Effect of thermal cycling on protective properties of alumina scale grown on thin Haynes 214 foil

The isothermal and cyclic oxidation of a thin alloy 214 foil (130 μm thick) has been studied in air at 1200 °C for up to 720 h. Haynes 214 forms a duplex oxide scale consisting of pure, columnar alumina overlaid by mixed Ni(Al,Cr)2O4 spinel with minor inclusions of (Al,Cr)2O3. A transition from external alumina to chromia scaling (abbreviated as TACS) occurs at the oxide-alloy interface after the Al reservoir of the foil is exhausted due to oxidation. The tensile cracking of the oxide scale upon thermal cycling is shown to promote the early transition from protective to accelerated breakaway oxidation.