The oxidation of alloys

Abstract

A review of the principles governing alloy oxidation is presented together with the means by which practical oxidation-resistant alloys have been developed. The reactions involved are complex and involve acquiring data from many fields. Wagner developed the basic diffusional models for the formation of oxide scales, but these need to be expanded using detailed physical and metallurgical studies of the alloy phases, oxides and their defects, as well as the mode of scale formation and the structural relationships between alloy and oxide scale.At this time the engineering solutions have outstripped fundamental understanding, but an attempt is made to show how the development of oxidation theory has contributed to this effort by a term now referred to as 'informed empiricism'.There is no doubt that further fundamental studies will help improve present alloys in the continuing requirements of new atmospheres and higher temperatures.

Isothermal Oxidation Comparison of Three Ni-Based Superalloys

“…In agreement with this, Wallwork's [87], work on the effect of oxidation with different chromium contents (8, 13.5 and 22 at. %) revealed an alloy with lower chromium content had an outer NiO scale and spinel in the subsurface region.…”

The Oxidation Behaviour of Alloys Based on the Ni–Co–Al–Ti–Cr System

“…In addition, alloys 101a (Ni-60Co-2.5Al-7.5Ti-10Cr) and 103c (Ni-20Co-7.5Al-2.5Ti-10Cr) showed large amplitude rippling of the oxide scale. This phenomenon is related to the formation of the Cr depleted layer and is known to occur when diffusion through the chromium oxide is faster than the supply of Cr from the base alloy [13]. In such circumstances, a region with a steep chromium concentration gradient will develop and any perturbations in the oxide-metal interface will be unstable and grow into the alloy.…”

“…The oxidation behaviours of simple binary and ternary Ni-and Co-based alloys, as well as those of more complex, commercially available superalloys, are well established [6][7][8][9][10][11][12][13][14]. Previous studies on Ni-Cr and Co-Cr binary alloys have determined that a concentration of Cr in excess of 10 wt.% is required to allow the formation of a protective chromia layer [6].…”

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

“…Variation of the parabolic rate constant 60 80 k, with alloy composition for Ni-Cr alloys at 1000 "C in oxygen at 1 atm. From reference [9]. 20 …”