Cavitation erosion and corrosion behavior of Ni-Al intermetallic coatings

The high fracture toughness and corrosion resistance of Ni3Al intermetallic material produces good cavitation resistance. To yield Ni-Al coatings on commonly used metals is beneficial in many aspects. A cathodic arc plasma (CAP) ion plating process was demonstrated to deposit Ni-Al film on AISI 1045 carbon steel to evaluate the cavitation protection. Three target materials with Ni52Al48, Ni60Al40, and Ni70Al30 compositions were used to reveal the microstructural and compositional effects on cavitation erosion behaviors of coatings. Experimental results show that the nickel content in these deposits increased with the nickel content of the target material. The major phase of deposited film was Ni3Al regardless of the target materials. A nickel phase was produced if nickel-rich target Ni70Al30 was used. The scratch test indicated that all of the as-deposited films presented very strong adhesion. This reflects their cavitation erosion behavior in fresh water. All coatings increased the cavitation erosion resistance of the bare substrate 10-fold. These coatings also enhanced the cavitation resistance twofold or greater in 3.5 wt.% NaCl and threefold in 3.5 wt.% HCl electrolyte. The potentiodynamic polarization data of coated specimens in these two electrolytes indicated that the coated specimens exhibited higher corrosion potential and lower corrosion current density than the bare substrate material. It is believed that the cavitation erosion induced pitting corrosion into the substrate accelerated the mass loss rate of the substrate. (C) 2003 Elsevier Science B.V. All rights reserved.