Correlation microstructural evolution with creep-rupture properties of a novel directionally solidified Ni-based superalloy M4706

摘要

After isothermal aging at 850 degrees C for different hours, the microstructures as well as creep-rupture properties of a novel directionally solidified Ni-based super-alloy M4706 are studied under the condition of 980 degrees C and 180 MPa. We found that the mean edge length of gamma' particles only increases up to 484 +/- 99 nm after the aging treatment of 850 degrees C/5000 h, and the corner of the gamma' particle becomes more and more rounded with particle size, whereas the gamma' volume fraction remains unchanged with time. At grain boundaries, the carbide film, which is consisted of MC and M23C6 carbides, is produced after thermal exposure for 1000 h, and its content increases with time. Creep-rupture tests reveal that the creep-rupture life is reduced only from 180 +/- 15 to 106 +/- 15 h, and the elongation to fracture decreases from 32 +/- 2% to 21 +/- 1% after isothermal aging for 5000 h. Microstructural observations disclose that creep deformation is achieved mainly by dislocation climb, although shearing of gamma' particles by pairs of a/2 dislocations also takes place occasionally. Based on the experimental results, the relationship between the creep-rupture properties and microstructures together with the creep deformation mechanisms is discussed. [GRAPHICS] .