Coupling Effects Of Mo And Re On The Solidification Structure And Relative Phase Equilibrium Of Nickel-based Superalloy

Nickel-based superalloy has been widely used in aerospace field for its excellent high temperature comprehensive performance.The addition of Mo and Re can improve the high temperature capacity of the alloy,but also lead to the precipitation of topologicallly close-packed phase（TCP）and reduce the creep tupture life of the alloy.In this paper,the solidification microstructure and phase equilibrium of nickel-based superalloys with different Mo and Re contents were studied.The main results are as follows:The calculation results show that at 1150℃only P phase exists in the alloy when Mo content is 3.5-4.5 wt.%and Re content is 5.5-4.5 wt.%.When Mo content is 5wt.%and Re content is 4 wt.%,both P phase andμphase exist in the alloy.When Mo content is 5.5-6 wt.%and Re content is 3.5-3 wt.%,onlyμphase exists in the alloy.When Mo content is 6.5-8.5 wt.%and Re content is 2.5-0.5 wt.%,there is no TCP phase in the alloy.There are a lot ofγ/γ′eutectic in the as-cast microstructure of the alloy,and TCP phase precipitates in the alloy when Mo content is 8.5 wt.%and Re content is 0.5 wt.%.For the alloy solidified at the cooling rate of 1℃/min,when Mo content is 3.5-4.5 wt.%and Re content is 5.5-4.5 wt.%,TCP phase with P/μcoexistence precipitates in the alloy.when Mo content is 5-5.5 wt.%and Re content is 4-3.5 wt.%,no TCP phase is found in the alloy.When Mo content is 6.5 wt.%and Re content is 2.5 wt.%,TCP phase with P/μcoexistence is precipitated in the alloy.When Mo content is 7.5-8.5 wt.%and Re content is 1.5-0.5 wt.%,TCP phase andμphase with P/μcoexistence are precipitated in the alloy.For the alloy solidified at 10℃/min,when Mo content is 3.5 wt.%and Re content is 5.5 wt.%,no TCP phase is found in the alloy.With the increase of Mo content and the decrease of Re content,TCP phase with P/μcoexistence is precipitated in the alloy.Theγ′phase size of the alloy solidified at 10℃/min is nearly twice smaller than that of the alloy solidified at 1℃/min,and more TCP phase is precipitated.It is found that there are eight three-phase regions in the 1150℃isothermal section of the Al-Mo-Ni ternary system.Two three-phase regions,Al₈Mo₃+Al Mo₃+Al Ni and Al Mo₃+（Mo）+Al Ni,are determined by experiments.A total of 15 three-phase regions were identified in the 1150℃isothermal cross section of the Al-Mo-Re termite system.Four three-phase regions were identified,Al₈Mo₃+Τ1+Al₁₁Re₄、Al₈Mo₃+Al Mo₃+Τ1、（Mo）+Τ2+Τ1 andχ+（Re）+Τ2.A total of 16 three-phase regions are identified in the 900℃isothermal cross section of the Al-Mo-Re ternational system.Four three-phase regions are identified,Al₈Mo₃+Al Mo₃+Τ1、Al₈Mo₃+Τ1+Al₁₁Re₄、L-Al+Al₈Mo₃+Al₁₁Re₄ andχ+（Re）+Al Re.Two new ternary compounds,Τ1 andΤ2,have been found in the study of al-Mo-Re system.