Role of stabilization heat treatment inducing γ′-γ" co-precipitates and grain boundary η phase on tensile and creep behaviors of Inconel 706

The effects of the stabilization conditions on the microstructure evolution in Ni-Fe-based superalloy Inconel 706 were investigated. In addition, the relationship between the microstructure and tensile and creep properties of the alloy was investigated. Stabilization at 800-840 degrees C resulted in the precipitation of the eta phase at the grain boundaries. With an increase in the stabilization temperature, the eta phase fraction increased. Non-compact gamma'-gamma '' co-precipitates were also formed at 800-840 degrees C, and their size was the largest when the stabilization was carried out at 840 degrees C. After double aging, the sample stabilized at 840 degrees C showed a cuboidal gamma' phase covered entirely with gamma '' films, i.e. compact gamma'-gamma '' co-precipitates were observed along with a coarsened lamellae eta phase. The double-aged sample stabilized at 800 degrees C (S80) exhibited the highest yield strength because of the presence of fine gamma' and gamma '' precipitates. The double-aged samples stabilized at 810 and 840 degrees C (S81 and S84, respectively), exhibited similar yield strengths. Isolated stacking faults were generated in the gamma' particles of the S81 and S84 samples during the tensile deformation, indicating the high mobility of perfect dislocations in the gamma-matrix. After creep at 650 degrees C/650 MPa, S81 and S84 exhibited higher creep strain at a given time than S80. This higher creep strain can be attributed to the synergistic effect of the increased dislocation mobility and eta phase fraction, which resulted in strain accumulation at the grain boundaries. The anti-phase boundary shearing observed only in the S84 sample contributed to the strengthening of its gamma-matrix and increased its creep rupture life. (C) 2021 Elsevier B.V. All rights reserved.