| Hastelloy C-276 nickel-based superalloy is a metal material widely used in the fields of nuclear power and chemical industry.Parts prepared from this alloy material are usually produced by hot processing.However,the plastic deformation of materials in the hot working process is often uneven,and the evolution process of the internal microstructure is also relatively complex.In addition,the hot working range of the alloy is relatively narrow,so it is difficult to control the quality of the final prepared parts.Aiming at the non-uniform deformation characteristics of hot working,this paper designed a thermal compression experiment under variable conditions different from the traditional constant condition.Combining the experiment and simulation,the cellular automata model was used to simulate the dynamic recrystallization process under different conditions,and the influence of the deformation history of materials on the microstructure evolution was analyzed.Based on the two-dimensional dynamic recrystallization cellular automata,a three-dimensional cellular automata model is established in this paper.The specific research contents and conclusions are as follows:(1)The stress and strain curves of HC-276 alloy after hot compression show an obvious dynamic recrystallization softening phenomenon,and most of the stress curves still do not reach the equilibrium state at the end of compression,indicating that HC-276 alloy has an obvious dynamic recrystallization tendency during hot processing,and its hot working range is small.The microstructure study shows that the thermal processing history has great influence on the recrystallization process and evolution process.According to the experimental results,a hot working diagram based on Murthy instability criterion was drawn,and the ideal process parameters and instability interval of HC-276 alloy were determined.(2)The dynamic recrystallization cellular automata model with variable working conditions was established,and the thermal compression experiment with shifted strain rate and temperature was simulated.The reliability of the model was verified by comparing with the experimental data.The simulation results show that it is more difficult to obtain complete recrystallization microstructure in the hot compression experiment with abrupt strain rate compared with that at constant rate.Based on the simulation results of cellular automata,the hot compression process parameters of complete recrystallization under variable working conditions were designed and verified by experiments.(3)Based on the physical-metallurgical theory of recrystallization,a cellular automata program for simulating dynamic recrystallization process in three-dimensional space was constructed by extending the two-dimensional cellular automata model,which was verified by comparison with experiments.The results show that the three-dimensional cellular automata model can not only accurately predict the flow stress curve and microstructure characteristics during the thermal compression process,but also better reflect the change of recrystallization kinetics curve compared with the two-dimensional cellular automata model. |
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