Thermodynamic description of the Ni-Mo-W system and interdiffusion study of its fcc phase

The thermodynamic description of the Ni-Mo-W system has been updated and thereafter the ternary fcc Ni-Mo-W diffusion couples annealed at 1473 K for 72 h have been scanned to measure the composition profiles by using electron probe microanalysis (EPMA). By analyzing the composition profiles using the Whittle-Green method, the interdiffusion coefficients were deduced at the intersections of every two diffusion paths. These data were then combined with the thermodynamic description to determine the diffusion mobilities of Ni, Mo and W by means of DICTRA software. The calculated composition profiles and diffusion paths were carefully compared with the experimentally measured data, and an excellent agreement has been achieved. A previous conclusion that Mo diffuses faster than W in the Ni-base alloys was confirmed in the present work. In addition, Co promotes the diffusion of Mo whereas both Cr and W retard its diffusion in the Ni-base alloys containing 5.0 at% Mo. Both Co and Mo retard the diffusion of W in the Ni-base alloys containing 5.0 at%W.