Thermodynamic Calculation Of Nb-Ti-Co Alloy Phase Diagram And Study On Directional Solidification Behavior

In recent years,with the continuous increase in the demand for energy and smart equipment,the corresponding performance requirements for the materials required by the equipment are also increasing,which poses a challenge to the traditional casting process.Under this background,the directional solidification technology has gradually accracted people's attention.In addition,with the development of aerospace,the performance requirements for superalloys are getting higher and higher.Ti-based and Co-based alloys are widely used in the aerospace and electronics industries because of their good high temperature resistance,corrosion resistance and magnetic properties.In other industries,adding an appropriate amount of Nb alloy to the above two alloys can also form ternary Nb-Ti-Co alloys for special purposes,such as hydrogen permeation alloys and shape memory alloys.However,there are few literature reports on the complete phase diagram of the ternary alloy system and the study of the directional solidification structure transformation law,and it is urgent to study.Therefore,this paper selects the Nb-Ti-Co ternary alloy system,firstly we carries out the phase diagram thermodynamic calculation research work,then optimizes the alloy composition and combines the directional solidification process to study the microstructure evolution law,and finally we explores the effect of the Ti/Co ratio on the alloy The effect of solidification path,microstructure and hydrogen permeation performance have been all studied.Finally:we start with the phase diagram(CALPHAD)thermodynamic calculation software,combined with SEM,SRD,hardness test and hydrogen permeation experiment and other methods to conduct detailed research on its phase diagram,microstructure evolution,solidification path and hydrogen transmission performance,etc.The research contents are as follows:1.The Nb-rich angle phase diagram of the Nb-Ti-Co ternary alloy was constructed using Thermo-Calc software,and important information such as the ternary four-phase equilibrium reaction in the phase diagram was obtained,and a unified micro-segregation model was proposed.Finally,XRD and SEM were adopted.Other experimental methods verified the calculation results of the phase diagram and proved the existence of eutectic points,which enriched the solidification model of the Nb-Ti-Co ternary phase diagram.2.Research on the directional solidification behavior of the Nb-Ti-Co alloy system,focusing on the influence of alloy composition and different drawing rates on the alloy structure and solidification path.Mainly analyze the influence of different drawing rates on the microstructure of each part of the directionally solidified alloy and the evolution of the directionally solidified structure.The research results show that with the increase of the drawing rate,the distance between the peritectic and eutectic gradually decreases,and the hardness also increases,indicating that the directional solidification has a significant effect on the refinement of the structure and increases the hardness of the alloy.3.Study the effect of Ti/Co ratio on the solidification path and hydrogen permeability of Nb-Ti-Co alloy.The results show that the Ti/Co ratio has a significant effect on the solidification direction but has little effect on the solidification structure.As the Ti/Co ratio decreases,the volume fraction of the primary BCC-Nb phase decreases,while the eutectic phase increases.With these changes,the?value gradually increases.This is closely related to hydrogen diffusion coefficient and hydrogen absorption energy.Generally,the?value of Nb₄₅Ti₂₅Co₃₀alloy is 1.03(?1.08)times that of Nb₄₅Ti_27.5Co_27.5(Nb₄₅Ti₃₀Co₂₅).This can be attributed to the reduction of the hydrogen diffusion activation barrier and the smaller hydrogen adsorption energy.This work proves that the Nb-Ti-Co multiphase alloy with higher?value can still be obtained by appropriately optimizing the alloy composition,such as the Ti/Co ratio.