Investigation On Phase Equilibria Of The Partial Cobalt-based Ternary Systems

Co-based superalloys are widely used in areas where the service life of alloy and thermal fatigue resistant are required,such as:aerospace,power,chemical and other industrial field,due to their higher initial melting temperature,excellent high temperature strength,heat-resistant corrosion,wear-resistant and organization stability.With the rapid development of science and technology,alloys’ working environment is more and more complex,it is a challenge for the development of superalloys.Further improvements in temperature capability are now being actively sought,and alloying is considered to be an effective way to solve this problem.Some of elements with high melt temperature and big atomic radius,such as Ni,Nb,Ta,W will increase the high temperature strength of Co-based alloy and its comprehensive performance.But alloying elements added can lead to the format of the TCP phase,which will decrease thermal fatigue resistance,plasticity,oxidation resistance of alloys.Therefore,the present works intend to draw the equilibria phase diagrams of some Co-base alloys.The obtained data will be contributed to thermodynamic assessment of the Co-base superalloys and the design of the related material.The results are as follows:(1)Experimental investigation of phase equilibria in the Co-Ti-Ta(1000 ℃,1100 ℃,1200 ℃)ternary system was studied.The results show that:no new ternary compound was found in this system;Ta has a vast solubility in CoTi.(2)Five isothermal sections,including the isothermal sections Co-rich of Co-V-Si(800 ℃ and 1000 ℃),Co-V-Ga(1000℃)and Co-V-Ge(800 ℃ and 1200 ℃)were determined.The results show that:The V solubility in(αCo)increased with the increase of the temperature;All of Co-V-Ga,Co-V-Si and Co-V-Ge are exist Co2VX(X=Ga,Si,Ge)phase.(3)Experimental investigation of phase equilibria in the Ni-Nb-V(1000 ℃,1200 ℃)ternary system was studied.A ternary compound τ phase with a vast homogeneity region was found.