ti—47Al—2Mn—2Nb—0.8TiB2合金韧脆转变温度及其应变速率敏感性

The effect of strain rate on the tensile yield strength and elongation of titanium aluminide has been studied. The alloy has a composition of Ti-47Al-2Mn-2Nb-0.8TiB2 (atomic fraction, %; volume fraction, %, only for TiB2) and near lamellar dricrostructure. It manifests brittle-to-ductile transition (BDT) at elevated temperature and its brittle-to-ductile transition temperature (TBDT) is positively sensitive to the strain rate. The addition of boron lowers the TBDT considerably, and the corresponding activation energy of BDT decreases to 256 kJ/mol, which is less than that of the alloy without boron (TiB2), but approximates the self-diffusion activation energy of atoms in the TiAl alloy. From additional fractography analysis and theoretical estimation, it is suggested that the BDT course of 7 titanium aluminide with the addition of boron (TiB2) is controlled by dislocation climbing.