| The propeller is the main propulsion device for ships and because of the bad workingenvironment, it withstands sea water corrosion, biofouling, strong impact corrosion,cavitation corrosion and corrosion fatigue, thus greatly reduced its efficiency and servicelife. As the main material of propeller, the comprehensive performance of nickel-aluminumbronze is critical to the development of ships. As the nickel-aluminum bronze is usuallyused in the as cast condition, thus resulting in less understanding of the influence of heattreatment on microstructure and properties. On the other hand, with the development oftechnology of surface coating, surface treatment technology is widely used in metal’slong-lasting anti-corrosion, and has made gratifying achievements. In this paper, the OM,SEM, EDS and XRD, as well as the simulated seawater immersion test, electrochemicalpolarization curve test, cavitation corrosion test and mechanical test are used to explore themicrostructure, phase composition and corrosion resistance of the as cast and heat-treatednickel-aluminum bronze. The arc spraying technology is also used to make316L stainlesssteel coating on the surface of the nickel-aluminum bronze alloy, by measuring themechanical properties and corrosion mechanism of the coating, we explore the effect ofsurface treatment on the corrosion resistance of nickel aluminum bronze. The results showthat:The microstructure of as cast nickel-aluminum bronze includes α phase and phases.The phases distribut on α phase with different shapes. After immersion in artificialseawater for some time, there first appeares honeycomb porous corrosion productsgenerated on the surface of cast nickel-aluminum bronze, the inner layer of the corrosionproducts is oxide film which is thin and compact. After immersion for90D, there is thickpassive film generated on the surface, it is mainly Cu and Al oxides, it also contains Ni andFe oxides, CuCl and Cu2Cl (OH)3et al. The surface film reduces the corrosion rate of thesample. In the cavitation erosion test, the micro crack first formes at the junction of α phaseand phases, and then extends to α phase and makes weight loss. phases will then alsoremovs from the substrate. The important reason for the cast nickel-aluminum bronze tohave good anti-cavitation performance is that it has good work hardening ability and thealloy can effectively absorb the energy to its surface.After solution for2h at900℃, the microstructure of nickel-aluminum bronze isα++β’phase, then part of the β’phase will split into α+Ⅲphase if the aging temperature isbelow450℃and all β’ phase will split if the aging temperature reaches500℃. Aging hardening is obvious when aging time changes from300℃to450℃after solution at900℃of2h. The hardness reaches the peak when aging for1h and the phenomenon of aginghardening disappeared when aging temperature reaches and is above500℃. The microcracks first formed in the junction of α and β’ phase of the heat-treated nickel-aluminumbronze (900℃×2h+400℃×1h) and then α phase at the boundary removed from the surface.Because of the poor hardening capacity of the heat-treated nickel-aluminum bronze, it hasno buffer effect to the stress on the surface, so the metal removes from the matrix with largeblocks.316L stainless steel coating has typical lamellar morphology and the particle is fullydeformed. It is mainly mechanical bonding between the coating and the substrate and thereis no mutual diffusion of alloy elements. Some of the Fe element of316L stainless steelwire was oxidized to form Fe2O3(α) in the process of melting and impacting to thespecimen surface with high speed. The corrosion of the coating in artificial seawater isnot uniform corrosion, and the loose corrosion product is Fe2O3. The corrosion resistanceand anti cavitation ability of coating sample are lower than that of the as castnickel-aluminum bronze. |
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