Abstract
Severe plastic deformation (SPD) is widely considered to be the most efficient process in obtaining ultrafine-grained bulk materials. The aim of this study is to examine the effects of the SPD process on Ni-Fe-Ga ferromagnetic shape memory alloys (FSMA). High-speed high-pressure torsion (HSHPT) was applied in the as-cast state. The exerted key parameters of deformation are described. Microstructural changes, including morphology that were the result of processing, were investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to study the two-phase microstructure of the alloys. The influence of deformation on microstructural features, such as martensitic plates, intragranular γ phase precipitates, and grain boundaries’ dependence of the extent of deformation is disclosed by transmission electron microscopy. Moreover, the work brings to light the influence of deformation on the characteristics of martensitic transformation (MT). Vickers hardness measurements were carried out on disks obtained by SPD so as to correlate the hardness with the microstructure. The method represents a feasible alternative to obtain ultrafine-grained bulk Ni-Fe-Ga alloys.
Highlights
Shape memory alloys (SMA) are functional materials which are predominantly used as actuators [1].On the other hand, magnetic shape memory alloys (MSMA) may be used both as microactuators and displacement/force sensors or dampers [2,3]
Our aim is to achieve severe plastic deformation in Ni-Fe-Ga MSMA applying a novel technique named high-speed, high-pressure torsion (HSHPT) that brings about grain refinement
The High-speed high-pressure torsion (HSHPT) processing technique combines a very efficient grain refining with the capability of keeping shape memory properties due to dynamic recrystallization as our research shows on other metallic alloys [12,13,14]
Summary
Shape memory alloys (SMA) are functional materials which are predominantly used as actuators [1]. Magnetic shape memory alloys (MSMA) may be used both as microactuators and displacement/force sensors or dampers [2,3]. In these alloys responsible for the shape memory effect is martensitic transformation (MT) in addition to the transition of magnetic order-disorder [4,5]. Some of the most promising MSMA are Heusler-type ferromagnetic SMAs [6,7]. Heusler alloys are intermetallic compounds with the stoichiometry X2 YZ, where X and Y represent transition metals and
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