N. Mitrovic

Crystallization of the Fe-Cu-M-Si-B (M=Nb, V) amorphous alloys by direct-current Joule heating

The effects of dc Joule heating on structural, electrical and magnetic properties of Fe-Cu-M-Si-B (M=Nb, V) amorphous alloys have been investigated. Amorphous ribbons of these two systems were resistively heated by direct currents from 1.5 to 2.5 A. X-ray diffraction analysis has shown that changes in the relative electrical resistance correlate with the onset of the crystallization process. The F shape of hysteresis loops indicates the induction of transverse magnetic anisotropy as a result of applied treatments.

Applying quadraphonic transmission ultrasonic defectoscopy on standard aluminum materials

Abstract Quadraphonic transmission ultrasonic defectoscopy (QTUD) is a new method of ultrasound. This paper presents a detailed and systematic view of the measuring procedure that enables the discovery of a necessary optimal balance between, on the one side, efficiency and reliability of the QTUD measuring system, and on the other, minimizing the investment costs in the measuring components precision. This type of defectoscope applies relatively low frequencies of just a few tens of kilohertz that enable the necessary signal penetration during the measuring procedure. This paper shows a defectoscopic examination of the standard aluminum material AlMg3 with a defect that has been purposely created in need of developing the QTUD measuring procedure, whereby varied wave forms and the amplitude levels of signal have been used for the purpose of their optimization.

Low Frequencies for Cardboard Quality Assurance

Abstract During the ultrasound defectoscopy the ultrasound absorption factor inside the material is raised to the fourth power of frequency. In conjunction with the previously stated, the attenuation of the sound signal which is caused by the reflections of the sound inside the sample, the application of high frequency ultrasound in porous and hollow materials is very limited or even impossible. The frequencies are the reason for this, because they are in the range of just several megahertz, which are currently the main trend in the ultrasound examination. This paper presents a principle of this new method, including the experimental results from its application on the typical represent of product packaging material. Also, it is shown that the expressed absorption of ultrasound waves from porous and hollow structures can be avoided by applying the method with such low frequencies.

Magnetoimpedance Effect in Fe89.8Ni1.5Si5.2B3C0.5 Metallic Glass Ribbons

The magnetoimpedance (MI) effect in magnetically soft Fe89.8Ni1.5Si5.2B3C0.5 metallic glass ribbons is studied in this paper. As soft magnetic properties were determined by field induced anisotropy (and therefore by magnetic domain structure), ribbon samples were annealed under tensile stress in order to enhance induction of transverse anisotropy and to improve magnetoimpedance effect. Stress-annealing (SA) technique up to 420 0C/475 MPa/30 min. was used for tailoring electrical resistivity (ρ) and magnetic permeability (μ), i.e. two material properties that in classical skin effect determine the penetration depth δm and therefore have influence on MIeffect. The critical frequency of about 600 kHz was observed as the point with the initial increase of MI. Significant improvement of MI-response reaching the value Z/Z ≈ 25 %, after annealing at 420 0C, was recorded at driving frequency 4 MHz. The highest MI-element sensitivity was found for low magnetic field intensity where values of about 12 % / kA/m were attained.

Characterization of FeCoV alloy processed by PIM/MIM route

In this study the characterization of FeCo-2V alloys toroidal samples produced by PIM/MIM technology was presented. The feedstock for metal injection molding (MIM) was prepared by mixing starting FeCoV powder with a low viscosity binder. Green samples were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering was performed during 3.5 hours from 1370 oC to 1460 oC in hydrogen atmosphere in order to attain the appropriate mechanical and magnetic properties. Microstructure, hardness HV10 and magnetic hysteresis B(H) were investigated as a function of sintering temperature. Optimum combination of functional properties was observed after sintering at temperature of 1370 oC. In addition, magnetic properties were analyzed as frequency dependent and successfully simulated in operating frequency range from 5 Hz to 60 Hz.

Synthesis of magnesium titanates by mechanochemical method

The aim of this paper was mechanochemical preparation of magnesium titanates. Powder mixtures of starting oxides MgO and TiO2 were mechanically activated in a planetary ball mill for the time interval from 0 to 160 minutes. Structural, stereological, thermal characterizations were performed on produced powders. The effects of activation on morphology were investigated by scanning electron microscopy and particle size analyses, while the changes in the phase composition were determined by X-ray diffraction. It is determined that the first traces of MgTiO3 became detectable after 40 minutes of milling, while after 160 minutes the pure magnesium titanates were noticed. The differential thermal analyses and thermo gravimetric analysis, in temperatures range from 25 oC to 1100 oC, has been performed in order to investigate thermal behavior of the mixtures.

Improvement of the soft magnetic properties of Fe-based glassy alloys with a large supercooled-liquid region

Summary form only given. The ribbons of the Fe-(Al,Ga)-(P,C,B,Si,Ge) glassy alloys with a large supercooled-liquid region are characterized by some brittleness even in the as-cast state. On the other hand DC Joule heating is very effective in the simultaneous improvement of both magnetic and mechanical properties of the alloy in the annealed state. The authors present a study of optimization of the soft magnetic properties of melt spun Fe/sub 72-x/Nb/sub x/Al/sub 5/Ga/sub 2/P/sub 11/C/sub 6/B/sub 4/ (x=0,2) ribbons by furnace annealing (FA) and current annealing (CA).