Marcin Leonowicz

Compressive strength of aluminium foams

Compressive strength was measured for aluminium foam specimens having different density and size. Larger specimens exhibited lower mean strength and narrower scattering of the strength values versus material density than the smaller ones. This behaviour is explained in terms of a greater probability of the existence of lower density regions in the former specimens. Both small and large low-density samples show more reproducible properties than the higher density ones.

Application of the shock compaction technique for consolidation of hard magnetic powders

A shock compaction technique has been successfully applied for the consolidation of hard magnetic powders without appreciable changes in the phase structure and grain size. Pr–Fe–B and Sm–Fe–N materials, prepared with the application of melt spinning and mechanical alloying, respectively, were shock compacted with a shock wave speed of 1200 m/s and a pressure of 4.4 GPa. We found that the coercivity of high RE containing material, for which the magnetic hardness is controlled by good magnetic separation of magnetic grains by a RE-rich paramagnetic phase, decreases slightly, by ∼5 %, due to the closer proximity of the crystallites in a dense material. For low RE, exchange coupled materials, the densification does not change the coercivity.

Magnetic properties and microstructure of Nd16Fe76−xMxB8 magnets (M = Ga, Cr, Nb, Bi, Sn, Zr, W, V, Mo, Mn)

Abstract The effect of a partial substitution of Fe by Ga, Cr, Nb, Bi, Sn, Zr, W, V, Mo on the magnetic properties of Nd-Fe-B alloys is presented. The additive elements, which are dissolved in the hard magnetic phase and create inclusions in the matrix, may effect the increase of the coercivity and improve its temperature coefficient. Coercivity mechanisms are determined by the dimensions of the precipitates.

Investigation of the effect of para-aramid fabric impregnation with shear thickening fluid on quasi-static stab resistance

The main research objective of this study was to investigate the effect of the impregnation of Twaron® fabric with various shear thickening fluids (STFs) on the stab resistance at quasi-static conditions—being the main parameter characterizing the future application of the impregnated textiles in the scope of the new functionality of the elaborated protection of the multi-layer system. It was found that the STF/Twaron® fabric composites required significantly higher loading than the untreated fabric to achieve spike penetration. In the composite fabric tests, the spike did not fully puncture the material.

Arc Plasma Synthesis of (Fe-Nd-B) - Containing Carbon Encapsulates

The formation of novel carbon nanostructures containing Fe-Nd-B nanocrystallites is reported. Tests were performed in a DC arc plasma reactor under He atmosphere using (Fe-Nd-B)- filled anodes. The influence of the operational parameters pressure and anode composition on the product morphology was studied. The products were analyzed by HR TEM, MFM and magnetic measurements. Emission spectroscopy was performed to determine the temperature and C2 radical distribution in the arc.

Effect of the processing conditions on the microstructure of urethane magnetorheological elastomers

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.

Effect of gallium additions on the magnetic properties of die-upset forged Fe-Nd-B type melt spun alloys

Abstract The magnetic properties of melt spun ribbon, hot pressed and die-upset forged Fe 79 − x Nd 15 B 6 Ga x ( x = 0–1.5 at%) magnets have been investigated. It has been found that Ga additions up to 1 at% significantly increase the coercivity of the Fe-Nd-B alloys but further additions cause a dramatic decrease in coercivity. Gallium contents to 1 at% do not influence the Curie temperature of the magnets although the melting point of the grain boundary Nd-rich phase is significantly reduced. The optimum properties for the die-upset magnet have been established at 0.25 at% Ga whereby a 25% increase in coercivity has been observed with little loss in remanence and energy product. We attributed the initial changes in the magnetic properties of Fe-Nd-B dieupset forged magnets containing Ga to the reduction of the melting temperature of the boundary phase resulting in better magnetic isolation of the hard magnetic grains and the pinning effect of the precipitates of Ga-rich phases.

Formation, Structure and Magnetic Properties of Polymer Matrix Nanocomposites Processed by Thermal Decomposition of the Fe(III)Co(II) Acrylate Complex

Structure and magnetic properties of polymer matrix nanocomposites, processed by pyrolysis of the Fe(III)Co(II) acrylate complex, were investigated. It was shown that thermal transformation of the complex studied consisted of three macrostages: dehydration, solid state polymerisation and decarboxylation of a metallopolymer form. The main products of the decomposition were nanoparticles stabilised by polymeric matrix. The crystalline phases, which were found in the fully processed material, were Fe3O4, CoFe2O4 and CoO. The mean crystallite size was 10nm. In the intermediate stages of the thermolysis iron was present in the forms of FeIII (trivalent low – spin iron), Fe2+(divalent high – spin iron) and Fe3O4. The hysteresis loops measured at temperatures below 200K were opened and shifted towards negative field. The coercivity and remanence showed room temperature values of 0.18T and 15.5mT, respectively.

New ferromagnetic material by exothermic reaction of a polymetallic complex compound MAX (M = Fe3++Co2+, A = SO32−, X = 3-amino-1,2,4-triazol)

Abstract A new ferromagnetic material FP prepared by thermal reaction in a polymetallic complex compound MAX ( M = Fe 3+ + CO 2+ , A = SO 3 2− , X = 3-amino-1,2,4-triazol) has been developed. The constituents are cheap, commercially available and the fabrication of the material is easy. The green compacts, prepared by a powder metallurgy route, exhibit isotropic magnetic properties with B r = 0,13 T and J H c = 60 kA m −1 . The properties can be affected by annealing and modification of the composition.

The effect of tungsten addition on the magnetic properties and microstructure of SmFeN–α-Fe nanocomposites

Abstract The effect of tungsten addition, in the range of 0–17 at.%, on the magnetic properties and microstructure of SmFeN–α-Fe permanent magnet nanocomposites is presented. The magnets were prepared by mechanical alloying of elementary powders of Sm, Fe and W, followed by annealing and nitriding. The addition of tungsten leads to initial increase and further decrease of the coercivity with a maximum value of 250 kA/m for 7 at.% W. The remanence, however, continuously decreases from 1.2 T for 0% W down to 0.7 T for 17 at.% W. The maximum value of (BH)max, (120 J/m3), was obtained for 2 at.% W. The measurements of Curie temperature vs. W content showed a constant and decreasing values for α-Fe and the Sm2Fe17 phase, respectively. This behaviour can be explained by the dissolution of some W atoms in the Sm2Fe17 phase. X-ray diffraction analysis indicated, beside the α-Fe and Sm2Fe17 phases, the existence of pure W in the microstructure. Addition of W leads to reduction of the α-Fe crystallite size (20 nm for 0% W, 18 nm for 7% W and 8 nm for 17% W). The high resolution electron microscopy investigations show randomly distributed small (below 20 nm) crystallites of tungsten. Thus for a small amount of W the remanence is still substantially enhanced. The increase of the coercivity, for W contents up to about 7 at.%, can possibly be attributed to increased magnetic anisotropy of the Sm2(Fe,W)17N3 phase.