Long-Term Corrosion Behavior of Atmospheric Plasma Sprayed NiCr Alloy Containing Boron in 3.5 wt.% NaCl Solution

Abstract

Since the plasma sprayed coatings always present a limited interlamellar bonding, it is difficult for a plasma sprayed coating to be applied in corrosion environment without any post-spray treatment. In this study, a NiCr powder alloyed with boron was employed to fabricate fully dense corrosionresistant coating by plasma spraying through in-situ deoxidation effect of boron. As reported previously, plasma sprayed Ni20Cr4B coating presents fully dense microstructure with few isolated pores. Due to the oxide-free state of the inflight particles by the deoxidation effect of boron, the splats were effectively bonded upon impact so that the inter-splat boundaries were indiscernible. A long-term immersion corrosion test in NaCl solution was conducted for 80 days to confirm that the plasma sprayed Ni20Cr4B coating presents the superior resistance against the corrosion, which was comparable to the flame spray-fused NiCrBSi coating. Furthermore, the cross-sectional microstructure of the Ni20Cr4B coated Al alloy samples after 80 days immersion revealed that the plasma sprayed Ni20Cr4B coating was dense enough to completely block the penetration of corrosive substance in such an aqueous corrosion environment.