Studies on the structure of urethane magnetorheological elastomers (MREs),
with respect to their magnetic and mechanical properties, are reported. MREs
were obtained from a mixture of polyurethane gel and carbonyl-iron particles
cured in a magnetic field of 100 and 300 mT. Samples with different numbers of
particles (1.5, 11.5 and 33 vol%) were produced. The microstructure and magnetic
properties of the obtained MREs were studied. Also, the displacement of the
samples in an external magnetic field was examined using a specially designed
experimental set-up. The influences of the number of ferromagnetic particles and
their arrangement in relation to the external magnetic field were investigated.
It was found that the microstructure of the MREs depends on the number of ferrous
particles and the fabrication conditions. The orientation of the iron particles into aligned
chains is possible for a lower volume content of the ferromagnetic fillers. The high
carbonyl-iron volume content in the matrix leads to the formation of more complex
microstructures, similar to three-dimensional lattices. The magnetic measurements also
confirmed the existence of the microstructure anisotropy for the MREs with 1.5 and
11.5 vol% of iron particles. The structural and magnetic anisotropy has not been found in
the MREs with 33 vol% of Fe. To evaluate the effect of the external magnetic field on the
magnetorheological properties, the displacement under magnetic field, the compressive
strength, and the rheological properties were measured. The experiments showed that both
the particle content and the field strength used during curing have a significant effect
on the microstructure of the MREs and, in consequence, on their properties.
A new powder production method has been developed to speed up the search for novel alloys for additive manufacturing. The technique involves an ultrasonically agitated cold crucible installed at the top of a 20 kHz ultrasonic sonotrode. The material is melted with an electric arc and undergoes pulverization with standing wave vibrations. Several different alloys in various forms, including noble and metallic glass alloys, were chosen to test the process. The atomized particles showed exceptional sphericity, while powder output suitable for additive manufacturing reached up to 60%. The AMZ4 metallic glass powder remained amorphous below the 50 μm fraction, while tungsten addition led to crystallization in each fraction. Minor contamination and high Mn and Zn evaporation, especially in the finest particles, was observed in atomized powders. The innovative ultrasonic atomization method appears as a promising tool for material scientists to develop powders with tailored chemical composition, size and structure.
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