Characterisation of short fatigue cracks in titanium alloy IMI 834 using X-ray microtomography
Characterisation of short fatigue cracks in titanium alloy IMI 834 using X-ray microtomography
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DOI：
10.1016/j.actamat.2015.07.069
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发表时间：
2015-10
期刊：
影响因子：
9.4
通讯作者：
T. Chapman;K. Kareh;M. Knop;T. Connolley;P. Lee;M. Azeem;D. Rugg;T. C. Lindley;D. Dye
中科院分区：
文献类型：
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作者：
T. Chapman;K. Kareh;M. Knop;T. Connolley;P. Lee;M. Azeem;D. Rugg;T. C. Lindley;D. Dye
首次尝试对自然产生的表面连通和内部疲劳裂纹进行三维评价。利用高温(350℃)空气和真空环境下的X射线显微层析成像技术，结合断口扫描电子显微镜，对空气和真空环境中疲劳裂纹的萌生和扩展进行了研究。在真空(<；10−5mbar)下，观察到多个内部和表面连接的裂纹萌生，但只有表面连接的裂纹扩展。相比之下，在空气中形成的裂缝较少，这些裂缝大多是表面连接的，而且都被观察到在生长。在所有情况下，起始特征都与球状初级α相关联。在真空中发现疲劳寿命提高，这主要是由于延迟起裂的结果，但也是由于疲劳裂纹扩展较慢。内部裂纹的不扩展被认为意味着，即使在这里获得的良好的实验室真空也不足以模拟部件中内部裂纹的条件。在疲劳裂纹扩展过程中，裂纹在空气中的形状演变为半圆形a/c=1，而真空裂纹保持半椭圆形(a/c≃1.4)。这意味着氧化物诱导的裂纹闭合在空气中的疲劳裂纹扩展中起到了作用。
A first attempt at the three-dimensional evaluation of naturally initiated surface connected and internal fatigue cracks is presented. Fatigue crack initiation and growth in air and vacuum environments have been investigated through X-ray microtomography in air and vacuum environments at elevated temperatures (350° C), accompanied by post-mortem electron microscopy of the fracture surfaces. In vacuum (< 10− 5 mbar), multiple internal and surface-connected crack initiation was observed, but only the surface-connected cracks grew. In contrast, fewer cracks formed in air, these were mostly surface-connected and all were observed to grow. In all instances the initiation features were associated with globular primary α. An improved fatigue life was found in vacuum, which was mostly a consequence of delayed initiation, but was also due to slower fatigue crack propagation. The non-propagation of internal cracks was taken to imply that even the good laboratory vacuum obtained here was insufficient to simulate the conditions obtained for an internal crack in a component. The crack shape evolved towards a semi-circular shape a/c= 1 in air during fatigue crack growth, whilst the vacuum cracks remained semi-elliptical (a/c≃ 1.4). This was taken to imply that oxide-induced crack closure played a role in fatigue crack growth in air.