Abstract
We fabricated Ni37.5Co12.5Mn35Ti15 melt-spun ribbons at linear wheel speeds (WS) of 20 and 8 ms-1 (series A and B, respectively). The effect of a short time thermal annealing (30 min.) between 1023 K and 1173 K on the martensitic-like structural transition and the crystal structure, microstructure and magnetic entropy change ΔSM(T) curves and related parameters for as-solidified (AS) samples of series A were studied. Whereas the Curie temperature of austenite (AST) TCA keeps nearly constant, both the reduction of the solidification rate and the increase on the thermal annealing temperature increase the temperature of the structural transformation reducing the magnetization change across the AST to martensite (MST) transition. The martensitic transformation (MT) in AS samples undergoes from a B2-type ferromagnetic (FM) AST with TCA = 328 K to a monoclinic martensite (MST); SEM images evidenced a partially grain-oriented microstructure formed by columnar in shape-elongated grains with their major axis oriented along the thermal gradient during solidification. Magneto-structural transition for AS ribbons of series A occurs in the vicinity of room temperature and is accompanied by a magnetization change of around 63 Am2kg-1. For a magnetic field change of 2 T these samples showed a maximum magnetic entropy change |ΔSM|max of 13.8 (9.5) J kg-1 K-1 for the MST→AST (AST→MST) transformation. This is below the previously reported for this alloy composition (27.2 J kg-1 K-1), and is related to the broader magneto-structural transition.
Highlights
The sizeable magnetocaloric,1–4 elastocaloric,5 barocaloric6 and magneto-strain7 effects around temperature (RT) associated to the martensitic transformation (MT) found in the newly reported all3d-metal quaternary Ni-Mn-Co-Ti alloys are a strong motivation for their further investigation
The main difference between them lies in the average ribbon thickness ⟨d⟩ that, as expected,8 is higher in samples produced at a higher solidification rate
In which melt-spun ribbons of the all-3-d-metal Heusler alloy Ni37.5Co12.5Mn35Ti15 were produced at two different wheel speeds (20 ms-1 and 8 ms-1), it was concluded that: (a) the structural transition temperature strongly depends on the solidification rate
Summary
The sizeable magnetocaloric, elastocaloric, barocaloric and magneto-strain effects around temperature (RT) associated to the martensitic transformation (MT) found in the newly reported all3d-metal quaternary Ni-Mn-Co-Ti alloys are a strong motivation for their further investigation. These alloys show excellent mechanical properties, which contrast with the widely studied (Ni-MnX)-based Heusler alloys (X = Ga, In, Sn and Sb) that are quite brittle. In most of the early experimental reports, these alloys, both in bulk or as melt-spun ribbons, showed a broad magnetostructural transition. B2-type crystal structure to a weak magnetic martensite with a monoclinic crystal structure (P2/m). With the increase in the Co content, the Curie temperature of AST TCA increases, whereas the temperature of the structural transition can be tuned in a wide temperature interval from above to well below room temperature (RT). From the available literature it seems that the temperature of the MT is strongly influenced by microstructural features. In most of the early experimental reports, these alloys, both in bulk or as melt-spun ribbons, showed a broad magnetostructural transition.
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