Strain and texture evolution during mechanical loading of a crack tip in martensitic shape-memory NiTi.
In situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shape-memory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of NiTi. Upon subsequent application of a static tensile stresses, the highly textured zone reappears and grows around the crack tip as the applied stress is increased. At the highest applied stress intensity of 35MPam1/2, large tensile strains are measured ahead of the crack tip and considerable elastic anisotropy is observed. This detwinning zone is similar to the plastic zone produced by dislocation slip present around cracks in other metals. The texture in this zone is not significantly altered after mechanical unloading, despite the development of substantial triaxial compressive residual strains in this zone.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); Natural Sciences and Engineering Research of Canada
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 914987
- Report Number(s):
- ANL/XSD/JA-58892; ACMAFD; TRN: US0804866
- Journal Information:
- Acta Materialia, Vol. 55, Issue 11 ; Jun. 2007; ISSN 1359-6454
- Country of Publication:
- United States
- Language:
- ENGLISH
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