高压扭转大塑性变形Al­Mg铝合金中的层错和形变孪晶

摘要

Dislocation, stacking faults (SFs) and deformation twins (DTs) in nanostructured Al­Mg alloys processed by high pressure torsion were identified using high­resolution transmission electron microscopy (HRTEM). The results show that SFs and DTs with high density exist within both nanocrystalline and ultrafine grains. SFs formed by Shockley partials can be dissociated from both 0° screw and 60° mixed dislocations. The homogeneous and heterogeneous twinning mechanisms previously predicted by molecular dynamics simulations were directly verified by HRTEM. A special four­layer twin formed by the dynamic overlapping of four SFs is experimentally observed. In addition, HRTEM observations suggest that stair­rod dislocations and Lomer­Cottrell locks form by the reactions of trailing partials of SFs meted on different slip planes. Based on the classical dislocation theory and the partial emission from grain boundaries, a new model to describe the nucleation and growth of SFs and DTs in ultrafine­grained FCC metals and alloys was proposed.%利用高分辨透射电镜研究高压扭转大塑性变形纳米结构Al­Mg铝合金中的位错、层错和形变孪晶。结果表明：在纳米晶和超细晶内均存在高密度的层错和形变孪晶；形成层错的Shockley部分位错可分别由0°纯螺型位错和60°混合位错分解得到；纳米孪晶既可由晶内层错动态叠加而形成，也可由晶界向晶内不断发射部分位错而向晶内长大，从而分别实验证实了分子动力学模拟预测的均质和非均质形核长大的孪生机制；观察到了由4层层错动态叠加而形成的特殊纳米孪晶。此外，高分辨透射电镜观察表明：在不同滑移面上的层错相交时，形成层错而产生的拖曳部分位错相遇可反应生成压杆位错和 Lomer­Cottrell 位错锁。依据经典位错理论和晶界发射部分位错的机制，提出了描述超细晶面心立方金属和合金中层错和形变孪晶形核长大的新模型。