Thermal stability of strains induced in Fe$_{81}$Si$_6$Nb$_3$B$_9$Cu$_1$ alloy nanocrystals during annealing under tensile loading

The effect of nanocrystallization annealing under tensile loading on residual strains of nanocrystals in the soft magnetic alloy FeSiNbCuB (Finemet) has been investigated using X-ray diffraction. It has been shown that the body-centered cubic lattice of $\alpha$-FeSi nanocrystals is extended along the direction of the application of the load upon annealing and is compressed in the transverse direction. It has been established that the extension of the lattice along the crystallographic axes coinciding with the stretching direction as well as the compression in transverse directions are well described within the framework of the elastic strain theory taking into account the symmetry of the cubic lattice. The isotropic and anisotropic Poisson’s ratios of nanocrystals have been determined. The thermal stability of the strains of nanocrystals has been analyzed. The annealing without external influences leads to a decrease in the strain and the Poisson’s ratio.