Study On The Diffusion Behavior And Atomic Mobility Of Alloying Elements In The β Phase Of The Ti-V-Cr And Ti-V-Mo Ternary Systems

Titanium alloys have high specific strength,low elastic modulus,excellent corrosion resistance and biocompatibility,and are widely used in aerospace,automotive,medical and other fields.With the rapid development of related industries,titanium alloys are bound to face more severe service environment,and there is a strong demand for new titanium alloys with better performance.The diffusion of related alloy elements affects many properties of metal materials during processing and service,such as phase transformation,homogenization treatment,welding and creep.In order to efficiently design the composition and heat treatment process of the multi-element titanium-based alloys,it is necessary to know the diffusion behavior in the alloys.However,there is little research on the diffusion behavior of the elements in the titanium alloy ternary system.Therefore,based on the CALPHAD method,this paper uses the diffusion couple method to study the diffusion behavior of alloy elements in the β phase of the Ti-V-Cr and Ti-V-Mo systems.Combined with the experimental data and computer technology,the atomic mobility parameters of the Ti-V-Cr/Mo ternary alloy were evaluated and optimized,and the kinetic database of the titanium alloy was improved.This work mainly includes:(1)According to the relative phase diagram of the system,Ti-V-Cr/Mo ternary alloy samples were prepared by the diffusion couple method.The composition profile of the diffusion couple was obtained by electron probe technology,and the scattered experimental points were fitted to a smooth curve through the error function.Then the interdiffusion coefficient and impurity diffusion coefficient of titanium alloy were extracted.The results show that the main diffusion coefficient of each alloy element is about 10 times of its cross-diffusion coefficient,which indicates that the diffusion characteristics of each alloy element in the β phase of Ti-based alloy are mainly determined by its own composition content,while the content of other elements has a weak influence on the diffusion behavior of another element.Comparing the interdiffusion coefficients of elements in the two systems,it is found that Cr has stronger diffusivity in Ti-V-Cr alloy β phase than V,while V has stronger diffusivity in Ti-V-Mo alloy β phase than Mo.The higher the temperature,the larger the diffusion coefficient of elements,and the higher the temperature,the faster the diffusion of V,Cr and Mo in the alloy.(2)Based on the relevant thermodynamic and kinetic parameters published in the literature,combined with the diffusion coefficients obtained in this work,the atomic mobility parameters of the Ti-V-Cr/Mo ternary alloy system were optimized in the Thermo-Calc software,and the optimized atomic mobility parameters were used to simulate the composition-distance curves of each diffusion couple.The simulation results are in good agreement with the experimental results.It is proved that the atomic mobility parameters obtained in this paper can be used to build a kinetic database of titanium-based alloys.