Influence of point defects and grains size on the course of reversible martensite transformation in melt spun ribbons of the copper based alloys

Purpose: In the paper Cu-Al-Ni-(Mn, Ti) alloys exhibiting the shape memory effect were studied. For the investigated alloys the characteristic temperatures of the reversible martensitic transformation, the influence of grains size and vacancy concentration on the course of the transformation were examined. Design/methodology/approach: Using the resistometric method it was shown that the characteristic temperatures of the reversible martensite transformation strongly depend on the grains size. Findings: For Cu-Al-Ni alloy the activation energy of migration of monovacancies and the pre-exponential factor of the Arrhenius equation were determined as =(0.7±0.1)eV, Ko=1.7·10 º8.0±0.3s-1, respectively. Practical implications: The paper shows that the investigated alloys can be used as important functional or the so-called intelligent materials (actuators, sensors). Originality/value: The parameters of the electronic structure - i.e. the coefficient of conduction electron scattering at grain boundaries, the mean free path, the coefficient of reflection of conduction electrons at grain boundaries, and the electrical resistivity for Cu-Al-Ni in the martensite and parent phase were determined

Investigation of material properties by means of magnetic methods

In the present paper, magnetic method of determination of ferrite content in austenite steels, based on saturation polarisation and magnetic polarisation of ferrite near the remanence point, have been presented for Fe-Cr-Ni-type alloys. Magnetic phase analysis, taking into occount the distribution of total magnetic losses on eddy current losses, relaxation losses and hysteresis losses, have been discussed for low-carbon and low-alloy steels. The formulas on tangent angle of eddy current, hysteresis and relaxation (additional) losses have been presented. General formulas for magnetic permeability and coercive force have also been presented in terms of internal magnetic and material parameters. These parameters allowed to analyse the structural changes in magnetic materials. Examples of the influence of chemical composition, structural defects and thermal annealing on the changes of saturation polarisation, magnetic permeability, coercive force, magnetic hysteresis and relaxation losses have been discussed for low-carbon steels and amorphous alloys

Analysis of the nanocrystalline phase formation process in amorphous Fe-X-Si-B alloys

The process of nanocrystalline phase formation, affecting magnetic properties, in amorphous Fe78Si8 Bι4, Fe76 ΑI2 Si8 Β14 , Fe76 Cr2 Si8 B14 and Fe76 Mo2 Si8 B14 alloys has been studied in the paper. Investigations have been carried out using the electrical resistivity method, magnetic methods, transmission electron microscopy and X-ray diffraction. A nanocrystalline phase in the amorphous matrix has been obtained by isochronous or isothermal vacuum annealing. Phase composition of samples has been determined directly after manufacturing and after crystallization annealing on the basis of X-ray diffraction and electron diffraction. Transmission electron microscopy was used to determine phase morphology, dimensions of formed nanocrystalline phase and transition phase. Alloying elements have been found to affect changes of magnetic properties in amorphous and nanocrystalline states. For Fe76Mo2 Si8 Β14 alloys a significant increase in crystallization temperature, making difficult nanocrystalline phase growth and increase in thermal stability of magnetic permeability have been observed

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

Structural relaxation in Fe78Nb2B20 amorphous alloy studied by Mossbauer Spectroscopy

It was shown that soft magnetic properties of Fe78Nb2B20 amorphous alloy can be significantly improved by applying 1-h annealing at temperature 623 K (permeability increases even about 8 times). The Mössbauer Spectroscopy technique indicated that the optimized microstructure (corresponding to the maximum magnetic permeability) is free of iron nanograins and should be attributed to annealing out of free volume and a reduction of internal stresses i.e. to the relaxed amorphous phase

Magnetic properties of Fe76X2Si8B14 (X= Al, Cr, Mo) amorphous alloys

Purpose: The idea of the paper is to study the influence of thermal annealing and alloying additions on magnetic properties, optimization and crystallization processes in Fe76X2Si8B14 (X=Al, Cr, Mo) amorphous alloys. Design/methodology/approach: For annealed samples (1 h, Ta ranging from 300 K to 800 K) at room temperature magnetic permeability was measured by applying Maxwell-Wien bridge (frequency about 1030 Hz and magnetic field H=0.5 A/m). Magnetostriction coefficients – parallel and perpendicular were determined by applying infra-red magneto-dilatometer. Magnetization in saturation versus temperature was measured by making use of magnetic balance (field 0.5 T). Findings: It was shown that alloying additions in the examined alloys cause a decrease of the Curie temperature, an increase of magnetic permeability and magnetization in saturation. The observed ESMP (enhancement of soft magnetic properties) effect in the examined alloys can be attributed to the so-called relaxed amorphous phase free iron nanograins. It was shown that parallel and perpendicular magnetostriction coefficients depend on annealing temperatures which means that these quantities are sensitive on free volume content. Research limitations/implications: The obtained results are a part of a broad area of examinations devoted to establishing of the influence of different alloying additions and thermal annealing on soft magnetic properties of amorphous alloys obtained by melt spinning technique. Practical implications: The examined alloys belong to a modern group of soft magnetic materials, which can be used as core transformers, magnetic sensors, shields of magnetic etc. The obtained results may be used for preparing soft magnetic ribbons for specific applications. Originality/value: The originality of the paper lies in examination of the influence of free volume content on magnetostriction coefficients

Magnetic and mechanical properties in FeXSiB (X=Cu, Zr, Co) amorphous alloys

Purpose: The idea of the paper is to study the influence of different alloying additions (Cu, Zr, Nb) on structural relaxation, crystallization, and improvement of soft magnetic properties in amorphous alloys of the type FeXSiB obtained by melt spinning technique. Design/methodology/approach: Magnetic and electric characteristics of the as quenched and successively annealed samples were determined at room temperature. Experiments were carried out by applying magnetic permeability measurements (Maxwell-Wien bridge), magnetic after effects, resistivity (four points probe), magnetostriction coefficient (infrared optical sensor) and magnetization (magnetic balance and fluxmeter). Findings: It was shown that soft magnetic properties of the examined alloys can be optimized by applying 1-h annealing at a specific temperature. The process of the improvement of soft magnetic properties is found to be diffusion controlled. The Arrhenius parameters of this process were determined by applying magnetic measurements. Research limitations/implications: The obtained results are a part of a broad area of examinations devoted to establishing of the influence of different alloying additions and thermal annealing on soft magnetic properties of amorphous alloys obtained by melt spinning technique. Practical implications: The examined alloys belong to a modern group of soft magnetic materials, which can be used as core transformers, magnetic sensors, shields of magnetic, electric and electromagnetic fields etc. The obtained results may be used for preparing soft magnetic ribbons for specific applications. Originality/value: The originality of the paper lies in examination of the improvement of soft magnetic properties effect as a diffusion-controlled process. The influence of different alloying additions on the course of this process is well established

Structural Relaxation and Crystallisation in Fe-Cr-Si-B and Fe-Cu-Cr-Si-B Amorphous Alloys

Structural relaxation, crystallisation and optimisation processes in soft magnetic amorphous alloys based on iron are examined by applying different experimental techniques: X -ray diffraction analysis, high- resolution electron microscopy, measurements of magnetic and electric properties (permeability, after- effect, resistivity) . The presented results are discussed in terms of annealing out of micro voids, formation of a nano crystalline phase and changes of effective magnetostriction constant

Optimization of Soft Magnetic Properties in Fe-B and Fe-B-Si Amorphous Alloys Obtained by Melt Spinning Method

In the present paper the process of optimization of soft magnetic properties have been studied by applying different experimental techni ques (magnetic measurements, electric measurements, X -ray analysis, and high-resolution electron microscopy observations ). It has been shown that an increase in magnetic permeability after optimizati on annealing can be mainly attributed to annealing out of micro voids