Selective Oxide Deposition on Fe-Based Alloys in Dry High Temperature Environment – A Review

Abstract

This paper presents a review of an investigation on selective deposition of oxides on Fe-based alloys in dry high temperature environment. The oxidation reaction occurred in order to promote a protective oxide layer to prevent corrosion attack and secure the metal substrate from degrade further. As temperature increased, the oxidation rate was significantly increased. Selective oxidation of an alloy component significantly lowers the concentration of that particular metal element in the alloy subsurface zones. As the cyclic thermal conditions increases, associated mechanical damage to the oxide scale leads to the porous oxide growth and also accelerates the depletion of alloy element. Eventually, prolong the process a point is reached where diffusion of anion to the alloy becomes competitive with the outward diffusion of metal cation to the developed protective scale. Selective oxidation changes the mechanical properties mainly due to the grain boundary oxidation. It is considered a short-path circuit for diffusion and hence leads to weaken the cohesive strength of individual grains. The focus of this work is to review the complex oxidation process due to the occurrence of selective oxidation and oxide deposition with the growth of oxide scale at different rates and also due to the presence of defects and clear microstructure differences of Fe – based alloys. It is also to enhance basic knowledge regarding the oxide layer behaviour that requires an understanding of alloy composition and microstructure. The consequences of oxide growth are specifically relative to the effects of factors such as exposure duration, temperature and operating parameters that must be clearly understood.