Transverse microstructure of an oxide scale formed on a 20% Cr–25% Ni–niobium stabilized stainless steel

Abstract

A transverse section through a scale formed during the oxidation of 20% Cr–25% Ni–niobium stabilized stainless steel, in carbon dioxide, for 4900 h at 825 °C, has been examined by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These techniques have revealed the detailed microstructure and microchemistry of the three discrete silica, rhombohedral and spinel oxide layers comprising the scale. The variation of strain, degree of oxide order and crystallinity are consistent with the growth of the rhombohedral and spinel oxide being by outward cation movement. This is controlled by diffusion through the thin, amorphous silica layer after it has grown laterally between the rhombohedral oxide layer and the steel.

Stress effects in high temperature oxidation of metals

“…24, Route II, can be deduced by direct application of elasticity theory'r'" as (76) which is the solution for a clamped plate of thickness overlying a circular area of decohesion of radius R. If, as is being assumed, the only source of compressive stress is that deriving from differential thermal contraction, the critical temperature drop~7b to initiate buckling is interface. Note, however, that in some circumstances a curved substrate can develop tensile stress across the interface and, thus, possibly aid the process of decohesion (see the section 'Curved oxide/metal interface' above).…”