The presented approach is based on experimental observations which clearly show that the hot cracking phenomenon is a result of accumulation of macroscopic tensile strains in a microscopic intergranular film of liquid enriched with segregating elements at the final stage of solidification. The modeling takes into account the effects of strain accumulation as well as the influence of the microstructure and the thermo-dynamical properties of the welded material. The integrated approach provides a clear phenomenological interrelation between parameters of the welding process, properties of the welded material and the cracking susceptibility. It is successfully used for the development of technological means, such as a multibeam welding, for eliminating solidification cracking.

Cobalt oxide based nanostructures are perspective materials for gas sensors, photocatalysts, and other devices for ecology applications due to the high concentration of chemisorbed oxygen and catalytic activity in oxidation reactions. Finely dispersed nanocrystalline oxides Zn x Co3–x O4 (0 ≤ x ≤ 1) with a high level of conductivity have been synthesized by the chemical precipitation of oxalates with subsequent thermal treatment. Comprehensive studies of the morphology, electrophysical properties, nature and concentration of defects in the obtained materials were carried out. It is shown that the introduction of zinc atoms to the Co3O4 structure leads to a sharp increase in conductivity by more than 5 orders of magnitude. In addition, the zinc-induced interplay of Co2+ spin centers between tetrahedral and octahedral sites was revealed using the EPR method. The correlation between the conductivity and the concentration of Co2+ ions in tetrahedral and octahedral environments was established for the first time. The obtained results open up the possibility of fine-tuning the electronic properties of nanostructured Zn x Co3–x O4 by variation of zinc concentration in the samples.

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