Abnormal acceleration of creep deformation rate above 700 °C in the orthorhombic based Ti–22Al–27Nb alloy

Abstract

For the past decade, Ti 2AlNb-based alloys have been investigated for being applied to the structural materials in aerospace engine. In this study, creep tests of Ti–22Al–27Nb (at.%) alloys are conducted at a constant tensile stress of 200 MPa at the various temperatures in the range from 650 to 750 °C. It is observed that the creep deformation rate of the O+bcc dual phase alloys is abnormally increased at temperatures above 700 °C. The results of TEM investigation show that the active slip systems are varied and the density of dislocation is increased with increasing temperature above 700 °C. In this temperature range, prismatic dislocations in the orthorhombic phase are newly generated from O–bcc interfaces by the result of phase transformation and the movement of the prismatic dislocations is very active compared to the basal slip system. Therefore, it is suggested that the phase transformation of bcc to O phase activates another slip system by the abundant supply of actively moving dislocations, thereby accelerating creep deformation rate at the elevated temperature above 700 °C.