Effect of porosity on the magneto-mechanical behavior of polycrystalline magnetic shape-memory Ni–Mn–Ga foams. (15th June 2015)

• Record Type: Journal Article
• Authors: Witherspoon, C.; Zheng, P.; Chmielus, M.; Dunand, D.C.; Müllner, P.
• Is Part Of: Acta materialia. Volume 92(2015)
• Page Start: 64
• Page End: 71
• Publication Date: 2015-06-15
• Subjects: Martensitic phase transformation -- Foam architecture -- Thermal cycling -- Ni2MnGa -- Heusler alloys; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2015.03.038
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Porosity in polycrystalline Ni–Mn–Ga alloys reduces internal constraints imposed by grain boundaries which suppress magnetic-field-induced strain in non-porous, polycrystalline magnetic shape-memory alloys. We present here a systematic study of the porosity effect on the magneto-mechanical properties of polycrystalline Ni–Mn–Ga foams. Starting from replicated foams created by casting with ceramic space holders, their porosities were increased by successive acid dissolution steps after which the magnetic-field-induced strain was measured, for each porosity level, after thermo-magneto-mechanical training. Consistently, the magnetic-field-induced strain increased with increasing porosity, in the extreme case by one order of magnitude for a small porosity increase of 1.3%, demonstrating that removal of constraints by porosity is responsible for the high magnetic-field-induced strain in polycrystalline Ni–Mn–Ga foams.