Cellular Automaton Modeling Of Microstructural Evolution In Nimonic 80A Superalloy During Hot Deformation

Nimonic 80 A is a typical nickel-base superalloy,and is generally used to manufacture turbine blade,gas turbine,bolt and bushing.It can work steadily under elevated temperature circumstance due to the superior strength and resistance of creep,oxidant and corrosion.In addition,due to the high-temperature strength,processing of Nimonic 80 A is complicated and difficult.During hot deformation of metallic materials,there will exist various mechanisms,including work hardening(WH),dynamic recovery(DRV),dynamic recrystallization(DRX),static recovery(SRV),static recrystallization(SRX)and metadynamic recrystallization(MDRX).These deformation mechanisms have an important influence on the microstructural evolution during material deformation.Therefore,in order to reasonably control the final properties of the material,it is very important to research the thermal procedure.However,in the actual process,the micro-mechanism inside the material is difficult to directly observe,and the quantitative study of microstructure has remained in the theoretical formula.The formation of Computational Material Science(CMS)solves this problem effectively.Combined with the numerical calculation,CMS can predict and guide the actual process,and then a large amount of experimental costs and manpower and material resources can be saved.In this paper,the microstructural evolution of Nimonic 80 A superalloy during single-pass and double-pass deformation was modeled by cellular automaton(CA),and the grain growth,the DRX and the SRX behaviors were simulated.The main research contents and conclusions are as follows:1.Based on thermal activation mechanism,curvature driving mechanism and energy minimum principle,a CA model for the grain growth process of Nimonic 80 A superalloy was established.The grain growth behaviors of materials at different holding temperatures and different holding times were studied.A series of Gleeble-1500 vacuum heating experiments were performed.The experimental results confirmed that the established CA model can effectively reproduce the grain growth phenomenon of Nimonic 80 A superalloy.As the time step increases,the grain size gradually increases,the number of grains decreases,the grain boundary of austenite becomes flat and smooth,and the final grain tends to be regular hexagon.And there is no abnormal growth in the process of grain growth.The grain growth model fits the Sellars model.2.Based on the physical metallurgy principle of the dislocation density evolution during the hot deformation process of Nimonic 80 A superalloy,the CA model of DRX process was established.In the model,the variation formula of dislocation density during WH and DRV,the formula of nucleation rate of DRX and the rate of recrystallization grain growth are given in detail.The dislocation density model at the front of recrystallization is also discussed in detail.A series of Gleeble-1500 single-pass hot compression experiments were performed.The experimental results confirmed that the established CA model can effectively reproduce the DRX phenomenon of Nimonic 80 A superalloy under different deformation conditions.The results show that the hot deformation behaviors of Nimonic 80 A superalloy is affected by temperature and strain rate.As the temperature increases,both the average grain size and the fraction of recrystallized grains increase.With the increasing strain rate,the average grain size and fraction of recrystallization decreased.3.Based on the deformation mechanism of Nimonic 80 A superalloy during hot deformation and deformation gap,the CA model of SRX process was established.The formula of dislocation density evolution during SRV,the formula of incubation period,the formula of nucleation rate and the grain growth are given in the model.A series of Gleeble-1500 double-pass thermal compression experiments were performed.The experimental results confirmed that the established CA model can effectively reproduce the SRX phenomenon of Nimonic 80 A superalloy.The microstructural evolution during the deformation gap are affected by factors such as the interval time,deformation temperature,prestrain,strain rate and initial austenite grain size.The interval time and temperature play a major role.As the gap time increases,the recrystallization fraction and grain size increase.With the increasing temperature,the recrystallization fraction and grain size increase,and the SRV effect also increases.4.Based on the deformation mechanisms during two-pass hot deformation and the intrinsic difference between SRX and MDRX,the CA model of MDRX was established.During the first deformation,there were the mechanisms of WH,DRV,the nucleation and grain growth of new nuclei.During the interval,the nuclei grew subsequently and there was no new grain emerged.During the second deformation,there were the mechanisms of WH,DRV.And the MDRX grain will grow.The results of a series of Gleeble-1500 two-pass thermal compression experiments showed that the established CA model can effectively reproduce the MDRX phenomenon of Nimonic 80 A superalloy under different deformation conditions.