Ferromagnetic shape memory alloys (FSMAs), which are potential candidates for future technologies (i.e., actuators in robots), have been paid much attention for their high work per volume and rapid response as external stimulation, such as a magnetic field, is imposed. Among all the FSMAs, the Ni–Mn–Ga-based alloys were considered promising materials due to their appropriate phase transformation temperatures and ferromagnetism. Nevertheless, their intrinsic embrittlement issue and sluggish twin motion due to the inhibition of grain boundaries restrict their practicability. This study took advantage of the single-crystal Ni–Mn–Ga cube/silicone rubber composite materials to solve the two aforementioned difficulties. The single-crystal Ni–Mn–Ga cube was prepared by using a high-temperature alloying procedure and a floating-zone (FZ) method, and the cubes were verified to be the near-{100}p Ni–Mn–Ga alloy. Various room temperature (RT) curing silicone rubbers were utilized as matrix materials. Furthermore, polystyrene foam particles (PFP) were used to provide pores, allowing a porous silicone rubber matrix. It was found that the elastic modulus of the silicone rubber was successfully reduced by introducing the PFP. Additionally, the magnetic field-induced martensite variant reorientation (MVR) was greatly enhanced by introducing a porous structure into the silicone rubber. The single-crystal Ni–Mn–Ga cube/porous silicone rubber composite materials are considered to be promising materials for applications in actuators.
Effect of elastic modulus of matrix on ferromagnetic motion of NiMnGa particles was investigated for NiMnGa particles embedded silicone matrix composites with or without containing polystyrene form particles (PFPs), which are regarded as pores. NiMnGa single crystal was fabricated by a floating zone method and a cube-shape particle was fabricated with the surface orientation parallel to [100], [010] and [001] directions at the parent phase state. The elastic modulus of matrix polymer was controlled by changing the number of PFPs. It was found that the elastic modulus of silicone was decreased with increasing the volume fraction of PFPs. The magnetic-field-induced martensite variant reorientation (MVR) was evaluated by the magnetization curves obtained using a vibration sample magnetometer, and the magnetic field required for the start of martensite variant reorientation was reduced by increasing the number of PFPs. The control of elastic modulus of matrix polymer is important and a dominant factor for the magnetic motion of NiMnGa/polymer composites.
Air-atomised pure aluminum powder together with photoluminescence powder LG was mechanically alloyed MAed using a vibrational ball mill, and the MAed composite powders were consolidated into bulk materials by spark plasma sintering SPS in order to fabricate the aluminum based composite materials exhibiting photoluminescence properties. Changes in hardness, particle sizes, constituent phases, luminance and microstructures of both the MAed powders and SPS materials were examined by microhardness measurements, scanning electron microscope, X-ray diffraction, luminance meter, and optical microscopy, respectively. The Vickers microhardness of the MAed powders increased by both an increase in MA time and the amount of LG powder addition. The mean particle size of the MAed powders for 60 min was smaller compared to that for 5 min. The Vickers hardness of the bulk SPS materials increased by both an increase in sintering temperatures and the amount of LG powder addition. No solid-state reactions could be detected in the bulk SPS materials during MA and SPS process. Bulk SPS materials showed luminance in a darkroom after they were irradiated by black light. Aluminum based composite materials exhibiting photoluminescence properties were successfully fabricated by a combination of MA and SPS process.
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