2009 Volume 50 Issue 7 Pages 1644-1648
Electric field treatment was performed on a Ni-Cr-W-Mo superalloy to investigate the effects of electric field treatment on its corrosion behavior. The microstructure evolution and the elements distribution at grain boundaries of both annealing twins and high angle grains were examined. The results show that the corrosion resistance can be improved by the electric field treatment and both of the corrosion weight loss and corrosion rate are decreased with the increasing treating time. When the alloy is electric field treated at 1093 K for 600 min with 4 kV·cm−1, the intergranular corrosion rate is 65.3 mm·y−1 with the decreasing ratio of 25.1% compared with the untreated one, and the immersion corrosion rate is 3.9 mm·y−1 with the decreasing ratio of 57.9% compared with the untreated one. The redistribution of elements between the original high angle grain boundaries and the annealing twins occurred by the formation and growth of the annealing twins during the electric field treatment, as well as the improvement of exhaustion of Cr and Mo elements at the grain boundaries. With the increasing treating time, a large amount of original high angle grain boundaries are replaced and the continuously distributed original grain boundaries are separated, which leads to the retardation the growth rate of the corrosion ditches. The corrosion resistance of the alloy is improved due to the changes of corrosion behavior of the grain boundary. Moreover, the promotion effect of electric field treatment on the atom diffusion rate decrease the exhaustion tendency of Cr and Mo elements on both sides of normal high angle grain boundary. Those can be considered as the reasons of improving the corrosion resistance after electric field treatment.
