Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through microanalyses of microstructurally small cracks
Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through microanalyses of microstructurally small cracks
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DOI：
10.1016/j.actamat.2012.01.023
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发表时间：
2012-04-01
期刊：
影响因子：
9.4
通讯作者：
Noguchi, Hiroshi
中科院分区：
文献类型：
--
作者：
Takahashi, Yoshimasa;Shikama, Takahiro;Noguchi, Hiroshi
本文详细研究了沉淀硬化Al-Mg-Si合金（6061-T6）在10（7）个循环以上的高周疲劳（HCF）区的疲劳寿命控制机理。结果表明，在相对较低的应力幅下，90%以上的疲劳寿命是由微观小裂纹的扩展过程所占据的。经常发现小裂纹在再次开始生长之前被阻止和停止很长一段时间（超过106个周期），这导致显著缓慢的生长过程。小裂纹，然后分析，不仅通过传统的断口，但也通过使用聚焦离子束和透射电子显微镜的裂纹尖端区域的横截面观察。这些观察，并辅以晶粒取向分析，利用电子背散射衍射，明确揭示了以下几点：（i）在试样表面上观察到的小裂纹扩展主要与只发生在试样表面的小平面型裂纹有关;（ii）小裂纹的扩展方向具有很强的各向异性（即表面诱导生长）;（iii）的小面型裂纹是与形成持久的细滑移带，伴随着没有结构变化的矩阵。在此基础上，详细讨论了HCF区小裂纹扩展的微观机制及其与疲劳极限概念的关系。(C)2012 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
The mechanism controlling the fatigue life of a precipitation-hardened Al-Mg-Si alloy (6061-T6) at a high-cycle fatigue (HCF) regime of over 10(7) cycles was investigated in detail. It was found that over 90% of the total fatigue life was occupied by the growth process of a microstructurally small crack at relatively low stress amplitude. The small crack was often found to be arrested and halted for a long period (more than 106 cycles) before it began to grow again, which resulted in a significantly slow growth process. The small crack was then analyzed not only by the conventional fractography but also by the cross-sectional observation of the crack tip region using a focused ion beam and transmission electron microscopy. These observations, supplemented also by a grain orientation analysis using electron backscattered diffraction, explicitly revealed the following points: (i) the small crack growth observed on the specimen surface is primarily related to facet-type cracking that occurs exclusively at the specimen surface; (ii) the growth direction of the small crack has strong anisotropy (i.e. surface-induced growth); (iii) the facet-type cracking is related to the formation of persistent fine slip bands that accompany no structural change of the matrix. On the basis of these results, the micromechanism of small crack growth and its relation to the concept of fatigue limit at the HCF regime is discussed in detail. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.