The effect of surface contamination on the transient oxidation of Ni-20Cr

When a metal surface is heated in an oxidising environment for the first ti me, an oxide scale is formed. This scale is not the product of a process th at occurs under steady state conditions, but is instead formed over a wide range of temperatures, as the sample heats. The oxides, often referred to a s transient scales, that are formed under these conditions are frequently v ery different from those found after long oxidation times. The research presented here considers the oxides formed during the heating of a commercial Ni-20%Cr alloy and examines the effect of surface contamina tion on the oxidation process. Also examined is the role of surface pretrea tment on the behaviour of the alloys during oxidation. The scales formed on these alloys are very thin (<100 nm) and the scales ha ve thus been examined using transmission electron microscopy (TEM) and scan ning transmission electron microscopy techniques (STEM). The samples produc ed were of cross-sections of the metal and oxide.