Corrosion behavior and mechanical properties of plasma sprayed Al₂O₃-aluminum bronze and Ca₂SiO₄-aluminum bronze coatings

NiCr-Al2O3-aluminum bronze (NAC) and NiCr-Ca2SiO4-aluminum bronze (NDC) coatings were prepared by atmospheric plasma spraying. Corrosion experiments were performed on coatings including immersion in simulated seawater and dry-wet composite salt spray test. Phase composition and microstructure of the coatings were investigated by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy, before and after the corrosion tests. The adhesion strength and hardness of coatings were also evaluated. As observed, Ca2SiO4 had much lower hardness than Al2O3 layer. Due to the rougher surface and higher thermal expansion of Ca2SiO4 layer, NDC coatings possessed better adhesion. Further, NDC coatings exhibited relatively superior corrosion resistance. According to the microstructure and phase analysis, this finding was attributed to the hydration reaction of Ca2SiO4 during the tests.