High temperature creep behavior of thixoformed nickel-based superalloy parts

In this paper, nickel-based superalloy disk parts were fabricated by semi-solid thixoforming, and some of them were subjected to standard heat treatment. High temperature creep properties of the thixoformed parts before and after heat treatment were studied. The effects of temperature and stress on the microstructure and steady state creep rate were investigated. The results exhibited that heat treatment had a positive influence on the initial microstructure and creep properties of the thixoformed parts. The creep life and creep strain of the specimen without heat treatment at 850 ?C/196 MPa were 28.3 h and 3.3%, respectively. After heat treatment, the creep life and creep strain of the specimen increased to 52.7 h and 9.9%, respectively. The steady state creep rate increased with the increase of temperature and stress. The microstructure observations indicated that the creep process had little effect on the morphologies and compositions of the grain boundary carbides, while it promoted the growth of the ?? precipitates. With the increase of temperature and stress, the average diameter of ?? precipitates increased. At 850 ?C/196 MPa, the dislocations tended to pass the ?? precipitates through Orowan looping mechanism. The creep fracture of the specimen without heat treatment was mainly intergranular fracture, while the transgranular fracture was dominant after heat treatment.