A Combinatorial Study For Interdiffusion, Crystallography And Mechanical Behavior Of Ni-Mn-Ga Alloys

Keywords

Martensite; Nanoindentation; NiMnGa; TEM

Abstract

The ferromagnetic shape memory and magnetocaloric properties of NiMnGa alloys are closely related to the martensitic transformation from high temperature austenitic phase to low temperature martensitic phase. The transformation temperature and the resulting microstructure and crystallography of the martensites can be very complex, but are crucial to the optimization of the material performance. A combinatorial study with a series of solid-to-solid diffusion couples and various characterization techniques, including scanning electron microscopy, focused ion beam, transmission electron microscopy, electron probe microanalysis, and nano-indentation, was carried out to investigate the microstructural and crystallographic development, and mechanical properties in NiMnGa alloys. Both austenitic and martensitic phases were found at room temperature in each diffusion couple with a clear interphase boundary. Crystallographic variations in martensitic phase, including non-modulated (NM) martensite and modulated (5M or 7M) martensite, were found in the diffusion couples. All martensitic microstructure consists of variants with different orientations and the twinning relationship. A decrease of reduced elastic modulus (Er) was obsErved with Ni substituting for Ga in the austenitic phase. HowevEr, an opposite trend of an increase in Er was found in the martensitic phase. The softening of the elastic constants near the vicinity of martensitic transformation contributed to a sharp decrease in Er near the intErphase boundary. The measured Er had a largEr scattEr for the martensitic phase than that for the austenitic phase.

Publication Date

1-1-2016

Publication Title

Defect and Diffusion Forum

Volume

371

Number of Pages

153-159

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.4028/www.scientific.net/DDF.371.153

Socpus ID

85014049825 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85014049825

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