Theoritical Investigations Of Phase Stability,mechanical And Thermodynamic Properties Of ?' Phase In Co-Ta-X Based Superalloys

In the aerospace industry,Ni-based superalloys are the most widely used high-temperature materials and their excellent high-temperature mechanical properties are closely related to the ?/?' two-phase structure in the alloy.However,due to the melting point limitation,Ni-based superalloys are difficult to meet the requirements of further development of the aerospace industry.The discovery of a new y'-strengthened Co-based superalloy opens up new ideas for the development of next-generation superalloys.A metastable ?' phase exists in the Co-Ta-base binary alloy.Therefore,theoretically studying the effects of doping elements on the structural stability of ?'phases in Co-Ta-X based superalloys is meaningful.Based on the density functional theory,this study will use the first-principles calculation to investigate the effects of the alloying elements on the structural stability,mechanical and thermodynamic properties of Co-Ta-based and Co-Ta-Al-based superalloys were studied.The specific contents are summarized as follows:(1)The occupational tendency of traces of alloying elements X(X:Ru5 Rh,Pd,Re,Ir and Pt)in L12 and DO19 structure Co3Ta compounds are investigated.The effect of the alloying element X on the structural stability,elastic properties and thermodynamic properties of ?'-Co3Ta compounds at finite temperatures were investigated.The results show that the addition of Ru,Rh and Re can improve the relative structural stability of L12-Co3Ta compound compared with D019-Co3Ta in the temperature range of 0-1600 K.In particular,after a small amount of Re was added,the stabilization temperature range of the L12-Co3Ta compound was increased by nearly 300 K.The addition of Re increases the sensitivity of the volumetric thermal expansion coefficient of the L12-Co3Ta compound to temperature.(2)Study the occupational tendency of alloying elements X(X:Ru,Rh,Pd,Re,Ir and Pt)at different concentrations in Co3Ta compounds,and analyze the effects of concentration of alloying elements on structural stability,elastic and thermodynamic properties of ?'-Co3(Ta,X)phase at finite temperature are calculated and analyzed.The results show that the concentration of alloying elements controlled at 6.25%to 9.375%is most beneficial to improve the relative structural stability of L12.(3)Calculate the occupational tendency of alloying elements X(X:V,Ti,Ni and Cr)in Co3(Ta,Al)of L12 structure and D019 structure,and analyze effect of element X on the structural stability,elastic and thermodynamic properties of ?'-Co3(Ta,Al)phase was studied.The results show that V,Ti and Ni can improve the relative structural stability of ?'-Co3(Ta,Al)phase,especially Ni.V,Ti,Ni and Cr increase the sensitivity of the mechanical and thermodynamic properties of L12-Co3(Ta,Al)compounds to temperature,especially Cr,in the temperature range of 0 to 1600K.