A TEM study of the oxide scale development in Ni–Cr–Al alloys

A study was undertaken to investigate the isothermal oxidation behaviour of Ni‐Cr binary alloys with 10, 20 and 30 wt per cent Cr exposed in air for 50 h at 1,000°C. Analytical transmission electron microscopy along with light microscopy and X‐ray diffraction were used to characterise the oxide scale. It was observed that the scaling behaviour exhibited by the Ni‐Cr alloys changes from generally “non‐protective” to “protective” as their Cr content increases from 10 to 30 wt per cent. The Ni‐10Cr alloy formed a continuous network of NiO leading to scales of high thickness while Ni‐30Cr exhibited only α‐Cr₂O₃ at its surface. The Ni‐20Cr alloy exhibited all three oxide phases and an intermediate scaling behaviour.