Multiscale Simulation Study Of The Plastic Deformation Behavior Of Nickel-Based Superalloys

Nickel-based superalloy is widely used in aviation propulsion and industrial gas turbine components with its excellent high-temperature mechanical properties.The improvement of its mechanical properties and reasonable structural design can effectively improve its working efficiency and reliability in component application.At present,most studies on its mechanical behavior focus on experiments and macroscale simulations,and there is a lack of relevant studies on the deformation mechanism of nickel-based superalloy at the micro-nanoscale.In addition,the existing classical constitutive models suitable for metal materials in the large-scale finite element simulation of superalloys lack relevant correction data.In this paper,the plastic deformation behavior and deformation mechanism of nickel-based superalloy are explored by combining molecular dynamics and finite element simulation.The tensile properties and deformation mechanism under different grain sizes(6.54～20nm),strain rate(1×10~7～5×10~8/s)and temperature(300～1000 K)were studied.The results show that,different from the plastic deformation dominated by twin in nano polycrystalline nickel,the nickel-based superalloy deformation is mainly based on the martensitic phase transition of stacking layer cubic(FCC)-dense row hexagonal(HCP).However,as with nickel,the Hall-Petch turning point is also present in the nickel-based superalloy.Strain rate sensitivity is closely related to grain size and strain rate.Grain binding is observed at lower strain rates,while grain boundary diffusion is observed at higher strain rates.Moreover,both rheological stress and Young’s modulus are strongly affected by temperature,which increases accelerates grain boundary diffusion and migration.This study illustrates the deformation mechanism of nickel-based superalloy from the atomic scale and provides theoretical guidance for the design of novel nickel-based superalloy with excellent mechanical properties.The molecular dynamics simulation was used to explore the pull-pressure asymmetry at different grain sizes(6.54～20 nm),strain rate(1×10~7～5×10~8/s)and temperature(300～1000 K).The results show that stretching and compression have similar Hall-Petch laws,and the rheological stress of compression is higher than stretching,which is due to the smaller spacing between atoms and the greater friction between atoms that makes deformation more difficult to occur.With the increase of grain size,the deformation mechanism changes from grain boundary leading to dislocation leading,leading to the maximum asymmetry of tensile and compressive strength at grain size of about 15.03 nm.The strain rate sensitivity coefficient m for compression at different rates is consistently higher than that for stretching,and the gap between pulling pressures gradually increases with increasing strain rates.Stretching promotes the formation and expansion of stacks and dislocations more than compression.As the temperature increases,the formation and development of dislocations will be hindered,and the higher the temperature,the closer the mechanism of dislocation evolution under tensile and compressive loads,resulting in the reduction of the tensile-compression asymmetry of nickel-based superalloys at higher temperatures.By the the properties of GH4169 alloy,the strength of GH4169 alloy gradually gradually.Combining stretching experiments and finite element simulations,correcting the relevant material parameters in the Johnson-Cook constitutive model shows that the modified Johnson-Cook constitutive model can predict the material stretching behavior well in the range of 20℃-650℃.