Ab initio study of the effect of solute atoms on vacancy diffusion in Ni-based superalloys

T Technology > TN Mining engineering. Metallurgy

Goswami, Kamal Nayan ; Mottura, Alessandro,Basoalto, Hector

University:University of Birmingham

Department:School of Metallurgy and Materials

关键词: T Technology;    TN Mining engineering. Metallurgy;   

Others  :  http://etheses.bham.ac.uk//id/eprint/8509/1/GoswamiPhD18.pdf

来源: University of Birmingham eTheses Repository

【 摘 要 】

Single crystal Ni-based superalloys are used in the highest temperature components in jet turbine engines owing to their excellent properties under creep conditions. These alloys owe their properties greatly to their chemical composition, and in particular the addition of slow diffusing elements like Re delays the creep deformation significantly. Vacancy diffusion has been suggested to be the rate-controlling process for creep deformation at high temperatures, and elements like Re are expected to interact with the vacancies in slowing them down. This has been investigated in the present work using ab initio calculations. Specifically, dilute as well as non-dilute binary alloys of Re, W and Ta in Ni were considered to study the effect of chemical composition on the rate of vacancy diffusion. Analytical formulations were used to describe the diffusion equations, however their applicability was restricted to the dilute regime. For the calculation of diffusion coefficients particularly in the non-dilute regime, kinetic Monte Carlo simulations were performed. The energies and the diffusion barriers were described using the cluster expansion method. Results suggested appreciable modifications of the vacancy diffusion coefficients, suggesting that the beneficial role of slow-diffusing elements in Ni-based superalloys could be partly explained by their effect on vacancy diffusion.