Effect of terbium addition on the structure, phase constitution and hardness of the Ni49Mn29Ga22 alloy was studied. The Tb content varied in the range of 0-2 at.%. It was found that the Tb addition substantially refines the grain size, which dropped from 200-400 μm, for the Tb-free alloy, down to 30-50 μm for the 2 at.% Tb material. The terbium exhibited negligible solubility in the matrix phase and formed grain boundary layer. The mean composition of the boundary layer was: Tb - 16, Ni - 55, Mn - 7 and Ga - 22 at.%. The phase analysis revealed the presence of the following major phases in the alloys: Ni2MnGa, Ni3Ga. All the alloys studied exhibited martensitic structure at room temperature. The Tb addition did not affect the Curie temperature, which is consistent with the finding that Tb does not dissolve in the Ni2MnGa phase. However, it was found that Tb addition changed the phase transformations temperatures. The As temperature (martensite-to-austenite transformation starting temperature) and Ms temperature (martensite-to-austenite starting temperature) grow slightly for low Tb concentrations and subsequently decrease for higher the Tb contents. The Tb containing alloys exhibited increased hardness, by about 40%, which was apparently caused by the grain refinement. No significant effect of the Tb addition on the magnetic shape memory effect was observed.
The aim of the study was to develop an innovative processing method of magnetorheological elastomers (MRE). This method comprises optimization of the MRE structure in the context of their performance in the magnetic field. The influence of the amount of ferromagnetic particles and their arrangement in relation to the external magnetic field was investigated. As matrixes various elastomers, with different stiffness, were used. Their properties were compared with commercially available silicone rubbers. It was found that the structure of the MRE produced depends on the viscosity of the matrix before curing and the magnetic field strength applied. Two different magnetic field strengths were used: 100 and 300 mT. The amount of the carbonyl iron particles was equal to 1.5, 11.5 and 33.0 vol. %. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The influence of curing conditions on the thermal properties of the MRE was investigated. To evaluate the external magnetic field effect on the magnetorheological properties a deflection under magnetic field was measured. The experiment showed that application of the magnetic field increases stiffness of the material.