Microstructure and properties of NiCrBSiC overlay coatings deposited by the plasma scanning process

NiCrBSiC coatings on S275JR non-alloy structural steel substrate were produced using the plasma transferred arc (PTA) scanning process. Coatings were carried out by a preplaced powder method using a mixture of NiCrBSiC powder and a binder, painted over the substrate. The thickness of the coatings ranged from 1 to 2.5 mm due to the use of three different current densities (50, 65 and 80 A). Layers were produced under Ar atmosphere and cooled in air. Microstructural characterization studies were carried out by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurements. They revealed the presence of a γ-Ni solid solution dendritic phase and interdendritic precipitates, which were found to be Ni3B and Cr23C6 particles. It is determined that the thickness of the coating layer increases with the current density and the concentration of the alloying elements decreases. Coatings are homogenous and no cracks or pores were detected in the interface. The hardness of layers varies in the range of 400–1800 HK.