Atomistic study on crystal orientation-dependent crack propagation and resultant microstructure anisotropy in NiTi alloys

GQ Xie and F Wang and X Lai and ZP Xu and XG Zeng, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, 250, 108320 (2023).

DOI: 10.1016/j.ijmecsci.2023.108320

The primary objective of this study was to explore the crystal orientation-dependent fracture mechanism of nickel-titanium (NiTi) alloys by using molecular dynamics simulations. We discovered that the stress concentration ahead of the crack tip induced the formation of martensite with a herringbone twin or mixed HCP/ OTHER atom morphology, while reverse martensite transformation occurred behind the crack tip due to stress relaxation. Interestingly, typical brittle fracture by cleaving along the high-energy domain boundary, quasibrittle fracture as a result of the transformation-induced plasticity, as well as ductile fracture caused by a combination of phase transition, stacking fault, and atomic slip were observed in the samples with (100) 010, (110) 110, and (112) 111 crack orientations, respectively. The findings demonstrated that the crack growth behavior in each orientation was closely correlated to the microstructure evolution around the crack tip. Moreover, the relationship between the traction force and separation was achieved from the fracture process zone near the crack surface. The reported orientation dependency of the traction-separation curves was decisively driven by the anisotropy of cracking characteristics and microstructure morphologies. The results of this work offer comprehensive insights into the importance of crystal orientations on the atomic-scale fracture performance of NiTi alloys.

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