I.S. Belashova - Dr.Sc. (Eng.), Professor, Technology of Construction Materials Department, Moscow State Automobile and Road Technical University (MADI). E-mail: irina455@inbox.ru
L.G. Petrova - Dr.Sc. (Eng.), Professor, Technology of Construction Materials Department, Moscow State Automobile and Road Technical University (MADI). E-mail: petrova_madi@mail.ru

In this paper we study the task of heat treatment of amorphous pyrolytic chromium coatings for implementation of controlled crystallization process with the release of nanoscale dispersed carbide particles . To do this, the effect of heat treatment of radiation and laser sources for heating chrome pyrolytic coatings produced at various modes of deposition were investigated. There were determined optimal regimes for coating structure, the most promising in terms of crystallization of the amorphous phase and the formation of nanocluster structures in further heat (laser or furnace ) treatment. Amorphous chromium coatings were prepared by precipitation from organometallic compounds of chromium on a substrate made of carbon and low-alloy tool steel. Studies have shown that the chemical composition of the substrate has no significant effect on the kinetics of deposition and structure of the resulting coatings. Their structure is determined by the deposition temperature interval. Three mechanisms of formation of coatings with different structures are realized and depend on the deposition temperature: kinetics, diffusion and transient. It is actually to research coatings in transition, emerging in the intermediate temperature range: coating is formed by alternately kinetic and diffusion mechanisms. The resulting coatings have a more complex structure and phase composition: in the deposition temperature range 450480oC there observed horizontally layered structure, which is an alternation of light layer, which is an amorphous phase, and dark  fine-grained chromium carbide layers. Annealing of the coatings obtained in the transient mode of deposition, allows to control crystallization of the amorphous phase, the particles of chromium carbide mixture at the same time are the centers of crystallization. For the formation of nanoscale crystal nuclei in the amorphous phase annealing at temperatures 540560oC is proposed. In this temperature range in coatings transient there is a violation of layering with the release of carbides and their conglomerates in some parts of the layer (Fig. 3a). After annealing, a coating thickness of 6 mm is formed , the transition zone of thickness 20 microns. X-ray analysis reported the presence of coherent links between the nanoparticles and amorphous solid solution. Thus, there is a precipitation hardening coating of chromium carbide nanoparticles coherently related to the amorphous solid solution, leading to a sharp increase in the microhardness  ... 27000 to 23000 MPa. There are more significant hardening of amorphous coatings, when the laser annealing using. Laser action is accompanied by the formation of a developed substructure, the dislocation density increases, the development of thermoplastic deformation and grinding grain, which involves additional reinforcing mechanisms, besides dispersion [5]. Thus, the experimental data show that high chrome microhardness of pyrolytic coatings is determined by their preparation technology, the degree of crystallization of the amorphous phase by annealing, and emphasizing excess of chromium carbides in the form of nanoparticles.