Study On Microstructure And Properties Of Laser Cladding Ni-based WC Compsite Catings

In the light of the high cracking sensitivity and lacking of special powders in lasercladding, firstly in this study, the microstructure causes of laser clad layer's high crackingsensitivity were investigated by using experiments combining relevant theories. Secondly,special Ni-based WC powders for laser cladding were designed and two kinds of powders,SD-Ni45 and SD-Ni55, which had excellent performances, such as well crack resistance andgood formation property in laser cladding, were obtained. Finally, the microstructure, wearand corrosion behaviors of clad layers made by the non-optimized Ni-based WC powder andthe optimized powders SD-Ni45 and SD-Ni55 were analysed in detail.Results showed that at the same processing parameters, the highest non-cracking laserscanning speed for SD-Ni45 and SD-Ni55 laser clad layers were much higher than that ofNi-coated 20% WC clad layer, which proved their better anti-cracking performance. Analysisshowed that the cracks in Ni-based WC laser clad layer initiated at the sub-surface area andextended to the surface and bonding line, seperately, and stoped at the bonding line due to thecompression stress existing in the heat affacted zone (HAZ). The cracks of Ni-based WC cladlayer belonged to quasi-cleavage crack caused by low plasticity and high stress, including asmall amount of cleavage crack area.The microstructure of SD-Ni45 and SD-Ni55 clad layers had better microstructurehomogenity than that of Ni-coated 20% WC clad layer. It was found thatγ-(Ni,Fe), WC,α-W2C, FeNi3 and Fe3C existed in all of the three clad layers. Moreover, CrB, Fe3W3C, Fe2B,Fe3Si, (Cr,Ni,Fe,W)23C6, (Ni,Cr,Fe)7C3 were also found in Ni-based 20%WC and SD-Ni55'sclad layers, with different proportions and morphologies of the phases in the two clad layers.The excellent anti-cracking performance of SD-Ni45 clad layer mainly resulted from itshomogeneous and simple microstructure, while that of SD-Ni55 mainly resulted from that theformation of CrB reduced the content of low melting point eutectics such as Ni₃B, Fe₂B,etc. The surface macrohardness of Ni-based WC, SD-Ni45 and SD-Ni55 clad layer wereseperately HRC53, HRC45 and HRC55. The wear surface of Ni-based WC clad layer wasrough, with a large amount of adhesive traces, but very few scratchs. The wear surface ofSD-Ni45 clad layer was flatter than that of Ni-based WC clad layer, apart from some distinctscratchs and traces of primary phases. The wear surface of SD-Ni55 clad layer flatest of thethree clad layer, with the best anti-wear performance.The SD-Ni45 clad layer's equilibrium potential decreased a little compared with that ofNi-based WC clad layer, but its corrosion current was less than 25% of that of Ni-based WCclad layer, which meant that its corrosion resistance was more than 4 times of that of Ni-basedWC clad layer. However, for SD-Ni55 clad layer, its equilibrium potential increased 44.2%compared with that of Ni-based WC clad layer, and its corrosion current was less than 10% ofthat of the latter, which meant that compared with the latter, SD-Ni55 clad layer had not justlower corrosion tendency, but 10 more times of corrosion resistance.