Effect of heat treatment on ordering and functional properties of the Fe–19Ga alloy

Abstract

Special attention in this work is paid to the study of the influence of cooling rates on microstructure and functional properties, magnetostrictive behavior and internal friction of polycrystalline Fe – 19 at.% Ga samples. After annealing at 900 and 1000°C for 40min, samples were water quenched (wq) or furnace cooled (fc). High resolution X-ray diffraction (XRD) exhibits the peak shoulder around 2θ=81° for the sample furnace-cooled from 900°C (fc900°C), which is ascribed to the formation of D03 ordered precipitates. Only a solid solution phase with an A2 structure is recorded in the samples water-quenched from 900°C (wq900°C) and 1000°C (wq1000°C). Annealing during 2h at 350°C of the water quenched from 900°C specimen (wqann) also leads to the formation of a shoulder around 2θ=81° due to the appearance of the D03 phase. Magnetic domain structure studied by magnetic force microscopy (MFM) reveals that the wq900°C sample exhibits a regularly aligned stripe domain structure, while irregular maze-like domain structure is observed in both the fc900°C, and wqann samples. Magnetostriction of the samples is measured as a function of an externally applied magnetic field. It was found that the wq1000°C sample comprises the highest magnetostriction, while the fc900°C and wqann samples have the lowest magnetostriction against the applied magnetic field; consequently, the damping capacity in wq samples is also the highest. Amplitude-, frequency- and temperature dependent internal friction tests of wq, fc, and annealed samples were carried out. Thermal history dependence of anelastic effects is analyzed on the basis of the A2→D03 transformation. Physical mechanisms for observed anelastic effects are discussed. Dilatometry and calorimetry studies are in agreement with the A2 (bcc)→D03 (bcc-based) ordering phenomenon at 200–300°C in as quenched samples.