Oxidation of Ni-Cr-Al Alloys Between 1000° and 1200°C

The oxidation of alloys in 0.1 atm of oxygen has been studied at temperatures of 1000°, 1100°, and 1200°C. Twenty‐one alloys with varying chromium 2–30 weight per cent (w/o) and aluminum (1–9 w/o) contents were examined. It was found that all of the alloys initially underwent a period of transient oxidation before steady‐state conditions were established. The transient period of oxidation usually did not exceed 1 hr and was characterized by rapid conversion of thin surface layers of the alloys to oxides with the subsequent formation of continuous layers of one of the following oxides: , , or . Steady‐state conditions were established with the formation of these continuous oxide layers, and oxidation occurred by three different mechanisms which were characterized by the growth of an external layer of over a subscale of and Al2O3, the growth of an external layer of over an subscale or the growth of a continuous, external layer of .