The Research Of Grain Boundary Engineering Of Copper Assisted By ECAP

Corrosion is the main reason of failure of metal materials, grain boundary engineering (GBE) based on thermomechanical processing (TMP) can improve the corrosion resistance of materials. Industrial pure copper (99.97%), a typical face-centered cubic metal, is used in this paper, microstructure and grain boundary character distribution (GBCD) are modified through equal channel angular pressing (ECAP) and followed by annealing treatment at a higher temperature. OM (Optical Microscopy), SEM (Scanning Electron Microscopy) and EBSD (Electron Back Scatter Diffraction) were used to investigate the microstructure and properties of pure copper which through ECAP, cold rolling, annealing treatment. the feasibility of grain boundary engineering in use of ECAP was preliminary assessed. The main results are as follows:(1) ECAP can introduce more strain than cold rolling in materials and grain refinement effect is more obvious. After 4 passes of ECAP, the average grain size is about 1μm and the hardness of copper can be up to 160HV, while after 90% cold rolled the hardness of copper is about 125HV. However, on the other hand, ECAP and large deformation of cold-rolled copper will reduce the corrosion resistance.(2) Equal channel angular pressing followed by annealing treatment could modify the microstructure and grain boundary character distribution of copper, comprehensive use of ECAP, annealing temperature and annealing time could led to form a great amount of special CSL boundaries especially the fraction ofΣ3n related boundaries. The intergranular corrosion resistance of the specimens were improved remarkably compared with the based materials.(3) The electrochemical test results indicate that the sample which through 1 pass of ECAP and annealed 2min under 860℃has the best anti-corrosion effect, EBSD results show that a large number of annealing twins have generated in its interior which interrupt the large angle grain boundary network connectivity and the proportion of special grain boundaries up to 72.5%, it is shown that the grain boundary character distribution is optimized and ECAP can be used in the grain boundary engineering. However, it should be noted that the fraction of total CSL boundaries of specimen annealed for 5min is lower than that of the 2min-annealing specimen, which resulted in the poor intergranular corrosion resistance, which is shown that long time annealing was not beneficial for formation of annealing twins.