Characteristic behaviours of clad layer by a multi-layer laser cladding with powder mixture of Stellite-6 and tungsten carbide

The powder mixture of Stellite-6 and tungsten carbide (WC) in the range of 0 wt.%–47 wt.% WC fraction with constant chemical composition multi-layer cladding (CCCMLC) and functionally gradient material multi-layer cladding (FGMMLC) were deposited on mild steel (JIS-SM400B) plates by a 2.4 kW cw CO2 laser. In the CCCMLC, the WC weight fractions at each layer are constant. In the FGMMLC, the WC weight fractions at each layer are varied by controlling the disk rotation speed of the feeder. The phase constitution, microstructure, hardness and wear resistance of the clad layer were investigated by an X-ray diffractometer, energy dispersion spectroscopy (EDS), scanning electron microscope (SEM), laser microscope, Vickers hardness tester and wear tester. According to the analyzed results, the microstructure of the clad layer consists of hypoeutectic structure, and undissolved tungsten carbides dispersed in the matrix of the Co-based alloy. The Vickers hardness increases with the increase of WC weight fraction. The clad layers of CCCMLC and FGMMLC have almost same wear resistance. On the other hand, to decrease the crack sensitivity of clad layer, the influence of a preheating temperature and WC weight fraction in the CCCMLC and FGMMLC on the crack sensitivity was investigated comparatively. As the result, the cracks of clad layer clad with the powder mixture of Stellite-6 and WC belonged to a quasi-cleavage fracture type crack. In the FGMMLC method with gradual increase of WC particles clad at three subsequent layers shifts the critical amount of WC at which cracking appears to the higher level, or that it reduces the required preheating temperature. Namely, the crack sensitivity of clad layer using FGMMLC method is lower than that of CCCMLC method.