High-temperature oxidation behavior of minor Hf doped NiAl alloy in dry and humid atmospheres

Oxidation behavior of NiAl and 0.05at.% Hf doped NiAl alloys were investigated at 1100°C in dry and humid atmospheres. Hf doping significantly improved the cyclic oxidation resistance. Water vapour promoted the formation of voids at the scale/alloy interface and accelerated scale spallation. Also, water vapour had effect on the phase transformation from θ- to α-Al₂O₃ at the initial oxidation stage. In humid atmosphere, more Hf segregated at the scale/alloy interface to form oxide pegs. Pre-oxidation process in O₂+Ar could compromise the effect of humid atmosphere on the oxidation kinetics of the NiAl alloys.