Abstract
As a new surface modification technology, laser cladding has been widely used in the area of parts manufacturing and repair because it can produce cladding layer with good performance. The metal-ceramic composite coating produced by laser cladding can provide well adjacent to the substrate and can service in extremely severe working conditions.In this paper, cobalt-base alloys with WC powder as cladding materials cladded on the substrate of 304 stainless steel by Co2 laser and lateral powder feeding device was prepared into laser cladding composite coating. The influence of laser technical parameter and WC content on the morphology、microstrcture、properties of cladding layer were discussed. The microstructure、component distribution and phase composition of cladding layer were analysed in detail through optical microsocopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS)and X-ray diffraction (XRD). The hardness and its distribution of cladding layer was tested by Vickers hardness tester.The wear resistance of cladding layer with different content WC were tested by abrasion testing machine.
The experiment results showed that with increasing the laser power, the dilution rate of cladding layer increased, the hardness first increased and then decreased. With increasing the scanning speed, the structure of cladding layer became finer, the hardness first increased and then decreased. When the laser power was too high or the scanning speed was too slow, the cladding layer would be overheated, conversely, the surface of cladding layer was coarse, the internal combination was poor. When WC content increased gradually, the solidification characteristic of cladding layer changed from hypoeutectic to hypereutectic finally, and the dilution rate of the cladding layer gradually increased. The
phase composition of cladding layer with 0%WC was γ-Co、M7C3、CoCx and W2C, with 20%WC was γ-Co、M23C6、CoCx、M7C3、Co3W3C6、W2C and WC, with 50%WC was γ-Co、M23C6、CoCx、M7C3、Co3W3C、Co6W6C、Fe6W6C、WC and W2C. The hardness of cladding layer increased with increasing of WC content, when WC content was 60%,the hardness of upper cladding layer could reach above 1200Hv. Wear resistance of cladding layer increased with increasing of WC content. When the WC content was up to 50%, cladding layer had the best wear resistance. However, When WC content increased to 60%, the wear resistance of cladding layer decreased slightly. The study showed that the root cause of cracking in cladding layer was stress, cracks in cladding layer was belong to cold cracks. With increasing of WC content, the crack sensitivity of cladding layer increased. The crack sensitivity of cladding layer could be reduced effectively by preheating the substrate.
Key Words: laser cladding, cobalt-base alloys, microstructure, hardness,wear resistance
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