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Title: Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C is compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclicmore » mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less
Authors:
 [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [1]
  1. Brown Univ., Providence, RI (United States). School of Engineering
  2. Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Engineering
  3. Core Technologies, Minneapolis, MN (United States)
Publication Date:
Report Number(s):
LA-UR-17-26380
Journal ID: ISSN 1359-6454
Grant/Contract Number:
AC52-06NA25396; SC0008274
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 136; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Cyclic deformation; Shape memory alloys; Micropillars; Texture; Nanocrystalline
OSTI Identifier:
1394986