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

Journal Article · 22 June 2017 · Acta Materialia

DOI: https://doi.org/10.1016/j.actamat.2017.06.043 · OSTI ID:1394986

Ghassemi-Armaki, Hassan ^[1]; Leff, Asher C. ^[2]; Taheri, Mitra L. ^[2]; Dahal, J. ^[3]; Kamarajugadda, M. ^[3]; Kumar, K. Sharvan ^[1]

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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)

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 cyclic 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.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC52-06NA25396; SC0008274
• OSTI ID: 1394986
• Alternate ID(s): OSTI ID: 1550169
• Report Number(s): LA-UR-17-26380
• Journal Information: Acta Materialia, Vol. 136, Issue C; ISSN 1359-6454
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English