Hot Deformation Behavior And Microstructure Evolution Of Nickel-based Superalloys During Hot Deformation

Nickel-based superalloy has an important application in aero-engine,but it has many elements and high alloying degree,and is prone to uneven microstructure,hot working crack,abnormal grain growth and other defects during hot working,which greatly affects its properties and even leads to the scrap of components.Therefore,it is very important to study the thermal deformation behavior and microstructure evolution of nickel-based superalloy during hot working to control the grain structure and properties.Based on this,this paper took A2 nickel-base powder superalloy and GH141 nickel-base superalloy as the research objects,studied their thermal deformation behavior and microstructure evolution,optimized the process parameters,and provided data support for subsequent hot forging.(1)For A2 and GH141 superalloys,the true stress-strain curves show a similar trend,namely dynamic recrystallization characteristic.The flow stress changes with the change of true strain,which is the result of the integration of work hardening effect and dynamic softening effect during deformation.Among them,work hardening is caused by dislocation multiplication and plug up.Dynamic recovery and dynamic recrystallization lead to dynamic softening effect.In the process of thermal deformation,the flow stress is obviously affected by temperature,strain rate and other factors,mainly manifested in that the flow stress will gradually decrease with the increase of thermal deformation or the decrease of strain rate.(2)The hot deformation activation energies of A2 Nickel-based powder metallurgy superalloy and GH141 Nickel-based superalloy are 536.36KJ/mol and 487.579KJ/mol,respectively.Based on the hot compression test data,the Arrhenius constitutive equation model was constructed considering temperature change correction,friction correction and strain compensation correction.For A2 Nickel-based powder metallurgy superalloy,the mean relative error(AARE)and correlation coefficient(R~2)of the model are calculated to be 9.45%and 0.98291,respectively.For GH141 Nickel-base superalloy,the mean relative error(AARE)and correlation coefficient(R~2)of the model are calculated to be 9.43%and0.97454,respectively.These indicate that indicating that the constructed constitutive equations can accurately predict the flow stress under different deformation conditions.(3)The thermal processing map based on DMM shows that the optimal thermal processing window of A2 Nickel-base powder metallurgy superalloy is as follows:the deformation temperature is 1075??1150?and the strain rate is 10^-3s^-1?10^-1.5s^-1;The optimum hot working window of GH141 Nickel-base superalloy is as follows:deformation temperature 1125??1140?,strain rate 10^-2.0s^-1?10^1.0s^-1.(4)The results of microstructure analysis show that for A2 Nickel-base powder superalloy and GH141 Nickel-base superalloy,the grain size is smaller at lower deformation temperature and higher strain rate,and gradually increases with the increase of deformation temperature and the decrease of strain rate.For GH141 Nickel-based superalloy deformed at high strain rate of 10 s^-1,the deformation time is very short,and the heat generated by the plastic deformation cannot be timely emitted,resulting in the adiabatic heating effect in the compression process,which leads to the actual temperature greater than the preset temperature,resulting in grain size increase.