Influence of oxygen on microstructure and mechanical properties of directionally solidified Ti–47Al–2Cr–2Nb alloy

The effect of oxygen on the microstructure of directionally solidified (DS) Ti–47Al–2Cr–2Nb alloy was investigated. The DS Ti–47Al–2Cr–2Nb ingots with oxygen contents ranging from 180 to 2360 wt. ppm were obtained in the electromagnetic cold crucible. Increasing the oxygen content led to a change of primary solidification β phase to α phase and finally the volume fractions of lamellae with the orientation normal to the growth orientation would then increase. In addition, the decrease in oxygen content resulted in an increase in the volume fraction of α2 phase, which led to a decrease in the interlamellar spacing of the lamellar structure. DS Ti–47Al–2Cr–2Nb alloy with lowest oxygen content exhibited a bit lower Vickers microhardness and the yield strength while showed highest ductility at room temperature.

► Increasing of oxygen content led to a change of primary solidification phase.
► Volume fractions of vertical aligned lamellae increased with increase of oxygen.
► α2 volume fraction increased and lamellar space decreased with increase of oxygen.
► Yield stress increased while ductility decreased with increasing oxygen content.