Improved High Temperature Oxidation Behaviour of AISI 347 Grade Stainless Steel by Superficial Coating of CeO₂

Abstract

Influence of superficially applied CeO₂ coating on the high temperature oxidation behaviour of AISI 347 grade stainless steel under different rates of heating followed by isothermal holding at 1273 K in dry air is reported. The reactive oxide coating not only reduced the oxidation rate but also facilitated imporved oxide scale adherence to the alloy substrate. The coated steel could withstand a number of thermal cyclings without scale rupture and exhibited further reduction in rate in sequential exposures. Reduced reaction rate has been attributed mainly to a change over in the rate controlling process from outward migration of cations to the ingress of oxidant species. Improved scale adhesion is due to change in chemical composition and grain size of the resultant oxide scale promoted by the formation of silicon-oxide stringers into the base alloy favouring pegging mechanism. Scale growth mechanism has been substantiated by post oxidation analyses using SEM, EDS, EPMA and XRD which could illustrate the role of reactive oxide coating and the formation of various cmplex oxide phases along with NiNb₂O₆.