A eutectic dual-phase design towards superior mechanical properties of heusler-type ferromagnetic shape memory alloys

Abstract

Heusler-type ferromagnetic shape memory alloys possess attractive multifunctional properties, including magnetic field induced shape memory effect, magnetoresistance and magnetocaloric effect, owing to the unique concurrent magnetic and martensitic transformations. However, these intermetallics generally exhibit intrinsic high brittleness and low strength, which severely impede their workability for processing and applicability in real use. In this study, we demonstrate a new grain refining strategy by means of eutectic solidification to improve the mechanical properties in Ni-Mn-Sn-Fe alloys. In a fully eutectic microstructure, the average γ lamellae thickness was refined to ~170 nm and the composite showed a compressive strength of 1950 MPa, ductility of 19.5%, Young's Modulus of 38 GPa, pseudoelasticity of 3.2% and high mechanical cyclic stability. The high mechanical performance is attributed to the effect of departmentalisation of the brittle Heusler alloy by the densely distributed γ phase fine lamellae in resisting crack propagation. The eutectic Heusler composite exhibited a metamagnetic phase transformation, with a magnetic entropy change of 10.2 J/kg•K and a refrigeration capacity of 181 J/kg in a field change of 5 T.

Grain Size Effect of the γ Phase Precipitation on Martensitic Transformation and Mechanical Properties of Ni–Mn–Sn–Fe Heusler Alloys

“…Figure 3 shows the XRD spectra of As-cast, A4 and A32 samples measured at room temperature. The diffraction peaks of each phase of the samples are indexed according to the literature [ 27 , 28 , 36 , 37 , 38 ]. It is seen that the As-cast sample contains mixed phases of L2 1 austenite, 4O martensite and fcc γ phase at room temperature.…”

“…Figure 4 shows the evolution of martensitic transformation with annealing time. Figure 4 a presents the DSC curves of the As-cast and A1–A32 samples, which exhibited the L2 1 ↔4O transformation peaks [ 28 ]. The A120 sample did not show any transformation peaks on the DSC curve within the temperature range tested.…”

“…Due to its brittleness, grain refinement of the γ phase by deformation and recrystallization is practically impossible in these alloys. In our previous reports, a new grain refining strategy of the γ phase was introduced using the eutectic solidification method with a proper selection of alloy compositions, as demonstrated in Ni–Mn–Sn–Fe alloys [ 27 , 28 ]. The ultrafine eutectic lamellae represents a typical isotropic fine grained microstructure that exhibited high strength and ductility.…”

All-d-Metal Full Heusler Alloys: A Novel Class of Functional Materials

“…Unfortunately, as mentioned before, the strong covalent character of the p−d mechanism originates a brittle behavior for X 2 YZ Heusler systems, 36 a rather problematic feature concerning the technological exploration of its shape memory behavior and caloric effects.…”

Simultaneous improvement of martensitic phase transition and ductility in Cu-doped and/or alloyed all-d-metal Ni2MnTa Heusler compounds

“…[6][7][8][9][10] Practically, the p-d covalent hybridization could result in brittleness in Heusler compounds and consequently do harm to the further application. [11][12][13] It is urgent to explore the Heusler compounds with improved ductility and tunable functional properties. To improve the ductility of Heusler compounds, Wei and collaborators developed all-d-metal Heusler compounds.…”