Microstructural and mechanical characterization of alumina scales thermally developed on iron aluminide alloys

Abstract

An understanding of the underlying phenomena when characterizing material performance requires knowledge in several areas, including the chemistry and physics of the early stages of oxidation, chemistry and bonding at the substrate/oxide interface, effect of segregants on the strength of bonding, transport processes through the scales that are formed during corrosion, mechanisms of residual stress generation and relief, and fracture behavior at the oxidekubstrate interface. Specific objectives of the program described here are to (a) systematically investigate the relationships among substrate composition and properties and scalekoating adherence, damage tolerance, and micromechanical properties; (b) use results from the investigation to prevent scaldcoating failure at elevated temperatures; and (c) identify conditions that lead to more damage-tolerant coatings and scales that are amenable to legitimate synthesis routes. The paper presents experimental data on microstructural characteristics of alumina scales that have been thermally developed on several Fe-based alumina-forming intermetallic alloys. In addition, adhesion data developed on the scales are presented, along with determinations of strain from data obtained by ruby fluorescence.

Corrosion performance of alumina scales in coal gasification environments

“…To examine the adhesion of thermally grown alumina scales to the substrate, Natesan et al 16 applied a tensile pull to separate the scale from the substrate. The technique they used involves attaching an epoxy-coated pin to the scale surface at a temperature sufficient to cure the epoxy.…”

Stress Determination in Thermally Grown Alumina Scales Using Ruby Luminescence

“…We have discovered that stresses can he determined in thermally grown alumina scales by measuring shifts in the "ruby fluorescence", a spectral doublet that occurs near 14000 cm-1 in chromium doped aluminas [3]. This fluorescence doublet results from a crystal field excitation in the Cr 3d electrons when Cr atoms are substituted for Al atoms in a-Al2O3.…”