Microstructure evolution and growth control of ceramic particles in wide-band laser clad Ni60/WC composite coatings

Nickel based composite coatings reinforced with WC particles were fabricated on substrate of Q550 steel utilizing wide-band laser cladding technology. To control the microstructure evolution and growth behavior of ceramic particles, different laser power was applied in manufacturing process. The microstructure characteristics were examined by optical microscope (OM) and field emission scanning electron microscopy (FE-SEM). X-ray diffraction (XRD) was applied to analyze the phase constitution of composite coatings. The wear resistance was examined by dry sliding tests utilizing MM2000 abrasion testing machine. The results showed that the added WC particles was partly dissolved and reacted with the molten Ni60 powders. Special cored-eutectic structure was formed at the top region of coatings, consisting of the inner boride ceramic and the fine lamellar eutectic around. Combining the XRD results with EDS analysis, the ceramic were confirmed as W2B5 and the eutectics were a mixture of (Cr, W)(23)C-6 and gamma-Ni(Fe). Adjustment of wide-band laser power had great influence on the growth behavior of the cored-eutectic structure. Due to the greatly refined ceramic-eutectic structure, composite coatings with laser power P = 3.6 kW exhibited excellent wear resistance which was about 6.8 times that of substrate steel. (C) 2015 Elsevier Ltd. All rights reserved.