Composition Design,Microstructure And Properties Investigate Of A Novel Cobalt Base Superalloy

Co-Al-W series superalloys have attracted wide attention from researchers of hightemperature materials because of their γ’-Co3(Al,W)phase with L12 structure.Although the addition of a large amount of W element in the alloy improves the stability of the γ’phase,it also increases the density of the alloy and limits its application in the practical aviation.Therefore,replacing the W element with other alloying elements to reduce the density of the alloy and improve the stability of the alloy structure are urgent problems to be solved for cobalt-based superalloys.In this paper,the Co-Al-Ni(Cr,Ti)system was quickly established by highefficiency diffusion multi-section experiments.According to the experimental results,the element content range of the new cobalt-based superalloy with γ’+γ dual phase structure was obtained.The effects of total AI+Ti content,Al/Ti atomic ratio and the addition of Cr and Mo alloying elements on the equilibrium structure and lattice misfit of the alloy were analyzed by thermodynamic calculation software.According to the results of diffusion multi-section experiments and thermodynamic optimization calculations,a novel cobalt-based superalloy with five different compositions was designed by adding Cr and Mo alloying elements,changing the Al/Ti value and investigating the effects of alloy element content changes on the structure and properties of new cobalt-based superalloys.Diffusion multivariate experiments and thermodynamic calculation results show that the addition of Ni in the alloy stabilizes the γ’ phase.The high contents of Ti,and the addition of Cr and Mo all increase the precipitation tendency of η phase,δ phase,and μ phase in alloy.The results of microstructure study of five noval cobalt-based superalloys show that all the microstructures consist of γ’-(Co,Ni)3(Al,Ti)and γ phases.The increase of Ti content in the alloy increased the average size of γ’ phase,the volume fraction of γ’phase and the lattice misfit.The addition of Cr and Mo elements to the alloy increased the average size of the γ’ phase and the volume fraction of the γ’ phase.Due to the segregation of Cr and Mo into the y and γ’ phase,the lattice mismatch ratio of the alloy increases and decreases,respectively.The results of performance studies of five noval cobalt-based superalloys show that the densities of all alloys were lower than that of tungsten-containing alloys.As-cast alloys had lower hardness compared to aging alloys.Increasing the Ti content in the alloy can significantly increase the hardness and tensile strength of the alloy.The hardness and tensile strength of the alloys were reduced by the addition of Cr element,and were increased by the addition of Mo element.According to the change of the mechanical properties in aging alloys,it is determined that the mechanical properties of the aging alloy were determined by the γ’ phase strengthening and the lattice misfit.In addition,the hot corrosion resistance of the alloys decreased with increasing Ti content,which was significantly improved by the addition of Cr or Mo element.