W,Mo Doping On Nickel Base Superalloy A First-principles Study Of The Effects Of γ’ Phase

Nickel-based superalloys are used in a wild fields,because of its excellent high temperature resistance,meet the requirements of service in harsh environment.W,Mo as the main strengthening elements of the alloy,the distribution behavior in γ phase and γ’phase has a great impact on the durability of nickel base alloy.In this thesis,based on density functional theory,the effects of doping atoms W and Mo on the geometrical structure and electronic structure of γ’ phase,as well as the effects of W and Mo atoms on the interfacial vacancy and diffusion of γ/γ’ phases are systematically studied.Through the preliminary experimental data,The Al/Ti ratio in γ’ phase is about 0.66.In this thesis,two γ’ phase structure models with Al/Ti ratio of 3/5 and widely used 1/1 are used to explore the common law.The effect of alloying elements W and Mo on the stability of γ and γ’ phases was obtained by using the formula of substitution formation energy calculated by the First Principles.By calculating the charge density and the state density,the undoped,doped W and doped Mo structures will be compared.The influence of doping on the adsorption energy at γ/γ’ phases interface was further studied on the basis of W and Mo occupying tendency best.It is found that the interfacial stability of the doped atoms at γ’ phase is improved greatly.Compared with the doped atoms at γ’ phase,the adsorption energies of the doped W and Mo interfaces are increased by 0.72 eV/nm2 and 0.6 eV/nm2 respectively,and the stability of the doped W at γ/γ’ phase interface is increased by 20%.The factors that makeγ/γ’ interface more stable due to W doping and the reason why W is not easy to be replaced are studied.The diffusion behavior of W and Mo at γ/γ’ phases interface was calculated by using CI-NEB module in VASP.The distribution behavior of W and Mo atoms between the two phases was analyzed by comparing the vacancy formation energy and diffusion barrier before and after diffusion.The results show that the vacancy formation energy of Ni atoms is 0.13 eV higher with γ/γ’ phases interfacial doping W.The diffusion barrier of γ/γ’phases interfacial diffusion W is about 15.6%higher than Mo.And the inverse diffusion barrier of γ/γ’ phases interface is about 19.6%higher than that of Mo.The study 1 mentioned above shows that W atoms diffused into γ’ phase are more stable,and it is difficult to get back into γ’ phase by diffusion.Therefore,the amount of W atoms of entering γ’ phase continues to increase,resulting in the difference in the distribution of W and Mo in γ’ phase.