Tunable Martensitic Transformation and Magnetic Properties of Sm-Doped NiMnSn Ferromagnetic Shape Memory Alloys

Abstract

NiMnSn ferromagnetic shape memory alloys exhibit martensitic transformation at low temperatures, restricting their applications. Therefore, this is a key factor in improving the martensitic transformation temperature, which is effectively carried out by proper element doping. In this research, we investigated the martensitic transformation and magnetic properties of Ni43Mn46-x SmxSn11 (x = 0, 1, 2, 3) alloys on the basis of structural and magnetic measurements. X-ray diffraction showed that the crystal structure transforms from the cubic L21 to the orthorhombic martensite and gamma (γ) phases. The reverse martensitic and martensitic transformations were indicated by exothermic and endothermic peaks in differential scanning calorimetry. The martensitic transformation temperature increased considerably with Sm doping and exceeded room temperature for Sm = 3 at. %. The Ni43Mn45SmSn11 alloy exhibited magnetostructural transformation, leading to a large magnetocaloric effect near room temperature. The existence of thermal hysteresis and the metamagnetic behavior of Ni43Mn45SmSn11 confirm the first-order magnetostructural transition. The magnetic entropy change reached 20 J·kg−1·K−1 at 266 K, and the refrigeration capacity reached ~162 J·Kg−1, for Ni43Mn45SmSn11 under a magnetic field variation of 0–5 T.

Effect of Different Mo Addition on Microstructure and Mechanical Properties of Cu-15Ni-8Sn Alloy

“…According to solution strengthening mechanism, III alloy with high concentration of solution atoms has higher hardness. At the early aging stage, the alloy hardness increases rapidly, which is attributed to the amplitude modulation decomposition transformation and the continuous precipitation of ordered phase [32][33][34]. It is well known that the hardness of Cu-15Ni-8Sn alloy will decrease significantly after a long time of aging, which is caused by DP [12].…”

Heat Treatment Effect on Thermal, Micro-Crystal Structure and Magnetic Behavior of Ni45Mn40Sn10Cu5 Heusler Shape Memory Alloy

“…Najan ul Hasan et al reported that an important factor affecting the transformation temperature is the change in matrix composition within the alloy. They considered that substitution of atoms with different sizes from the parent atoms causes expansion or contraction of the unit cell and hence lattice distortion [17]. It can be said that when the heat treatment temperature is at 900 C and 1100 C, the lattice structure of NiMnSnCu alloy is deformed due to shrinkage and expansion of atoms and therefore the martensite transformation temperature cannot be observed.…”

“…2. The obtained xray diffractograms were indexed according to the literature [17]. As seen in the diffractograms of the alloys heat treated at 700 o C and 900 o C, more cleavage occurred and the peaks became more pronounced compared to the diffractogram at 1100 o C. It was observed that most of the peaks disappeared at 1100 o C. When the peaks formed as a result of heat treatment were indexed, peaks belonging to two phases were found.…”