M. Kubisztal

Magnetic Shielding Effectiveness of Iron-Based Amorphous Alloys and Nanocrystalline Composites

This paper refers to magnetic field shielding effectiveness Sh of the selected iron-based amorphous alloys and some magnetic composites. The measurement conditions were chosen regarding the potential sources such as energetic lines or electric devices. As it was shown, the shields made of amorphous and optimized (in amorphous phase) melt spun ribbons can be applied as highly efficient and flexible shields. In the group of the tested alloys, the highest S_H reveal (at H = 110 A/m and f = 55 Hz): Fe₈₄ Cr₂ B₁₄ (95%) and optimized Fe₇₂ Co₁₀ Nb₆ B₁₄ (97%) and Fe₈₀ Nb₆ B₁₄ (92%). In the case of the tested composites, a significant decrease of S_H was observed. The shielding effectiveness decreases with decreasing size of magnetic addition due to breaking magnetic flux circuit and dipolar interactions between particles. For the composite with magnetic flakes of 4 mm in diameter S_H is about 60%; therefore, it can be applied as coatings in order to fulfill human protective standards. For the composites with micro and nano-sized magnetic powder S_H does not depend of the composition which suggests that a response to a magnetic field is fully influenced by the demagnetization effect.

Young's modulus and adhesion coefficient of amorphous Ni-P coatings on a metal substrate

In the present paper the Youngs modulus and adhesion coefficient of amorphous Ni–P coatings obtained from aqueous solutions were determined. The measurements were carried out using a vibrating reed apparatus. In the temperature range 550–590 K, crystallization of Ni and formation of nickel phosphide Ni3P were observed. The Youngs modulus of Ni–P amorphous layers on stainless steel at room temperature was found to be about 112 GPa. The adhesion coefficient γ of the examined layers depends on the layer thickness a f and strongly decreases for a f > 8 μm. This dependence corresponds to the change of the relative adhesion coefficient of about 40% for 8 μm < a f < 15 μm. It was also shown that the adhesion coefficient does not depend on the temperature, at least in the range 300–550 K.

Magnetic and Elastic Properties of Nanocomposites Containing Soft (Ni) and Hard (SrFe12O19) Magnetic Particles

In the present paper magnetic and elastic properties of the Ni+SrFe12O19 nanocomposites were examined in detail. Samples were in two forms: i) mechanically pressed cylindrical pellets and ii) filled polymer (amine-epoxy resin) coating on aluminum substrate. The so called apparent Young’s modulus was determined by measurements of the free flexural vibrations frequency by means of vibrating reed technique. Magnetic research was carried out using VSM magnetometer. It was shown that replacement of SrFe12O19 with nano Ni powder results in an increase in material resistivity to elastic deformation. The influence of size reduction of SrFe12O19 powder particles on magnetic parameters of the studied nanocomposites were discussed in detail.

Effect of Ball Milling on Structure and Magnetic Properties of Fe-Nb-B-Tb Bulk Nanocrystalline Alloys

It was shown that pulverization of the examined alloys cause a decrease of mean diameters of nanocrystallites, a change of the phase composition and affects magnetic properties. For the alloy with x=0.08 magnetization remanence at T=300 K increases about two times with remaining constant Hc while for x=0.12 Hc decreases from 1.16 t to 0.36 T. The observed effects were attributed to the phase structure changes and breaking of direct magnetic intergrain coupling

Structure and Phase Transformation in Ni-Co-Mn-In Ferromagnetic Shape Memory Alloys

In the present study the series of the Ni46.2Co5.0Mn36.1In12.6, Ni48.7Co5.2Mn34.4In11.6 and Ni45.6Co4.8Mn36.4In13.2 alloys (at. %) were studied. The influence of the indium addition on structure and phase transitions was studied. All alloys were annealed at 900°C for 24 hours and then slowly cooled in the furnace. After annealing all of the studied alloys showed the macrostructure of radially oriented columnar grains, which lied in the direction perpendicular to the casting axis. For the alloy containing about 13 at. % of indium the monoclinic 14M modulated martensite was stated at room temperature. Apart from the modulated martensite in a1_133 alloy the gamma phase was also observed. For alloy with higher indium content the mixture of cubic L21 parent phase and cubic gamma phase was identified. All studied alloys showed one-step martensitic transformation.

Preparation and Structural Examinations of Gd+Ni Nanocomposites

In the paper Gd+Ni nanoparticles were obtained using chemical reaction of Gd nanopowder in the bath based on C4H6O4Ni (pH=7) at temperature 323 K. TEM examinations show Gd+Ni nanoparticles (about 200 nm) covered by GdF3 intermediate layer and Ni-P final layer Magnetization vs. temperature (5-320 K) show the Curie point of Gd at 290 K and at low temperature a paramagnetic component related to GdF3. The obtained Gd+Ni nanopowder of 200 nm in diameter can be used in future application without fear of oxidation.