Variant Evolution During Heating Transformation And Microstructural Evolution Of Twins Induced By Electric Current Pulses In A Cu-Zn Alloy

Up to now, there is no report about the influence of the crystallographic information on the material properties in the high temperature. As a new typical technology, Electric Current Pulses (ECP) is widely used to improve materials’microstructures and their properties. Especially, due to the rapid heating and high-rate cooling, ECP is able to maintain the unstable high temperature phase to the room temperature, and it makes the study of the microstrucutural evolution in high temperatures become possible, while which is usually limited for the traditional heat-treating process.In this work, the effects of ECP on variant evolution and twins formed in the early stages of the phase transformation and the recrystallization are investigated in a Cu-Zn alloy by the SEM-EBSD and TEM methods.By investigating the effects of the current density on variant evolution and twins formed in the early stage of phase transformation induced by ECP in a double-phase Cu-Zn alloy, the results show that the nucleation rate of β phase are greatly improved and the contents of β phase are also increased with the current density increasing. Further investigations on the α→β phase transformation indicate that orientation relationship between β phase(fcc) and β phase(bcc) obeys K-S relationship. Moreover, during α->β phase transformation, the α grains are broken by the nucleation and growth of β phase from a grains.By investigating the effects of high-rate cooling on twins and dislocation in the early stage of phase transformation induced by ECP in a double-phase Cu-Zn alloy, the results show that the cooling rate at the corner area is faster than that in the center area separated from one sampled. The faster the sample cooling rate, the more dislocation there is, so as to the content of deformation twins. In addition, it is found that deformation twins are sensitive to temperature, and they would disappear as soon as the temperature increasing.By TEM method, the evolution of the dislocation and twins in the recrystallization process induced by ECP is investigated. The results show that the contents of the dislocation and deformation twins are greatly decreased after treated by ECP. However, a lot of incomplete annealing twins are emerged. Especially, the various microstructures of annealing twins are revealed, and the different growth directions are also observed after treated by ECP.