Experimental Research And Numerical Simulation On Thermomechanical Treatment Behavior Of Ni-Co-Cr-based PM Superalloy

As the preferred material of advanced aeroengine turbine disk,nickel-based powder superalloy has excellent high temperature performance.This paper takes the hot extruded-annealed Ni-Co-Cr-based powder metallurgy（PM）superalloy as the research object.Combined with the design and preparation of high-throughput samples,finite element numerical simulation and microstructure characterization methods,the thermomechanical treatment behavior of Ni-Co-Cr-based PM superalloys was systematically investigated based on the isothermal compression experiment.The thermal deformation constitutive equation and microstructure evolution model of the alloy were established,respectively.The microstructure evolution law of the alloy during hot deformation and subsequent heat preservation was analyzed,and the mechanisms of dynamic recrystallization（DRX）and post dynamic recrystallization（PDRX）were discussed.Zener-Hollomon（Z）parameter values under different deformation conditions were calculated,and the typical Z parameter conditions were selected.The effects of key thermal deformation conditions（Z parameters and strains）and solution treatment temperature on the microstructure of the alloy were efficiently studied based on high-throughput specimens.The mapping relationship between thermomechanical treatment conditions and alloy microstructure was established.The research indicates that the material constants of the hot deformation constitutive equation of the Ni-Co-Cr-based PM superalloy in the hot extruded-annealed state are:α=0.0039,n=4.4546,A=2.8475×10⁴²,Q=1131.4 k J/mol.As the deformation temperature raises,the strain rate decreases and the amount of deformation increases.Meanwhile,the degree of DRX of the alloy gradually increases with the increasing temperature,and the dissolution of theγ’phase is also promoted.DDRX is the main DRX nucleation mechanism.The numerical simulation results of thermal deformation agree well with the experimental data,which verifies that the constructed model can effectively predict the evolution of the grain microstructure of the alloy.The PDRX kinetics of the hot extruded-annealed Ni-Co-Cr-based PM superalloy mainly depends on the deformation parameters（strain rate,temperature,deformation degree and holding time after deformation）.Increasing the deformation temperature and strain amount or extending the holding time will accelerate the occurrence of PDRX,resulting in the effective release of residual deformation energy storage.Various PDRX mechanisms exist in the alloy during post-deformation holding,including meta-dynamic recrystallization（MDRX）and static recrystallization（SRX）,as well as undissolvedγ′phase or twin-assisted nucleation.The evolution trend of the twin boundary（Σ3）during PDRX is consistent with that of the degree of recrystallization.TheΣ3 grain boundary can induce the nucleation of recrystallization so as to promote the release of energy storage.The residualγ′phase would stimulate the nucleation through dislocation pinning and accumulation during PDRX.After superslovus heat treatment on the hot deformed Ni-Co-Cr-based PM superalloy high-throughput samples,the deformed samples with low Z parameters and low effective strain（0.66≤?_e≤0.88）or high Z parameter and high effective strain（1.10≤?_e≤2.20）conditions appear abnormally large grains（ALGs）due to the uneven release of deformation energy storage.And the deformed microstructures corresponding to the regions where exhibit ALGs have lower twin density.At the temperatures of sub-solution treatment,there are obvious SRX nucleation and growth in the samples with high Z parameter and high effective strain（1.98≤?_e≤2.20）conditions.The grain microstructure under different Z parameters is gradually coarsened with the increase of solution treatment temperature and the decrease of effective strain.