Preparation And Optimization Of Ni-based Coating Based On The Corrosion Of Propeller Blades

As for mechanical parts,surface engineering is one of the important means of improving the performance in complex working conditions.Brass is the based material on existing Marine propeller blades.Dezincification restricts the service life although brass with superior properties.Preparation of appropriate protective layer is a feasible means of extending the service life.The paper focuses on electroless Ni-based coatings.Meanwhile,the effect of X element and re-melting on coatings were researched.SEM/EDS/XPS/XRD and EPMA were used to study the microstructure and morphologies.Electrochemical workstation/micro-hardness testing device/friction wear testing machine and erosion equipment were applied to research mechanical properties of those coatings.Based on the material of existing Marine propeller blades,different corrosion and dezincification mechanism existed in different solutions.The corrosion products in these three solutions are complicated.Except for the CuO and ZnO,some specific products exist in these systems:Cu₂O and ZnSO₄ in H₂SO₄ system,Cu₂O and Zn?OH?₂ in NaCl system,Cu?OH?₂and a large quantity of Zn?OH?₂ in NaOH system.According to the cathodic polarization curves,corrosion mechanism of HSn62-1 in H₂SO₄ solution is controlled by both hydrogen evolution and oxygen reactions but the latter is primary reaction.Further,in NaCl solution is controlled by hydrogen evolution and in NaOH solution is controlled by oxygen reactions.The different effect of doping W,WC,Cr,and Al2O3 on the microstructure,crystallinity and mechanical properties of Ni-P-X coatings has been investigated.The doped coating Ni-P-Al₂O₃ and Ni-Co-P show excellent properties.Furthermore,Ni-Co-P/Ni-P muti-layer coating shows superior cohesion.Re-melting testing on low-phosphorous coating?Ni-8%P?suggested that it contributs to improving corrosion resistance,hardness and wear-resistant but went against to erosion property.Compared to non-phosphorous?Ni-Co?coating,it implied that the significance of P was forming Ni₃P interstitial solid solution,thus improving the strength of Ni-based coatings.