Effect of electrode degradation on stability of nugget formation during small-scale resistance spot welding is presented in this paper. Production of spacer grids for nuclear fuel assemblies made of E110 zirconium alloy cells of 0.25 mm thickness was studied. The following degradation processes took place in the electrodes as they wore. Roughness of the tip surface was gradually reduced to the values of the welded cells. The semispherical tips were severely deformed during the initial period of their operation (1.500...2.000 welds). The deformation dynamics slowed down significantly after that. Microhardness on the tip surface of the electrodes decreased. It was minimal in the central part of the surface layer with a thickness of 50...100 μm and increased towards the periphery. Significant coarsening of the electrode metal microstructure occurred at a depth of ~ 1 mm. Nugget area and its tensile strength decreased as the electrodes wore. An increase in welding current did not reduce deterioration of nugget quality. Measurement and processing of dynamic resistance between electrodes did not make it impossible to predict and control the properties of nuggets for the studied welding modes.

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The paper presents the effect of irradiation of 321 steel substrates with a high-intense pulsed ion beam (HIPIB) on changes in functional properties of the surface layers and tribological characteristics of AlN coatings subsequently deposited above by the reactive magnetron sputtering method. The morphology of the modified surface layers, their microhardness and free surface energy levels are presented for different HIPIB energy densities. HIPIB irradiation of the substrates caused variations in the results of scratch tests combined with the acoustic emission signal processing. Their analysis has enabled concluding that the crack initiation threshold could be at least doubled for the studied coating/substrate system due to preliminary HIPIB irradiation. Finally, the obtained data were discussed, and future research directions were proposed.

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