No abstract

The authors explore the beads obtained by laser cladding with nickel-based self-fluxing alloy (grain size 20-80 μm) at different laser beam travel rates against the sample and different cladding distances. They examined the iron, nickel, chrome and silicon content of the coating in dependence on the cladding rate and the microstructure in each zone of a bead. As a result, it was established that the beads after laser cladding have a similar structure morphology in all the examined zones, which confirms that there is intense mixing of the molten-metal pool. A distinct correlation has been found between the distribution of coating elements and the modes of laser cladding: the nickel, chrome, and silicon contents of the coating are decreasing while the iron content is increasing with increased cladding rate. The authors point out a strong effect of radiation shielding caused by the vapours generated during the process of melting the powder particles in the area exposed to laser radiation.

No abstract

The paper considers improvement of physic-mechanical and operational properties of adhesive coatings after laser infusion with additional alloying В4С, ТаВ and МоВ. Influence of the laser infusion with additional alloying on structure, microhardness and wear-resistance of adhesive coatings of the Fe–Cr–B –Si system has been studied in the paper. While increasing a laser beam velocity microstructure is changed from equilibrium to quasi-eutectic. Presence of molybdenum boride and tantalum increases sensitivity of the coating to specific features of laser remelting. In both cases heat exchange conditions have been changed, a number of iron and chromium borides has been increased and due to this molybdenum and tantalum have been partially passing to free state that contributes to a disintegration of structural components. While introducing solid particles B4C into a coating they are dissolved in an iron matrix while being heated by a laser beam and under cooling they are isolated in the form of separated Fe an Cr boride inclusions. Laser infusion and alloying increase coating wear-resistance. Load increase from 30 to 70 Н improves coating wear resistance averagely by 15–26 % and wear resistance of non-alloyed coatings is improved by 26–43 %. An increase of melting rate and laser spot diameter does not exert significant influence on wear but an increase in overlapping coefficient leads to reduction of coating wear. Presence of solid particles in a coating and an increase in rate of melting by laser beam reduce coating wear resistance. Such rather complicated dependence of coating wear rate on conditions of laser melting and wearing process is due to a complex of structural and phase transformations which have contributed to formation of secondary solid inclusions and increased microhardness.