Study On Hot Deformation Behavior And Hot Workability Of Nickel-based Superalloy

Nickel-based superalloys refer to alloys that have appropriate strength and excellent oxidation and thermal corrosion resistance at a temperature of 650 to 1100 ? with nickel as the matrix.Nickel-based superalloys are mainly used in aerospace,petrochemical,nuclear power,etc.However,our country's nickel resources are scarce,and the price of imported nickel is remarkably high.Therefore,the study on nickel-saving austenitic alloys has become the focus of attention.In the present work,nickel-based superalloy X-750 and nickel-saving heat-resistant alloy 253 MA were taken as research objects.Single-pass thermal compression tests of these two alloy materials under different deformation conditions were carried out on the Gleeble-3500 thermal simulation test machine.The true stress-true strain dates were analyzed,and strain coupled Arrhenius constitutive models were established.The accuracy predicted flow stress by the above model was verified;The thermal processing diagrams of the two alloys under different true strain conditions were drawn.The evolution of the microstructures was observed with the EBSD characterization technology.The feasibility of using the processing diagrams to optimize the thermal processing parameters was evaluated;Physical constitutive models based on the deformation mechanism were established for the two alloys.The relationship between the recrystallization volume fraction and the deformation characteristic parameters were discussed.The main conclusions of the present work are as follows:(1)The true stress-strain curves of the two alloys are drawn,and the flow stress curves are typical dynamic recrystallization curves.The influence of different deformation parameters on the high-temperature rheological behavior of the two alloys is analyzed: with the increase of the deformation temperature or the decrease of the strain rate,the flow stress of the alloy shows a downward trend.At the early stage of deformation,the stress increases sharply under the effect of work hardening.As strain increases,the dynamic softening mechanism inside the alloy starts,which partially offsets the work hardening effect.When the storage energy reaches the critical value,the dynamic recrystallization becomes alloy the dominant deformation mechanism.The internal grains of the material gradually transform into recrystallized equiaxed crystals.(2)Arrhenius constitutive models based on phenomenological coupling strain was established for X-750 and 253 MA alloys.The verification showed that the constitutive model can predict the alloy's high-temperature deformation behavior well.The correlation coefficient and average relative error of the constitutive equation of X-750 alloy are 0.98102 and 9.63%,respectively.The correlation coefficient and average relative error of the constitutive equation of 253 MA alloy are 0.98762 and 7.85%,respectively.(3)Physical constitutive models based on the deformation mechanism were established for the X-750 and 253 MA alloys during the hot working process at the dynamic recovery and dynamic recrystallization stages.The relationship between the dynamic recrystallization volume fraction and the deformation parameters was discussed based on the dynamic recrystallization kinetic models: as the deformation temperature increases or the strain rate decreases,the dynamic recrystallization mechanism gradually plays a more important role.(4)The thermal processing diagrams of the two alloys under different strains were drawn,and the power dissipation zone and the rheological instability zone are discussed in combination with the EBSD diagram,and the safe processing zone for the thermal processing of different alloys are determined.The influence of deformation parameters on the microstructure of the two alloys was discussed: as the increase of deformation temperature or decrease of strain rate,the size of dynamic recrystallization grains and the degree of dynamic recrystallization increase.