Laser alloying and cladding of metallic substrates

The paper describes the microstructure and properties (chemical composition and microhardness) of the surface laser alloyed layer with tantalum as well as coatings, made of Tribaloy T-400 and Stellite 6 powders, deposited by laser cladding. The surface alloyed zones varied in microstructure, zones depth and width, as well as Ta content related to the thickness of the coated layer, bonding paint type and the process parameters (power and scanning velocity). The electron microprobe analysis of melts showed that higher tantalum content in the melted zone resulted from the thicker original Ta coating as well as slower scanning velocity. Scanning electron microscopy examinations show that dendritic structure of the melted zone becomes evident when carbon was used as one of the components of the binder, while structure is typically martensitic when silicon-containing binder was used for powder deposition. Samples coveted with Ta and the carbon containing binder showed after laser alloying higher hardness than in case of using silicon-containing binder. Defect free coatings, made of Tribaloy T-400 and Stellite 6 powders, deposited by laser cladding on iron and nickel based substrates are described. The proper selection of the cladding process parameters permitted to get coatings with low dilution of the base material. Cross-sections of such coatings have been examined revealing their microstructure using optical, SEM and TEM electron microscopy, chemical (EDS microanalysis) and phase composition (RD), hardness and microhardness testing methods. As compared with other deposition techniques the microstructure of the laser coatings showed a high degree of refinement and chemical homogeneity. The grain coarsening was observed in the heat-affected zones and was explained as to be due to the overlapping of subsequent tracks during the coatings deposition. The erosive wear resistance of the coatings has been investigated. In general, the laser deposited coatings turned out to be susceptible for an extensive erosive wear. The effect was explained by lack of feasibility of the coated material to plastic deformation during erosion.