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Materials 2016, 9(5), 382; doi:10.3390/ma9050382

Microstructural Anisotropy of Magnetocaloric Gadolinium Cylinders: Effect on the Mechanical Properties of the Material

1
Institute of Metals and Technology, Ljubljana 1000, Slovenia
2
Faculty of Mechanical Engineering, University of Ljubljana, Ljubljana 1000, Slovenia
3
Faculty of Natural Sciences and Engineering, University of Ljubljana, Ljubljana 1000, Slovenia
*
Author to whom correspondence should be addressed.
Academic Editor: Beatriz Noheda
Received: 24 March 2016 / Revised: 26 April 2016 / Accepted: 12 May 2016 / Published: 17 May 2016
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Abstract

The development of advanced materials and technologies based on magnetocaloric Gd and its compounds requires an understanding of the dependency of mechanical properties on their underlying microstructure. Therefore, the aim of the study was to characterize microstructural inhomogeneities in the gadolinium that can be used in magnetocaloric refrigeration systems. Microstructures of magnetocaloric gadolinium cylinders were investigated by light microscopy and FE-SEM (Field Emission Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy), and BSE (Back-scattered Electrons) in both the extrusion and the extrusion-transversal directions. XRD (X-ray Diffraction) analyses were performed to reveal the presence of calcium- and fluorine-based compounds. Metallographic characterization showed an oxidized and inhomogeneous microstructure of the cross-sections. The edges and the outer parts of the cylinders were oxidized more intensively on the surfaces directly exposed to the processing tools. Moreover, a significant morphological anisotropy of the non-metallic inclusions was observed. CaF inclusions act as active nucleation sites for internal oxidation. The non-metallic, Ca- and F-containing inclusions can be classified as complex calciumoxyfluorides. The solubility of Er and Yb in the CaF was negligible compared to the Gd matrix and/or the oxide phase. Lower mechanical properties of the material are a consequence of the lower structural integrity due to selective oxidation of surfaces and interfaces. View Full-Text
Keywords: magnetocaloric; Gadolinium; inclusions; selective oxidation; mechanical properties magnetocaloric; Gadolinium; inclusions; selective oxidation; mechanical properties
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Petrovič, D.S.; Šturm, R.; Naglič, I.; Markoli, B.; Pepelnjak, T. Microstructural Anisotropy of Magnetocaloric Gadolinium Cylinders: Effect on the Mechanical Properties of the Material. Materials 2016, 9, 382.

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