Effects of pre-compression on the stress rupture properties of Ni base single crystal superalloy DD98 and its mechanism

The effects of uniaxial pre-compressions in vacuum at 1050 degrees C by 180 MPa/6 h and 220 MPa/6 h on the microstructure and stress rupture properties of single crystal superalloy DD98 were investigated. It is shown that P-type gamma' raft parallel to stress formed during pre-compression. Moreover, dislocation networks appeared on gamma/gamma' interface in vertical channels. The effect on stress rupture lifetime varied with the test conditions, but the pre-compression increased the elongations under all test conditions. Under high-temperature and low-stress, the pre-compression made P-type raft transform into wave-like N-type raft with different widths in two samples, and dislocations overpass gamma' particles by different means. Under low-temperature and high-stress the P-type raft showed only a slight tendency to transform into N-type one, and the entangled dislocations appeared in two precompressed samples after stress rupture. Under intermediate temperature and stress, the P-type raft can still transform into N-type one but very irregular, and the dislocations formed irregular networks.