Kwan Charles C F, Wang Zhirui
Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada.
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clearwater Bay, Hong Kong, China.
Materials (Basel). 2013 Aug 13;6(8):3469-3481. doi: 10.3390/ma6083469.
Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors that govern the cyclic deformation mechanism(s). This study aims to advance the understanding of the cyclic deformation behavior of ufg metals through the systematic investigation of ARB processed aluminum upon cyclic loading. It was found that the cyclic softening response often reported for ufg metals is largely influenced by the microstructure stability as the cyclic softening response is facilitated by grain coarsening which becomes inhibited with highly stable microstructure. On one hand, shear bands resembling braids of dislocations trespassing multiple grains have been observed to operate for the accommodation of the imposed cyclic strain in cases where grain coarsening is largely restricted. On the other hand, it was found that the microstructure stability can be overcome at higher applied cyclic plastic strain levels, leading to grain coarsening and thus a cyclic softening response. The findings in this study have further confirmed that the cyclic softening behavior found in many ufg metals, which may be detrimental in practical applications, can be inhibited by improvements in the microstructure stability.
累积轧制复合（ARB）是最近开发的能够生产块状超细晶粒（ufg）金属的技术之一。超细晶粒金属的行为仍有许多方面缺乏深入了解，例如对控制循环变形机制的因素的普遍认识。本研究旨在通过对累积轧制复合处理的铝在循环加载下的系统研究，加深对超细晶粒金属循环变形行为的理解。研究发现，超细晶粒金属中经常报道的循环软化响应在很大程度上受微观结构稳定性的影响，因为循环软化响应是由晶粒粗化促进的，而高度稳定的微观结构会抑制晶粒粗化。一方面，在晶粒粗化受到很大限制的情况下，观察到类似位错辫子穿过多个晶粒的剪切带用于适应施加的循环应变。另一方面，发现在较高的循环塑性应变水平下可以克服微观结构稳定性，导致晶粒粗化，从而产生循环软化响应。本研究的结果进一步证实，许多超细晶粒金属中发现的循环软化行为在实际应用中可能是有害的，可以通过改善微观结构稳定性来抑制。
