Effect of Pd addition on the microstructure of Ti-30Nb alloy

Abstract

The effect of Pd addition on deformation mechanisms, phase transitions and twinning has been extensively investigated in as-cast β-type Ti-30Nb (wt%) alloy using electron backscattered diffraction and transmission electron microscopy techniques. The addition of Pd resulted in refinement of the metastable ω phase. The {112} -type twinning was found to strongly depend on the size of the ω particles. No β phase twins were observed in the binary alloy with larger ω particles. In the ternary alloy with much finer ω particles, {332} and abundant {112} -type twins were detected. On the contrary, the volume fraction of stress-induced α“ martensite in the binary alloy was higher than that in the ternary one. Based on the analysis of phase diagrams and Gibbs free energy calculations, such complex phase transition and twinning phenomena have been explained in terms of relative phase stability between the ω particles and the β matrix.