In situ transmission electron microscopy studies of directionally solidified Ni-Mn-Ga ferromagnetic shape memory alloys

From National Research Council Canada

DOI	Resolve DOI: https://doi.org/10.1016/j.msea.2003.11.078
Author	Search for: Bennett, J. C.; Search for: Hyatt, C. V.; Search for: Gharghouri, M. A.; Search for: Farrell, S.; Search for: Robertson, M.; Search for: Chen, J.; Search for: Pirge, G.
Format	Text, Article
Subject	Bridgman growth; Microstructure; NiMnGa alloys; TEM
Abstract	Transmission electron microscopy has been used to examine the microstructure and transformation behaviour of four non-stoichiometric Ni-Mn-Ga oriented polycrystalline alloys grown by seedless Bridgman solidification. Despite similar average compositions, the observed microstructures and transformation temperatures of these alloys varied significantly. For alloy A with nominal composition Ni50.1Mn28.2Ga21.7 (at.%), the Heusler ordered (L21) austenite phase was observed to exhibit characteristic "tweed" strain contrast at room temperature. On cooling, sharp satellite reflections associated with the formation of an intermediate phase appeared at ~200°K, prior to a martensitic transformation at ~190°K which generated a microstructure consisting predominately of seven-layer martensite with regions of five-layer martensite. For alloys B (nominal Ni49.3Mn28.6Ga22.1) and C (nominal Ni49.3Mn28.8Ga21.9), the martensitic transformation occurred slightly below room temperature and the TEM images revealed a fine-scale intermixture of austenite with five-layer, seven-layer and non-modulated martensite. The microstructure of alloy D (nominal Ni49.3Mn28.8Ga21.9), with a transformation temperature somewhat above room temperature was composed predominately of seven-layer martensite. The results indicate that small microscale variations in composition and/or parent phase grain size have a significant effect on the transformation behaviour of directionally solidified Ni-Mn-Ga alloys.
Publication date	2004-07-25
In	Materials Science and Engineering A 378, no. 1-2 (25 July 2004): 409–414.
Language	English
NRC publication	This is a non-NRC publication "Non-NRC publications" are publications authored by NRC employees prior to their employment by NRC.
NPARC number	12330201
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Record identifier	35de4c32-ca5c-4cb4-b257-da75cd791b19
Record created	2009-09-10
Record modified	2020-04-17

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