Creep behavior and deformation mechanisms of a novel directionally solidified Ni-base superalloy at 900 °C

Abstract

A novel directionally solidified Ni-base superalloy with excellent creep-rupture strength has been developed. By means of measurement of the creep properties and microstructural observations, the variations of the creep deformation behavior and corresponding deformation mechanisms of the new superalloy with the applied stress are investigated at 900 °C. As the applied stress increases from 300 to 375 MPa, the steady-state creep rate increases gradually, whereas the creep-rupture life decreases. Transmission electron microscope observations on the crept specimens reveal that dislocation climb plays an important role in the steady-state creep deformation, and the process which two matrix dislocations with different Burgers vectors combine into one a〈001〉 dislocation and subsequently shear through γ′ precipitates operates more actively with increasing the applied stress. Based on the experimental observations, the reasons that account for the variation of the creep properties with the applied stress are discussed.