Relaksacje migracyjne w ciałach stałych

W pracy szczegółowo przedstawiono ogólne podejście do procesów relaksacyjnych, jako metody badawczej stosowanej zarówno w fizyce ciała stałego jak i inżynierii materiałowej. Szczególną uwagę poświęcono relaksacjom migracyjnym, dla których mechanizm zjawiska kontrolowany jest przez dyfuzję. W kolejnych rozdziałach omówiono ideę równań materiałowych, procesy dyfuzyjne, formalny opis stanów nierównowagowych w podejściu równań kinetycznych, tzw. uniwersalną funkcję odpowiedzi (model Coupling), oraz techniki eksperymentalne stosowane w praktyce badawczej uzupełnione o stosowne przykłady. W obszernym rozdziale 7-mym (ponad połowa całego opracowania) przedstawiono szczegółowe problemy badawcze: dyfuzja atomów roztworu międzywęzłowego w metalach bcc (relaksacja Snoeka), dyfuzja atomów roztworu substytucyjnego (relaksacja Zenera), relaksacje w układzie silnie oddziałujących dipoli (tlenki o strukturze fluorytu), relaksację wiskosprężystą (model fraktalny) oraz relaksację strukturalną w stopach amorficznych na bazie żelaza

Influence of cooling rate on magnetic properties of (Fe80Nb6B14)(1-x)Tb-x type of bulk nanocrystalline alloys

The paper refers to magnetic properties of the (Fe80Nb6B14)1xTbx (x = 0:06 and x = 0:08) bulk nanocrystalline alloys prepared using the vacuum suction casting technique. The samples were in the form of rods with diameters of d = 1:5 mm, 1 mm and 0.5 mm. It was shown that for the alloys with x = 0:08 the signi cant magnetic hardening with the decrease of sample diameter was observed. For d = 0:5 mm the coercive eld equals 2.46 T and the maximum energy product jJHjmax = 77:2 kJ/m3

Non-destructive method of determination of elastic properties and adhesion coefficient of different coating materials

Purpose: The paper presents a non-destructive method of determination of Young’s modulus and adhesion coefficient of different coating materials (metallic coatings, polymer, composite etc.). Some of the results obtained by applying this method are discussed in detail. Design/methodology/approach: The presented method consists in measuring the dynamic response of the examined material in the form of a flat rectangular bar subjected to external periodic mechanical stress i.e. the so called vibrating reed technique. General equations describing elastic properties of the sample consisting of a substrate and a deposited coating are derived and discussed in detail. Findings: It was shown that the application of the proposed approach to the metallic, polymeric and composite coatings allowed to obtain a quantitative data concerning the change of both the elastic properties and the adhesion coefficient with a change of: coating thickness, measurement temperature, chemical composition of coating, surface preparation or in the case of epoxy resin coatings with a change of curing time or curing temperature. Research limitations/implications: The proposed method can be applied in many scientific problems in the field of coating materials (e.g. elastic properties of porous coating, crystallization of amorphous coating, adhesion of different polymeric coatings). Practical implications: It was shown that the described method can be successfully used in optimisation of some technological processes of deposition of different coatings on metallic substrate. Originality/value: The paper presents methodology of a non-destructive approach to determination of elastic properties and adhesion coefficient of coating materials with an overview of some applications already publish and also the new ones. Especially interesting are the results concerning the influence of surface preparation on adhesion coefficient which are published for the first time. Keywords: Coating materials; Elastic properties; Young’

Magnetic relaxation in iron based melt spun ribbons

In this paper magnetic relaxation processes in iron based amorphous alloys are examined in order to determine thermal/time instability of magnetic properties at room temperature. It was shown that the reversible component of magnetic relaxation in Fe74Cu1Cr3Si13B9 alloy can be well described by the coupling model usable for diffusion in strongly correlated systems. The proposed approach allows monitoring initial stages of structural relaxation

Magnetoimpedance effect in amorphous and nanocrystalline alloys based on iron

Purpose: The main purpose of the paper is to study magnetic, electrical and plastic properties of the selected group of amorphous alloys in the context of their application as magnetoimpedance sensors. Design/methodology/approach: The presented results were obtained by applying different magnetic methods (low field permeability measurements, magnetic relaxation, magnetization versus magnetic field, magnetization in saturation versus temperature, magnetoimpedance effect versus static magnetic field and/or frequency), resistivity versus temperature and Young’s modulus versus temperatures. Structural changes taking place in annealed samples were examined by making use of X-ray diffraction method and high resolution electron microscopy observations. Findings: It was shown that in all examined amorphous alloys soft magnetic properties can be enhanced by applying a suitable 1-h annealing at temperatures Top listed in Table 1. After annealing at this characteristic temperature magnetic permeability in relation to the as quenched state increases more than 20 times and non-contact magnetoimpedance effect (ΔZ/Z)ncmax is of the order of 104%. This effect can be explained based on the random anisotropy model supplemented by energy terms describing magnetoelastic energy and stabilization energy related to free volume content. For the alloys for which the optimized microstructure corresponds to the relaxed amorphous phase the plastic deformation corresponding to formation of brittle cracks is much higher than for the examined nanostructured alloys. In the frequency range from 700 kHz to 2 MHz magnetoimpedenace effect (ΔZ/Z)ncmax is approximately constant. Research limitations/implications: Searching of new soft magnetic materials in the group of amorphous alloys based on iron obtained by melt spinning can give a promising result. For example one can obtain very good soft magnets showing also good mechanical properties. Practical implications: Based on the presented results one can obtain very good soft magnetic material with low field relative magnetic permeability of about 16 000 (Fe74Cu1Zr3Si13B9). In the examined group of amorphous alloys the best candidate for magnetoimpedane sensor applications is the Fe75,75Ag0,25Nb2B22 alloy for which (ΔZ/Z)ncmax = 104% and plastic deformation εop=0.015. Silver as an alloying addition to the base Fe-Nb-B alloy significantly improves the alloy plasticity. Originality/value: It was shown that the examined amorphous alloys based on iron after applying a suitable thermal annealing can be used as promising materials for nagnetoimpedance sensors

Mossbauer temperature study of the Fe80Nb6B14 amorphous alloy

Temperature studies in the range 300−800 K of amorphous Fe80Nb6B14 alloy using Mössbauer spectroscopy are presented. It is shown that at a temperature close to 700 K iron clusters with non-collinear magnetic structure are formed. The observed magnetic permeability enhancement effect in the annealed at elevated temperatures alloy, which takes place in amorphous phase, is due to the strong ferromagnetic exchange between Fe clusters via the amorphous matrix and reduction of internal stresses

Application of the coupling model to magnetic after effects in the Fe72Co10Nb6B12 amorphous alloy

It was shown that magnetic reluctivity measured versus time after demagnetization for pre-annealed samples of the Fe72Co10Nb6B12 amorphous alloy exhibits highly non-exponential behavior which can be described by the coupling model. The relaxation intensity and the coupling parameter describing correlation effects in free volume diffusion decrease with increasing 1 h annealing temperature indicating annealing out of free volume and formation of iron clusters in amorphous matrix

Influence of transition and rare earth elements on magnetic properties of Fe-Nb-B-M (M = Ni, Ag, Gd, Tb) bulk nanocrystalline alloys

In this work we present magnetic properties of the (Fe80Nb6B14)1xMx (where M = Ni, Ag, Gd, Tb and x = 0:08, 0.16, 0.32) bulk nanocrystalline alloys prepared by making use of mould casting technique. The applied preparation technique is favorable to nanocrystallization of the alloys with mean diameters of crystallites ranged from about 10 nm to 30 nm. Phase identi cation reveals a formation of ternary RE2Fe14B and binary REFe2 phases dependently on the alloy composition. It was found that for the alloys with Ag addition magnetic moment of Fe atom increases from 2.26 B to 3.36 B for x = 0:08 and x = 0:32, respectively. For Ni addition this quantity decreases with increasing x due to appearing of Fe Ni (fcc) phases. For Gd, Tb additions the alloys are ferrimagnetic with compensation composition ranged between x = 0:08 and x = 0:16. The both rare earth alloying additions cause a signi cant magnetic hardening especially in the case of Tb

Magnetic properties of Co-Fe-Si-B microwires

In the paper the magneto-impedance effect in the Co68:15Fe4:35Si12:55B15 microwire with diameter of about 100 m is carefully studied. The measurements in close contact and contactless geometry were carried out in the static field ranging from 0 to 6 kA/m and frequencies of the alternating field from 20 Hz to 2 MHz. It is shown that the examined microwire shows high anisotropy of soft magnetic properties i.e. the circumferential permeability is at least 7 times higher than the longitudinal one. Moreover, the microwire can be used as highly sensitive magneto-impedance sensor working in contactless geometry especially at fields below 200 A/m[…

Preparation and magnetic characteristics of Co1−δZnδFe2O4 ferrite nanopowders

In the present paper the Co1 Zn Fe2O4 (0 1) ferrite nanopowders with a spinel type structure were synthesized using a chemical co-precipitation technique with constant flow rate FR = 120 cm3/min at three different reaction temperatures i.e. Tr = 50 C, 70 C and 90 C. Magnetic and structural characteristics of the obtained materials were investigated by means of X-ray diffraction method, transmission electron microscopy and vibrating sample magnetometer. In the course of studies hysteresis loops M( 0H) and the relations of magnetization M7T (determined at 0H = 7 T), squareness ratio S and the Néel temperature TN versus Zn content were determined and discussed in detail. It was shown that for < 0:6 the increase in reaction temperature Tr results in a significant increase of the measured magnetic characteristics. In particular, in the case of Co0:8Zn0:2Fe2O4 ferrite nanopowder magnetization M7T reaches maximal value of about 80 emu/g