The Optimization Mechanism Of The Grain Boundary Character Distribution In Pure Copper Under Low-strain Level

Nowadays,grain boundary engineering has become an effective method to solve grain boundary-related failure of materials and a valuable mean to enhance properties.The theoretical requirements of evolutionary process in grain boundary engineering is gradually raising with more and more practical application.Therefore,this paper,by means of electron back scatter diffraction(EBSD),was designed to investigate the synthetic effect of pre-deformation and annealing temperature on grain boundary character distribution in pure copper and related microstructural evolution during thermomechanical process treatments.Meanwhile,quasi situ EBSD observation was used to explore optimized mechanism and evolution of grain boundaries during thermomechanical process.The relationship among grain boundary character distribution,level of pre deformation and annealing temperature has been researched in GBE process in polycrystalline copper.Under the same level of pre deformation,low ?CSL boundaries will increase with lifting annealing temperature.And fraction of special boundaries rises firstly then descends later with increasing deformation while annealing temperature is constant.The only abnormal sample occurs in 700?-10%.In addition,the optimized GBCD can be obtained under 10% pre deformation and annealing at 600?,in which the proportion of special boundaries reaches 81.70%.Behaviors of microstructure evolution have been confirmed in different thermomechanical treatment by analyzing grain size and local misorientation.Recovery takes the lead under 5% compression till it is replaced by SIBM when annealing temperature goes up to 700?.Similarly,SIBM mainly occurs in 10% compression samples and the behavior converts to recrystallization when anneal at 700?.Then,recrystallization is dominant in all 15% samples.It is obvious that SIBM will turn to recrystallization when enough stored energy and thermal activation energy are provided.Furthermore,SIBM is more effective to optimize GBCD,which may result from high velocity of boundary migration.The effect of different microstructure evolution on GBCD optimization has been discussed via quasi situ observation.Recovery has little effect on optimization due to a small range of interaction and migration.While in SIBM,notable boundary migration is prevalent to produce abundant twins and interactions to get the GBCD optimized,which is stimulated preferentially in the highest energy region,then proliferate further to other high energy region step by step instead of proceeding simultaneously.With consumption of stored energy and migration of boundaries,the GBCD is gradually optimized.Then during recrystallization,new formation of grain and their primary growth may be the key to this optimized behavior.But as a large quantity of energy is consumed in an extremely short period in these two procedures,they can just partly contribute to optimization and the velocity of boundary migration in later stage becomes slower,which leads to less effect in optimization in recrystallization.