The influence of silicon and yttrium on the scaling behaviour of an Austenitic Fe‐Cr‐Ni alloy under athermal conditions

Abstract

Abstract Data obtained using thermogravimetric and resonant frequency techniques and the results of structural analysis are used to evaluate the effects on oxidation of silicon and/or yttrium additions to an Fe‐24% Cr‐24% Ni alloy tested under thermal cycling conditions. Silicon promotes the formation of a protective chromia scale, but the accumulation of a mechanically weak, silicon‐rich oxide at the scale‐metal interface eventually leads to scale spalling. Yttrium alone is found to have little influence on the rate of alloy degradation, but in alloys containing silicon its presence prevents the accumulation of the interfacial silicon‐rich oxide layer. The temperature change required to cause scale failure and loss of protection to the substrate material is used as a measure of the mechanical integrity of the scales formed. The ability of alloys to form scales rapidly under conditions of frequent thermal cycling and to repair damage caused to a scale grown over a prolonged period of isothermal exposure are separately examined.