Abstract: The surface hardening of high-hardness and microporous small parts is difficult owing to its special structure characteristics. The valve seat, as a representative of such small parts, is hardened by laser fine cladding Cobalt-based alloy coatings by using the auxiliary processing device and the co-axial powder feeding system. The macromorphology, microstructures and microhardness are characterized by using laser microscope, SEM, XRD and microhardness tester . Comparison tests of service lives of the laser cladding specimens and the uncladding specimens are carried out on the fuel injection test rig. The results show that the phenomena of ablation and high tempering of the valve seat during the process of cladding are avoided while good forming of clad layer is ensured by using the pure copper auxiliary processing device . The problem of micropores blocked by cladding layer is solved by the method of inlaying kryptols. The laser cladding layer is comprised of a hypoeutectic structure, which contains primary dendrites and interdendritic eutectics. The primary phases are γ-Co, CoCx, Cr23C6, W5Si3 and etc. The metallurgical bonding forms well between the cladding layer and the matrix of GCr15 steel. Compared with the uncladding specimens, the erosion resistance of the laser cladding specimens is increased by 40%.

Key words: Cobalt-based, Erosion resistance, Laser cladding, Micropore, Microstructure, Small parts