Preparation of thin NiCrBSi laser cladding layers with no microcracking and low dilution

To further extend the application of laser cladding, trials to prepare thin NiCrBSi layers by laser direct cladding were conducted using common Nd:YAG laser equipment in this study, and the influence of main processing parameters on the cladding quality and melting of the substrate was investigated. The results reveal that using coarse powder, solidification microcracks appear at the center of the melting pools, with some alloy drops on the as-cladded surface. After remelting, most of the drops can be melted, and the surface becomes flatter. When the laser pulse frequency is high enough, the microcracks can be completely eliminated by the next laser spot; then, a cladding layer of about 150 μm thick is obtained, while melting of the substrate and fusion between the cladding alloy and the substrate are still obvious. Using a finer powder that has a higher light absorption rate, thinner (∼100 μm) and uniform cladding layers with no microcracking can be obtained without remelting, and melting of the substrate is far less serious. All the thin cladding layers show much higher microhardness than the substrate, and the heat effect on the microstructure of the substrate is not obvious. High scanning speed, enough current, and short pulse width are suggested to get high quality thin cladding layers.