This review article analyses the results of experimental investigations of the influence of the cyclic direct γ−ε (f.c.c.-h.c.p.) and reverse ε−γ (h.c.p.-f.c.c.) martensitic transformations (MT) on the diffusion characteristics of Co atoms in Ã18Ñ2 (Fe-18.3 wt.% Mn-2.1 wt.% Si) alloy with low stacking-fault energy. With using of the radioactive isotopes via autoradiography and the layer analysis methods, it is shown the significant intensification of mobility of Co atoms by γ ↔ ε transformations is determined by two different independent mechanisms: due to the MT (athermal mechanism) and by means of the mechanism of thermal activation in the area of structural defects formed during the γ-ε and ε-γ transformations. The possibility of Co atom transport by means of the athermal mechanism in the process of cyclic martensitic transformations (CMT) by moving of interstitial atoms and their complexes along the close-packed (111) γ and (001) ε planes in the crystal lattices of f.c.c. austenite and h.c.p. martensite, respectively (crowdion mechanism) is analysed. The ability of the crowdion complexes to move with a velocity exceeding the velocity of sound in a crystal in the field of high internal stresses arising during high-rate deformation of austenite in a MT process is taken into account. The regularities of accumulation of such structural defects in the CMT process as disorientation of the crystal lattice and chaotic stacking faults (CSF) are investigated by the x-ray methods for the single-crystalline and polycrystalline samples. The intensification of diffusion processes in a phase-hardened alloy by the thermal-activation mechanism is attributed to the increase in the Co-atoms' mobility in the region of accumulation of defects in the crystal structure. An analysis of the regularities of accumulation of different types of defects with an increase in the phase-hardening degree made it possible to establish a certain sequence of their influence on the diffusion mobility

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Applying the x-ray, metallographic, and microdurometric methods, the phase composition and structural–stress state of the Fe-based alloys under the impact of electrospark treatment in combination with laser processing are studied and analysed. As shown, the structural–phase state of electrospark coating on the steel substrate is determined by several factors. They are the dissociation of WC carbide on the surface of alloying electrode on the W2C and W components followed by their erosion, an interaction of erosion products with elements of the interelectrode medium (C, N, O), an interdiffusion of the coating elements and a steel substrate, and the ascending diffusion of C from the substrate near-surface layers. As revealed, the heterophase coating and near-surface layers of substrate possess a complex structural–stress state. As shown, the residual stresses in different phase components have been formed through different regularities: the tensile stresses in the TiC-based compound, while the compressed stresses in the W2C, W, and Feα. The selective effect of laser heating of the coating on the stresses of different signs is revealed.