Fatigue and fracture of shape memory alloys in the nanoscale: An in-situ TEM study
Fatigue and fracture of shape memory alloys in the nanoscale: An in-situ TEM study
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DOI：
10.1016/j.scriptamat.2023.115577
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发表时间：
2023-05-30
影响因子：
6
通讯作者：
Sehitoglu, H.
中科院分区：
文献类型：
--
作者：
Sidharth, R.;Stinville, J. C.;Sehitoglu, H.
本研究旨在探讨奈米镍钛形状记忆合金薄膜之疲劳与断裂机制。在功能疲劳期间，永久应变归因于由Ni 4 Ti 3沉淀物和平行于马氏体的II型内部孪晶的界面位错钉扎的残余马氏体。这些残余马氏体-奥氏体界面作为应力诱发马氏体在随后的循环中的异质形核位点，从而解释了相变应力的降低。最后，观察到结构失效沿沿着富含位错的贝氏体-马氏体界面发生，使其成为微观结构中最薄弱的环节，从而在导致永久应变积累的功能疲劳机制与导致断裂的结构疲劳机制之间建立直接联系。这项工作提供了一个全面的理解纳米形状记忆合金的变形机制，并指出适用于宏观尺度的基本机制。
This study is aimed at demonstrating the fatigue and fracture mechanisms in nanoscale NiTi shape memory alloy thin films. During functional fatigue, permanent strains are attributed to residual martensite pinned by Ni4Ti3 precipitates and interfacial dislocations parallel to type II internal twins of the martensite. These residual martensite-austenite interfaces acted as heterogeneous nucleation sites for stress-induced martensite in subsequent cycles thereby explaining the reduction in transformation stress. Finally, structural failure was observed to occur along the dislocation-rich austenite-martensite interface, making it the weakest link in the microstructure thus establishing a direct link between mechanisms of functional fatigue that result in the accumulation of permenant strain and mechanisms of structural fatigue that result in fracture. This work provides a comprehensive understanding of deformation mechanisms in nanoscale shape memory alloys and points to fundamental mechanisms that are applicable to macro scales.