Magnetocaloric Effect, Structure, Spinodal Decomposition and Phase Transformations Heusler Alloy Ni-Mn-In

Abstract

Ni46Mn41In13 (close to 2-1-1 system) Heusler alloy was studied by magnetization measurement dependence on the temperature in magnetic fields of up to 13.5 T. The magnetocaloric effect measured by the direct method in quasi-adiabatic conditions showed a maximum value of ∆Tad = −4.2 K at a temperature T = 212 K in a magnetic field of 10 T in the region of martensitic transformation. The structure of the alloy was studied by transmission electron microscopy (TEM) as a function of the temperature and the thickness of the sample foil. In the temperature range from 353 to 215 K, at least two processes were established. The results of the study indicate that the concentration stratification occurs according to the mechanism of spinodal decomposition (conditionally spinodal decomposition) into nanoscale regions. At a temperature of 215 K and lower, martensitic phase with 14 M modulation is observed in the alloy at thicknesses greater than 50 nm. Some austenite is also observed. In foils with thickness of less than 50 nm in a temperature range from 353 to 100 Km only the initial austenite, which has not transformed, was found.

Influence of the Cooling Rate on Austenite Ordering and Martensite Transformation in a Non-Stoichiometric Alloy Based on Ni-Mn-In

“…Similar behavior is observed in thin films with a thickness of 50-150 nm. An increase in the proportion of surface energy relative to volumetric energy is qualitatively similar to stress fields that expand the region of existence of ferromagnetic austenite and thereby lower the temperature Mf to 160 K. For the slowly cooled alloy see [5]. Thermogravimetric analysis specified the Curie temperature, and it was 321 K for the slowly cooled sample and 305 K for the quenched sample, see Figure 2.…”

“…A tweed contrast is observed on the bright and dark field TEM images of the austenite structure of the alloy under study (Figure 9a). At slow cooling rates from the melt, the nonstoichiometric Ni-Mn-In alloy can decompose into regions that differ both in chemical composition and in different levels of ordering, which leads to the formation of a modulated periodic austenite structure [5]. The dark-field image (Figure 9b) obtained in the 02-2 reflection (all diffraction patterns are also indexed according to the L2 1 ordering) shows a contrast from APBs in which the L2 1 superstructure is broken and the order of atoms is close to the B2 structure.…”

“…When cooled from the melt, alloys with the Heusler (for example X 2 YZ, XY 2 Z, and other) structure can undergo a series of disorder-order transitions, A2 → B2 → L2 1 (D0 3 , C1 b , and some others), depending on the occupancy of positions between the X, Y, and Z sublattices [4]. Alloys based on the Ni-Mn-In system of a non-stoichiometric composition are prone to decay into an energetically favorable structure with a 2-1-1 stoichiometry and the rest of the alloy, which forms various structures with different compositions [5]. Depending on the degree of atomic ordering, it is assumed that the Ni-Mn-In compound will contain structural domains and APB formed during the transition from the partially ordered B2 phase to the ordered L2 1 .…”

Recent Advances in Additive Manufacturing of Soft Magnetic Materials: A Review

“…Such multi-step processing techniques, involved in ingot metallurgy practices, play a significant role in the magnetic behavior of these alloys. However, during conventional manufacturing processes, some solid-state disorder–order phases tend to form, reducing the workability of soft magnetic alloys and limiting the optimization of the chemical composition of the alloy [ 39 , 40 , 41 ]. For example, in high-silicon Fe–Si alloys, there is a tendency during cooling to form phases with oriented structures through lattice rearrangement into B2 and D03 phases [ 42 , 43 ].…”