Processing of a low-cost γ–γ′ NiPtAl coating with improved oxidation resistance

A novel γ–γ′ (Ni solid solution—Ni₃Al) NiPtAl coating was produced on advanced single-crystal (SC) superalloy N5 by electroplating of a thin Pt coating with ~ 3 μm in thickness followed by heat treatment at 1000 °C in vacuum. For comparison, a traditional γ–γ′ NiPtAl coating was also produced by electroplating of a thick Pt coating with ~ 6 μm in thickness followed by heat treatment at 1100 °C in vacuum. The novel coating has a mass gain of ~ 0.5 mg·cm⁻² after 100 h 1-h cyclic oxidation at 1150 °C, showing better oxidation resistance than the traditional coating. An oxide scale mostly consisting of α-Al₂O₃ grew on the novel coating because the element Cr from the SC alloy substrate contributes to the formation of α-Al₂O₃. Pt content in the novel coating has significant effect on the oxidation resistance. The optimized Pt content in the coating is about 16 at%, which is helpful to reduce the diffusion of harmful elements from the substrate into the coating but also to reduce the cost of the coating.