Structure Features of Surface Layers in Structural Steel after Laser-Plasma Alloying with 48(WC–W2 C) + 48Cr + 4Al Powder

Abstract

The article presents the results of studying the surface layers of structural steel samples alloyed with 48(WC–W2 C) + 48Cr + 4Al powder materials mixture using laser-plasma alloying technology. ROFIN-SINAR Nd:YAG-laser DY044 (Germany) with irradiation wave length λ = 1.06 μm was used for laser alloying. Equipment and technologies of laser-plasma alloying were developed at the E.O. Paton Electric Welding Institute. Detailed studies at all structural levels of grain, subgrain, dislocation structures, including phase precipitates and their stoichiometric composition, were carried out using optical, scanning electron, and microdiffraction transmission electron microscopy. It was found that the formation of crack concentrators in the treated surfaces is due to such structural factors as coarse-grained structure, chemical inhomogeneity, and the formation of dislocation density gradients in grain-boundary areas. Under the optimal mode of laser-plasma alloying of the treated surfaces, a fine-grained structure is formed with a uniform distribution of the dislocation density. In this case, the dislocation substructure is characterized by a cellular type with a cell size of 50…110 nm and by the presence of dispersed phase precipitates up to 100 nm in size in the internal volumes of grains. Dispersion of the structure, the formation of a non-disoriented cellular dislocation substructure with a uniform distribution of dislocation density, the presence of dispersed phase precipitates (nanoscale type) will contribute to an increase in crack resistance and strength characteristics due to substructural and dispersion hardening.