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

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.