The Influence Of Low-strain And Long-term Thermomechanical Treatment On The Grain Boundary Character Distribution Of Pure Copper And Related Mechanism

Nowadays,grain boundary engineering has achieved obvious progress in solving various failure problems of materials.However,people have explored the processing parameters of grain boundary engineering through experience or practice.For the parameters of thermalmechanical treatment,the impact of the optimized process on the grain boundary character distribution(GBCD)is unclear.In this paper,pure copper is selected as the model material,and low strain combined with low-temperature annealing process suitable for industrial applications was investigated.The effects of annealing temperature,deformation and annealing time on the GBCD and microstructure change behavior of pure copper were studied.The quasi-in-situ EBSD technology was used to study the grain boundary evolution law under different deformation heat treatment processes,and to explore the optimization mechanism of GBCD in the small deformation low-temperature long-term heat treatment grain boundary engineering process.Static metallographic and EBSD research,it was found that the grain boundary feature distribution in pure copper could be effectively optimized by one-step small deformation with low-temperature and long-term annealing grain boundary engineering.Among them,after annealing at 350°C for 72 h with deformation of 5%,the special grain boundary ratio reached a maximum value of 84%.The corrosion resistance of the samples processed by grain boundary engineering has been significantly improved.In the one-step small deformation with lowtemperature and long-term annealing grain boundary engineering process,the lower deformation and temperature,and the time of optimizing the grain boundary character distribution would be longer.Different deformation forces and annealing temperatures provided different driving forces and the microstructure changes during annealing.When the deformation was 5%,the strain-driven boundary migration occurred,and when the deformation was more than 10%,the obvious recrystallization behavior occurred.The evolution of the grain boundary structure during the grain boundary engineering process was tracked by quasi in situ heating metallography and EBSD.It was found that the strain-induced boundary migration or recrystallization phenomenon would destroy the original grain boundary structure.And the strain-induced boundary migration mainly occurred in the regions with higher deformation storage energy.