Effect Of Alloying On The γ’ Phase Structure And Mechanical Propertie Of Co-8.8Al-9.8W Superalloys

Compared with traditional Ni-based superalloys,the novel Co-Al-W-based super-alloys have superior properties in terms of resistance to thermal fatigue,thermal cor-rosion and creep,and oxidation resistance.In order to study the effect of microalloying elements on the structure and mechanical properties of theγ’phase of Co-8.8Al-9.8W superalloy,the L1₂-Co₃（Al,W）structure of theγ’phase was constructed and extended into a 32-atoms supercell structure,and the six non-equivalent supercell structures were alloyed and doped with Mo,Nb,Ni,Ta and Ti atoms.The Co-8.8Al-9.8W super-alloy was also selected as the matrix with the addition of 2 at.%Mo,Nb,Ni,Ta and Ti to prepare the Co-8.8Al-9.8W-2X（X=Mo,Nb,Ni,Ta,Ti）alloy,and theγ/γ′and sec-ondary phases of the as-cast alloy and high temperature deformation were observed and analysed,and the alloy strengthening mechanisms and the factors influencing the failure mechanisms were investigated.The calculation results show that Mo atoms occupy the W₆ site most preferentially and the Co₃ site second preferentially to form theγ’phase doped structure,and their strength and hardness decrease and their structural stability decreases.Ni atoms pref-erentially occupy the Co₃ site and secondarily the Co₄ site to form theγ’phase doped structure,which decreases in strength,increases in hardness and structural stability;Ti atoms preferentially occupy the Co₃ site and secondarily the Al₂ site to form theγ’phase doped structure,which decreases in strength and hardness,but increases in struc-tural stability.Compared to the as-cast alloy,theγ’phase in the Co-8.8Al-9.8W superalloy sub-jected to 800°C/5%strain shows a slight decrease in cubicity due to slight rafting but the morphology remains sub-cubic overall;theγ’phase in the 2Mo alloy shows a de-crease in cubicity and an increase in size due to rafting and association and merging behaviour,and its morphology changes from sub-cubic to sub-cubic.Theγ’phase in the 2Nb alloy shows an increase in cubicity and size due to association and merging,and its shape changes from sub-cubic to cubic;theγ’phase in the 2Ni alloy shows a decrease in cubicity due to rafting,and its shape changes from sub-cubic to rafting;theγ’phase in the 2Ta and 2Ti alloys shows an increase in size due to association and merging and its shape remains as The shape remains highly cubic.A certain number of needle-like/lamellar secondary phases precipitate in the as-cast alloy,with an increase in the number of needle-like secondary phases in the 2Mo alloy and an increase in the number of lamellar secondary phases in the 2Ta alloy;the number of needle-like/la-mellar secondary phases is significantly reduced after high temperature deformation compared to the as-cast alloy.The strengthening mechanism of the alloy in the process of high temperature de-formation is mainlyγ/γ’two-phase channel narrowing under stress,so that the disloca-tion winding plug product forms a channel dislocation network,which hinders the mo-tion expansion of the dislocation in theγ/γ’two-phase channel;at the same time,an interface dislocation network is formed around theγ’phase,which can hinder the dis-location at the interface of theγ/γ’two-phase,so that it cannot be extended to the inside of theγ’phase to cause damage and ensure the integrity of theγ’phase.The near-cubicγ’phase is destroyed by dislocation shear due to raft deformation,the highly cubicγ’phase is destroyed by dislocation shear due to joint bonding,and the near-circular cubicγ’phase is destroyed by dislocation shear due to the joint influence of raft deformation and joint bonding.The nanoindentation hardness as well as the elastic deformation capacity of the Co-8.8Al-9.8W-2X superalloy show improvements compared to the C o-8.8Al-9.8W base superalloy,with the 2Ta and 2Nb alloys showing more nano-hardness,followed by the 2Mo alloy and finally the 2Ti and 2Ni alloys with similar nano-hardness;the alloys show no significant differences in terms of higher elastic modulus.Th e high-temperature ultimate compressive and plastic deformation capacities of several alloys,except for 2Ti alloy,showed different degrees of improvement compared to the base alloy,while the high-temperature ultimate compressive and plastic deformation capac-ities of 2Ti alloy showed a decrease;a comprehensive analysis of the stresses and strains of the alloys shows that the high-temperature deformation capacities of the al-loys,in descending order,are 2Ta,2Nb,2Mo,Co-8.8Al-9.8W,2Ni,2Ti.