Preparation and characterization of NiCrAlY/nano-YSZ/PCL composite coatings obtained by combination of atmospheric plasma spraying and dip coating on Mg-Ca alloy

A triple-layer NiCrAlY/nano-yttria stabilized zirconia (nano-YSZ)/polycaprolactone (PCL) coating was deposited on Mg-Ca alloy by novel combination of atmospheric plasma spraying (APS) and dip coating methods, aiming at further enhancement of the corrosion and mechanical properties of the Mg alloy. The compressive strength of the triple-layer plasma/polymer coating is higher than that of the plasma coated and uncoated samples after immersion in 3.5 wt% NaCL solution. However, both single and dual-layer plasma coatings demonstrated better bonding strength than the triple-layer plasma/polymer coating. The corrosion resistance of Mg alloy was significantly improved by triple-layer NiCrAlY/nano-YSZ/PCL coating this was inferred from the lower corrosion current; 0.14 mu A/cm(2) versus 285.3 mu A/cm(2) for the uncoated Mg alloy, the higher corrosion potential; -1252.8 versus -1631.4 mV(SCE), and the significantly lower corrosion rate; 0.003 versus 6.51 mm/yr. A corrosion mechanism for the single-, double- and triple-layer coated Mg alloy was proposed. PCL coating provides significant protection for the Mg alloy by sealing the porous nano-YSZ plasma coating. (C) 2015 Elsevier B.V. All rights reserved.