材料期刊网

通过高压扭转对Cu试样施加不同程度的变形, 利用OM, TEM及差示扫描量热仪(DSC)对变形组织微观结构及其热稳定性进行了分析. 在较小的变形程度下, 变形组织为高位错密度的位错胞、亚晶组织, 试样的变形储能随变形量的增大而增大, 在切应变等于13时达到最大, 为0.91 J/mol, DSC曲线显示的放热峰随变形量的增大向低温方向偏移; 进一步变形, 动态回复加剧, 高位错密度的亚晶组织逐渐演化成无位错的等轴状晶粒组织, 试样的变形储能减小, 组织的稳定性提高. 显微硬度随退火温度的提高而减小, 晶粒的明显长大导致显微硬度急剧减小. 出现明显晶粒长大的温度较DSC曲线显示的放热峰起始温度低45℃左右, 这主要是由于变形组织的回复再结晶过程是退火温度与时间的函数,降低处理温度并延长处理时间能达到与高温短时处理相同的效果.

The thermal stability of Cu specimens subjected to high–pressure torsion (HPT) deformation with varying strains was studied by optical icroscope (OM), differential scanning calorimetry (DSC) and transmission electron microscope (TEM). It is found that cellular subgrains with high dislocation densities are firstly formed at a low strain level, some of the cellular subgrains are transformed into dislocation–free equiaxed grains at larger strains. A single exothermal peak between 150 and 250 ℃ is shown in DSC curves, corresponding to the heat release due to recrystallization and subsequent grain growth. With the increase of strain, the peak position is shifted to a lower temperature and then is leveled off, but the stored energy of cold work, calculated according to the area under a peak, increases with strain at relatively low strain level and reaches its maximum value of 0.91 J/mol at strain of 13. Further deformation induces the stored energy of cold work to decrease due to the dynamic recovery of microstructure. A large drop in hardness appears in as–deformed samples at a temperature 45 ℃ lower than the start temperature of the exothermal peak after isochronal annealing, indicating that the recrystallization and grain growth process is closely relatine to annealing time and temperatur.