High power diode laser cladding of Fe-Co-B-Si-C-Nb amorphous coating: Layered microstructure and properties

Fe-Co-B-Si-C-Nb amorphous composite coating about 0.6 mm in thickness was fabricated by using a one-step laser cladding method. Microstructures and phases were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electron probe microanalysis. Microhardness and wear resistance tests were conducted to evaluate the mechanical properties of this coating. Near the interface of coating/substrate, the region showed a layered microstructure, which could be generally categorized into three layers: layer I (columnar dendrites phase), layer II (equiaxed dendrites phase) and layer III (amorphous-particle composite phase). The main reason for this layered structure was due to the difference in chemical compositions of the three layers. With regard to mechanical properties, the microhardness and wear resistance of the Fe-Co-B-Si-C-Nb amorphous composite coating also exhibited layered characteristics. The mean value of the microhardness for layer I, layer II and layer III was 729, 680 and 1245 HV, respectively. The friction coefficient of the transitional layer III was 0.28 times lower than that of the substrate under the same sliding friction condition.