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利用透射电镜(TEM)和高分辨透射电镜(HRTEM)研究高压扭转大塑性变形纳米结构Al-Mg合金的微观结构演变和位错组态。结果表明:对尺寸小于100 nm的晶粒,晶内无位错,其晶界清晰平直;而尺寸大于200 nm的大晶粒通常由几个亚晶或位错胞结构组成,其局部位错密度高达1017 m-2。这些位错是1/2?110?型60°位错,且往往以位错偶和位错环的形式出现。在高压扭转Al-Mg合金的超细晶晶粒中,用HRTEM同时观察到分别由0°纯螺型位错和60°混合位错分解产生的Shockley部分位错而形成的微孪晶和层错。这些直接证据证实,通常存在于FCC纳米晶中由晶界发射部分位错而产生孪晶和层错的变形机制,同样可以存在于超细晶FCC金属中。基于实验结果,分析了高压扭转Al-Mg合金中的局部高密度位错、位错胞、非平衡晶界、层错和孪晶等对晶粒细化的作用,提出了相应的晶粒细化机制。
The microstructure evolution and dislocation configuration of high pressure torsion plastic deformation nanostructured Al-Mg alloy were investigated by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The results show that there is no dislocation in the grain and the grain boundaries are clear and straight for the grain size less than 100 nm. The large grains with the size larger than 200 nm usually consist of several subgrain or dislocation cell structures, Fault density up to 1017 m-2. These dislocations are 1/2? 110? Type 60 ° dislocations, and often appear in the form of dislocation pairs and dislocation loops. In the ultrafine-grained grains of high-voltage twisted Al-Mg alloy, micro-twins and layers formed by Shockley partial dislocations generated by 0 ° pure screw dislocations and 60 ° mixed dislocations respectively were simultaneously observed with HRTEM wrong. These direct evidences demonstrate that the deformation mechanisms commonly found in FCC nanocrystals that generate twins and stacking faults by partial dislocations at the grain boundaries can also exist in the ultrafine grained FCC metal. Based on the experimental results, the effect of local high-density dislocations, dislocation cells, unbalanced grain boundaries, stacking faults and twins on the grain refinement in high-pressure twisted Al-Mg alloys was analyzed. The corresponding grain refinement was proposed Mechanisms.