Abstract
The effects of cooling rate and annealed temperature on the state of atomic order and microstructure of L21 domains of Ni45Co5Mn36.6In13.4 ribbons are investigated comprehensively. The state of atomic order is quantitatively studied by in situ X-ray diffraction (XRD), and the microstructure of ordered domains is revealed by transmission electron microscopy (TEM). As-spun ribbons show B2 structure of low atomic order, exhibiting the dispersive L21 domains’ morphology. By applying heat treatment around the order–disorder transition temperature followed by furnace cooling or quenching into water, respectively, we found the strong dependence of ordered domains on cooling rates. Furnace cooling samples show L21 domains with small sized antiphase boundary, revealing a high degree of atomic order, while quenching hinders the formation of ordered domains. Annealing above the order–disorder transition temperature followed by quenching preserves the disordered atomic state with the mixture of L21 structure in B2 matrix.
Highlights
Academic Editor: Martin HeilmaierReceived: 27 July 2021Accepted: 9 September 2021Published: 16 September 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Ni-Mn-X (X = In, Sn, Sb) ferromagnetic shape memory alloys (FSMAs) are a kind of Heusler alloys [1], which have been extensively investigated for a few decades due to their excellent physical properties such as long-range magnetic ordering [2], giant magnetoresistance [3,4], magnetocaloric effects [5] and a perfect shape memory effect induced by the magnetic field in Co doped Ni-Mn-X Heusler alloys [6]
The atomic order and ordering domains morphology were analyzed as a function of The atomic order and and cooling orderingrates, domains morphology analyzed as a function of annealed temperature and the results arewere as follows: annealed temperature and cooling rates, and the results are as follows: 1. The evolution of atomic order is attributed to the atomic diffusion occurred in antiphase boundary (APB), 1
The evolution of atomic order is attributed to the atomic diffusion occurred in APB, revealed by L21 domains’ morphology
Summary
The addition of Co to Ni-Mn-In alloys has enhanced the magnetism of the austenite and results in an increase in magnetization change (∆M) at martensitic transformation [7] In these quaternary alloys, the entropy change (∆S) at the transformation and the physical properties strongly vary with atomic order [8,9]. The typical stoichiometric Heusler composition is X2 YZ, showing the L21 -ordered crystal structure (space group Fm3m) with next-nearest-neighbor atomic order indicted by (111), (311) and (331) superlattice reflections [10]. This face-centered (fcc) superlattice structure consists of eight body-centered cubic (bcc) sublattices.
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