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Title: Influences of granular constraints and surface effects on the heterogeneity of elastic, superelastic, and plastic responses of polycrystalline shape memory alloys

Deformation heterogeneities at the microstructural length-scale developed in polycrystalline shape memory alloys (SMAs) during superelastic loading are studied using both experiments and simulations. In situ X-ray diffraction, specifically the far-field high energy diffraction microscopy (ff-HEDM) technique, was used to non-destructively measure the grain-averaged statistics of position, crystal orientation, elastic strain tensor, and volume for hundreds of austenite grains in a superelastically loaded nickel-titanium (NiTi) SMA. These experimental data were also used to create a synthetic microstructure within a finite element model. The development of intragranular stresses were then simulated during tensile loading of the model using anisotropic elasticity. Driving forces for phase transformation and slip were calculated from these stresses. The grain-average responses of individual austenite crystals examined before and after multiple stress-induced transformation events showed that grains in the specimen interior carry more axial stress than the surface grains as the superelastic response "shakes down". Examination of the heterogeneity within individual grains showed that regions near grain boundaries exhibit larger stress variation compared to the grain interiors. As a result, this intragranular heterogeneity is more strongly driven by the constraints of neighboring grains than the initial stress state and orientation of the individual grains.
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [4] ;  [2] ;  [5]
  1. Colorado School of Mines, Golden, CO (United States); Northwestern Univ., Evanston, IL (United States)
  2. Northwestern Univ., Evanston, IL (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Confluent Medical Technologies, Fremont, CA (United States)
  5. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357; SC0010594
Accepted Manuscript
Journal Name:
Journal of the Mechanics and Physics of Solids
Additional Journal Information:
Journal Volume: 102; Journal Issue: C; Journal ID: ISSN 0022-5096
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
36 MATERIALS SCIENCE; X-ray diffraction; finite elements; microstructures; phase transformation; polycrystalline material
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1416044