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The positive effect of plasma electrolytic treatment on CrWMn tool steel to increase the wear resistance of its surface is shown. The effect of plasma electrolytic nitriding and subsequent polishing on the structure, phase and elemental composition, microhardness of the surface layer, and surface morphology is established. Steel nitriding leads to the formation of a modified surface layer including Fe2–3N iron nitride and nitrogen martensite, below which hardening martensite is formed, reaching a microhardness value of 1200 HV. Subsequent polishing leads to a decrease in surface roughness by 42–68%. Tribological tests were carried out according to the shaft-bushing scheme. A decrease in the friction coefficient and weight wear of up to 2.6 and 30.1 times, respectively, is shown. The formed structure of the surface layer compensates for the effect of the counter body and determines the destruction of friction bonds by plastic displacement. The wear mechanism has been established and is defined as fatigue wear under dry friction and plastic contact. [ABSTRACT FROM AUTHOR]

Zr57Cu15Ni10Nb5 (more known as Vit-106) is a promising zirconium-based alloy with a high glass-forming ability, and belongs to the so-called bulk metallic glasses (BMG). Workpieces with a size of around one centimeter in all three dimensions can be obtained from a BMG alloy by casting. However, further increasing the cast size decreases the cooling rate and thus induces crystallization. Selective laser melting (SLM) is a well-known technique to overcome size limitations for BMGs because a workpiece is built by the addition of multiple melt portions in which the cooling rate is kept above the critical one. Currently, BMG parts obtained by SLM suffer from partial crystallization. The present work studies the influence of SLM process parameters on the partial crystallization of Vit-106 by metallography and the influence of the microstructure on mechanical properties by microhardness and wear resistance testing. Submicron crystalline inclusions are observed in an amorphous matrix of a Vit-106 alloy obtained by SLM. The size and the concentration of the inclusions can be controlled by varying the laser scanning speed. It is shown that submicron crystalline inclusions formed in the amorphous matrix during SLM can favorably affect microhardness and wear resistance. [ABSTRACT FROM AUTHOR]

The paper presents the results of optical diagnostics of evaporation and displacement of powder fractions during the formation of a single track in the process of selective laser melting. The velocity of the powder fractions is estimated. It was defined, that an increase in the scanning speed leads to an decrease in the particle coming out rate from the molten pool and the rate at which they are attracted. The results allow evaluating the kinetics of the mass-transfer process during selective laser melting. It was clearly shown the material quality properties after the selective laser melting are strongly influenced by the formed thermal field in the laser-irradiated zone.

Gas-phase flows occurring in a plume in a processing zone during selective laser melting (SLM) can significantly affect the quality of the process. To further enhance SLM performance, the characteristics of the flows should be considered. In this article, the vapor-gas jet emerging from the laser processing zone was studied. It was visualized by interferometry to evaluate flow velocity, geometry and changes in refractory index depending on laser power. The velocity and pressure fields of the vapor jet and the entrained ambient gas were estimated by mathematical modeling. It was shown that the increase of laser power led to higher jet velocity and greater change in its refractory index. The latter also was used to evaluate the content of metal vapor in the plume and its influence on the absorption of laser radiation. [ABSTRACT FROM AUTHOR]