Discontinuous oxidation in wet air of T91 with a novel Al2O3-forming NiCrAl nanocomposite coating in as-deposited and pre-oxidized states

The 9 wt% Cr containing steel T91 was deposited with a Ni-16Cr-14Al nanocomposite coating by combining electrophoretic deposition and electrodeposition . After 500 h oxidation at 800 °C in 10 % H 2 O containing air, the bare T91 steel grew a triple-layered oxide scale consisting of an outer MnCr 2 O 4 layer, an intermediate Cr 2 O 3 layer and an inner SiO 2 layer. However, the nanocomposite-coated T91 grew an oxidation resistant oxide scale in the wet air, which was double-layered and consisted of outer NiAl 2 O 4 and inner α-Al 2 O 3 . Pre-oxidation at 1000 °C in dry air further reduced the oxidation rate of the coated T91, due to the formation of an exclusive α-Al 2 O 3 scale. The oxidation-resistant mechanism of the nanocomposite-coated steel without and with the pre-oxidation treatment was discussed. • An Al 2 O 3 -forming NiCrAl nanocomposite was coated onto T91. • The nanocomposite grew α-Al 2 O 3 at 800 °C in 10 % H 2 O containing air. • The nanocomposite coating increased the resistance of T91 to wet air oxidation. • Pre-oxidation at 1000 °C further helped the coating to resist the wet air oxidation.