Title

An In Situ Neutron Diffraction Study Of Shape Setting Shape Memory Niti

Keywords

Blocking stress; Neutron diffraction; NiTi; Shape setting; Stress relaxation

Abstract

A bulk polycrystalline Ni49.9Ti50.1 (at.%) shape memory alloy specimen was shape set while neutron diffraction spectra were simultaneously acquired. The objective was to correlate internal stress, phase volume fraction, and texture measurements (from neutron diffraction spectra) with the macroscopic stress and shape changes (from load cell and extensometry measurements) during the shape setting procedure and subsequent shape recovery. Experimental results showed the evolution of the martensitic transformation (lattice strains, phase fractions and texture) against external constraints during both heating and cooling. Constrained heating resulted in a build-up of stresses during the martensite to austenite transformation, followed by stress relaxation due to thermal expansion, final conversion of retained martensite, and recovery processes. Constrained cooling also resulted in stress build-up arising from thermal contraction and early formation of martensite, followed by relaxation as the austenite fully transformed to martensite. Comparisons were also made between specimens pre-shape set and post-shape set with and without external constraints. The specimens displayed similar shape memory behavior consistent with the microstructure of the shape set sample, which was mostly unchanged by the shape setting process and similar to that of the as-received material. © 2013 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Publication Date

6-1-2013

Publication Title

Acta Materialia

Volume

61

Issue

10

Number of Pages

3585-3599

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1016/j.actamat.2013.02.040

Socpus ID

84876889858 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/84876889858

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