Today, a large number of different sensors (for example, pressure and vibration sensors, as well as sonars) operate on the so-called magnetoelastic effect - a change in the magnetization of a metal product under the influence of an applied mechanical force in the elastic region of loading. For example, when you want to track the location of a submarine, an ultrasonic signal is sent through the water column and, reflected from the surface of the vessel, returns back in a slightly altered form. The sensor detects these changes, so it is possible to determine the location of the vessel.
In laboratory conditions, to evaluate the functional characteristics of materials for sensors, the effect opposite to magnetoelastic - magnetostrictive (change in the size of the sample under the influence of an applied magnetic field) is measured. The more magnetostriction the material possesses, the more opportunities the product receives from it. Among the “champions” are alloys of iron with gallium (Fe-Ga or gallophenols). In them, the change in the size of the sample reaches 0.04%, while in pure iron this figure is about 0.0015%.
Recently, scientific groups from the USA have shown that the best functional properties are shown by alloys with a nonequilibrium and heterogeneous structure, in which several phases with very close lattice parameters “adjoin” at once. This opens up new prospects for their application in the field of high-precision sensors, but the question remains: how to create and stabilize this nonequilibrium nanoheterogeneous structure so that it remains at ordinary temperature?
A team of scientists from the Department of Non-Ferrous Metals Metallurgy NUST “MISiS” together with specialists from the Joint Institute for Nuclear Research (Dubna) revealed a number of relationships between the temperature of processing of gallophenols and their crystal structure. These studies form a more complete picture of the processes taking place inside the crystal, which allows you to select the necessary processing conditions for the sample to stabilize the desired nonequilibrium structure. Scientists presented the results of the work in the form of a series of equilibrium and nonequilibrium phase diagrams, schemes of structural transformations of the crystal lattice. In addition, scientists have proved that alloying Fe-Ga alloys with microscopic doses of rare-earth elements can not only further increase their magnetostriction, but also stabilize metastable phases at room temperature.
“ Valeria Palacheva and Abdelkarim Mohamed , graduate students of NUST“ MISiS ”, began research on structural transformations in galfenols several years ago,
- comments project manager Professor Igor Golovin .
- An important stage in the research was the collaboration with the group of experimental physicist Professor Anatoly Balagurov from the Joint Institute for Nuclear Research. The goal of the joint (RNF) project is a systematic study of the structure and properties of iron-based alloys in a non-equilibrium state, including studies on a neutron reactor in combination with methods of physical metal science - scanning electron and transmission electron microscopy, X-ray, magnetometry, internal friction and others. "
Thanks to a systematic approach to studying the structure of gallophenols, scientists were able to establish under what conditions of heat treatment the alloys demonstrate their best functional properties.
The study is carried out under grants from the Russian Science Foundation. Further, the team plans to expand the field of research, using alloying with rare-earth metals more widely and using compounds of other metals with iron.