Considered are the technologies of laser and laser-microplasma alloying of surface layers of 38KhN3MFA structural steel specimens with introduction of powder filler materials based on tungsten and chromium carbide, promoting increase of physical-chemical properties of the parts, manufactured from these steels. Structural transformations, concentration variations and reasons of crack formation in treated surface layers were investigated at different modes of alloying using the methods of light microscopy and analytic scanning electron microscopy. It is shown that susceptibility to crack formation in laser and laser-microplasma alloying of specimens of 38KhN3MFA steel is caused, first of all, by structural (size of crystalline particles, coefficient of their shape) and concentration variations, related with redistribution of the elements, in particular, chromium, that results in formation of grain boundary concentration gradients. Absence of microcracks in a fusion zone at laser-microplasma method of alloying allows making a conclusion about perspective of application of this method for surface treatment of parts, manufactured from 38KhN3MFA steel. 6 Ref., 9 Figures.

The problem of effect of solidification rate on structure of weld metal of scandium-containing aluminium alloys is considered. Peculiarities of scandium precipitation from melt in solidification of aluminium alloys under non-equilibrium conditions, simulating fusion welding, are investigated. Procedure of investigations has been developed and confirmed experimentally. Advantage of offered procedure over the existing ones consists in the fact that it allows simulate almost all the methods of fusion, from argon arc non-consumable electrode welding to electron beam welding. It is shown that the procedure satisfies the put aims completely. Microstructural investigations of ingots in height showed that within the interval of solidification rates from 10 3.3 to 10 2.5 °C/s the change of form of solidification occurs from dendritic to subdendritic ones. It was found that at rates of solidification, commensurable with solidification of weld metal, up to 0.41 % Sc can be contained in solid solution of alloys. When applying the highly concentrated power sources, such as electron beam, it is possible to reach the similar value also in welds. In arc methods of welding approximately 0.3 % Sc can be assimilated in solid solution of weld metal. It was found that it is necessary to provide its content in weld metal at the level of 0.35-0.40 wt.% to maximization of effect from alloying of welds with scandium. In this case the increase in mechanical properties of weld metal is provided both by refining of its crystalline structure, and also by hardening the solid solution by scandium. 7 Ref., 3 Tables, 4 Figures.

An essential difference in formation of structural-phase state at application of different welding conditions-friction stir welding compared to argon-arc welding-is considered in the case of welded joints of complex aluminium-lithium alloys. The urgency of comprehensive experimental-analytical assessment of interrelation of welded joint structure and properties is also shown. Assessments of specific contribution of structural-phase state (chemical composition, phase dimensions, grain, subgrain and dislocation structure) into the change of the main service properties of welded joints made by argon-arc welding and friction stir welding are considered, as well as the influence of welded joint structural state on the nature of distribution, level of growing internal stresses and their relaxation mechanisms under specific welding conditions. 10 Ref., 5 Figures.

The results of investigations of structural-phase conditions in surface layers of structural steel 38KhN3MFA and their changes under different modes of strengthening by laser and laser-plasma alloying are given. Experimental investigations were used as a basis for analytical evaluation of differential input of all structures being formed in strengthening and their parameters (chemical composition, grain and subgrain structures, dislocation density, volume fraction of phase precipitates etc.) in change of strength characteristics of alloyed layers, conditions of crack formation promoted by formation of local internal stress concentrators, i.e. zones of nucleation and propagation of cracks, as well as mechanisms for relaxation of such type of stresses. 12 Ref., 6 Figures.

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