| Superalloy is one of the main materials used in aero-engine turbine blades.By far,the working temperature of commercial-used Ni-base superalloy is close to its melting point so that it is difficult to improve its temperature bearing capacity.Therefore,the development of a new generation of superalloys with higher temperature bearing capacity is the key problem to be solved at present.In 2006,Sato et al.discovered theγ’ phase reinforced Co-Al-W-based superalloy,which is considered as a much more potential superalloy because of its high melting point and superior high-temperature strength.However,the low γ’ phase stability and high density of Co-Al-W-based superalloys restrict the industrial application the alloy of this class.Therefore,the development of a novel low density Co-based superalloys strengthened by stable γ’phase has attracted much attention.In recent years,our group have discovered stableγ’-Co3(V,Al)and γ’-Co3(V,Ti)phases in Co-V-Al and Co-V-Ti ternary systems,respectively.In addition,this kind of alloy has low density and good mechanical properties at high temperature,which exhibit very good potential to develop lowdensity Co-based superalloys.Therefore,in this study,the study on the composition design,microstructure control and mechanical properties of Co-V-Al-based superalloys was carried out.Meanwhile,the effects of alloying elements on the microstructure,γ’solvus temperature and mechanical properties of Co-V-Ti-based superalloys were studied.The main findings of this study are as follows:(1)Based on the combination of machine learning and experimental phase diagrams,the composition design of the Co-V-Al ternary alloy was carried out to prepare Co-17V-2Al(at.%)alloy.The composition design of Co-(17-x)V-2Al-xTi serials alloys was carried out based on the method of phase diagram calculation,and the effect of Ti content on the microstructure,γ’ solvus temperature and mechanical properties of Co-V-Al-Ti alloy was studied.The research results show that the addition of Ti element significantly increases γ’ solvus temperature and mechanical properties of the Co-V-Al-based alloys,and reduces the density of the alloy.Among them,the Co11 V-2Al-6Ti(at.%)alloy has a higher γ’ solvus temperature(1098℃),a lower density(8.11 g/cm3)and good mechanical properties.(2)This study carried out a series of studies on the influence of the content of Ni,Al and V elements on the microstructure,γ’ solvus temperature and γ/γ’ two-phase composition interval of Co-Ni-V-Al-Ti alloys.The research results show that the addition of Ni element significantly increases γ’ solvus temperature of the Co-Ni-V-AlTi alloys,and expands the γ/γ’ two-phase composition range of the alloys.In addition,this study designed and prepared Co-30Ni-3V-10Al-6Ti-2Ta(at.%)alloy with a γ/γ’two-phase structure.The alloy has a high γ’ solvus temperature(1234℃),low density(8.15 g/cm3),and excellent mechanical properties.(3)This research carried out a series studies of the effect of the alloying elements Al,Mo,Nb or Ta on the microstructure,γ’ solvus temperature and mechanical properties of Co-10V-4Ti-2W(at.%)alloy.The research results show that the addition of Al,Mo,Nb and Ta elements all increase the γ’ solvus temperature and room temperature hardness of the Co-10V-4Ti-2W(at.%)alloy.Among them,Co-10V-4Ti-2W-2Ta(at.%)alloy has a higher γ’ solvus temperature(1131 ℃),a lower density(8.77 g/cm3),and a lower γ/γ’ two-phase mismatch(+0.33%),low γ’ phase coarsening rate(0.12× 10-27 m/s)and excellent mechanical properties. |
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