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Title: In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. In this paper, we characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented by electron microscopy. We simulated the local stress state in the specimen using a microstructural model informed by the experimental data. Using these combined microstructure, deformation, and stress data, we report three phenomena, and relate them to specific sources of constraint. During initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of martensite habit plane variants that produce less than theoretical maximum transformation strain. Large Ni 4Ti 3 precipitates potentially contributed to the poor transformation response. Under load, proportional gradients in local rotation and elastic stretch developed in the martensite phase, because ofmore » the constraint at phase interfaces. Finally, this combined ff-HEDM, electron microscopy, microstructural simulation toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in other alloys with hierarchical microstructure.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [6] ;  [2] ;  [3]
  1. Colorado School of Mines, Golden, CO (United States). Mechanical Engineering; Northwestern Univ., Evanston, IL (United States). Mechanical Engineering
  2. Northwestern Univ., Evanston, IL (United States). Mechanical Engineering
  3. Colorado School of Mines, Golden, CO (United States). Mechanical Engineering
  4. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source
  5. Cornell Univ., Ithaca, NY (United States). Cornell High Energy Synchrotron Source
  6. Siberian Physical Technical Inst., Tomsk (Russian Federation)
Publication Date:
Grant/Contract Number:
AC02-06CH11357; SC0010594; 1454668; ACI-1053575; ECCS-1542205; DMR-1332208; DMR-1121262; 16.6554.2017/6.7
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 144; Journal ID: ISSN 1359-6454
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States); Colorado School of Mines, Golden, CO (United States); Cornell Univ., Ithaca, NY (United States); Siberian Physical Technical Inst., Tomsk (Russian Federation)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Ministry of Science and Education (Russian Federation)
Country of Publication:
United States
42 ENGINEERING; 36 MATERIALS SCIENCE; phase transformation; microstructures; finite elements; X-ray diffraction
OSTI Identifier: