Study On WC-Co Wear Composite Coating By Plasma Melt Injection

Production process, microstructure and wear properties of metal matrix wear composite coatings produced by plasma melt injection (PMI) were investigated.In this thesis, technology was applied to design engineering testing which was single factors fixed testing. The three factors included scanning velocity, powder flow and diameter of the nozzle of powder supplier. And particle size (20-40mesh and 300-400 mesh) was regarded as a factor to design monofactorial testing. XRD was applied to analysis coatings,optical microscope and SEM to observe microstructure,EDS for composition analysis,hardness to detect microhardness of layer and wear resistance tester to detect wear resistance of the coatings.The result shows that the appearance of specimen can be improved by raising scanning velocity at constant powder flow, and it also can be improved by raising powder flow at constant scanning velocity. Scanning velocity and powder flow both have notable influence on microstructure and the influence of powder flow is more powerful. The raising of scanning velocity contributes to formation of dendrite. The raising of powder flow contributes to no melted particle and formation of graphite. Particle size of WC-Co has distinct influence on the more no melted particle exist in the microstructure produced by PMI 20-40 mesh WC-Co particles.The coating and substrate integrate metallurgically and form three zones, namely coating, heat affected zone and substrate. There are no cracks but many porosities and bulky dendrite exist in the coating. There are many no melted WC particle in the WC-8C0 coatings. Microstructure is found in the plasma melt injection WC-8C0 coatings, which consists of no melted WC particle, WC,W₂C, M₆C(Co₃W₃C and Fe₃W₃C), martensit,pearlite, austenitic phases. Microstructure is found in the plasma melt injection WC-17Co coatings, which consists of no melted WC particle, WC,W₂C, M₆C(Co₃W₃C and Fe₃W₃C), martensit, austenitic phases and so on. The difference of microstructure in different zone of the WC-17Co coatings is obvious. It is easy to formation of graphite. Mechanism of wear of Q235 matrix is adhesion wear and abrasion wear. Mechanism of wear of the WC-8C0 coatings and the WC-17Co coating is abrasion wear.The wear resistance of the WC-8C0 coatings is 87.0 times as good as Q235 matrix. The wear resistance of the WC-17Co coatings is 14.2 times as good as Q235 matrix.