Investigation of creep deformation mechanisms and environmental effects on creep resistance in a Ti2AlNb based intermetallic alloy

Creep deformation mechanisms and environmental effects of Ti2AlNb based intermetallic alloys are investigated. Two different creep deformation mechanisms operate in accordance with elevating temperatures in the range of 600–800 °C. Below 700 °C, dislocation climb by pipe-diffusion may control the creep deformation. A sharp drop of creep resistance is observed above 700 °C in an air environment. This abnormal acceleration in creep rate may be due to the abundant supply of easily mobile dislocations on the prismatic plane provided by the bcc to O phase transformation. Therefore, the creep deformation mechanism above 700 °C may be considered to be the bcc to O phase transformation that generates prismatic dislocations. The creep resistance in a vacuum environment is superior to that in the air environment, especially at temperatures above 700 °C. This may be because the limited oxygen level in a vacuum environment can keep the bcc phase stable at such temperatures. Therefore, prismatic dislocations to control and accelerate creep rate above 700 °C are not supported by the bcc to O phase transformation and the creep resistance can be enhanced.