The influence of reactive-element coatings on the high-temperature oxidation of pure-Cr and high-Cr-content alloys

A Further Study of the Beneficial Effects of Yttrium on Oxide Scale Properties and High-Temperature Wear of Stellite 21

“…It is known that yttrium may segregate at the oxide grain boundaries in the form of Y 2 O 3 or perovskite compounds such as YCrO 3 and inhibit outward diffusion of chromium ions; this helps to achieve the change from the outward diffusion of metallic elements to the inward diffusion of oxygen ions [24]. Krishnamurthy et al [25] suggest that the oxide film has relatively homogeneous compressive stress distributed within the oxide film, except in the regions near the oxide grain boundaries where the stress changes from compressive near the oxide/matrix interface to tensile near the oxide surface.…”

“…It is known that oxide scales could be improved by minor additions of rare-earth elements or reactive elements such as yttrium or hafnium [5][6][7][8]. Among these elements, yttrium and cerium perform most effectively [9]. There are several possible beneficial effects of yttrium on oxidation: (1) decreasing the oxide growth rate, particularly at temperatures close to 1,000°C [7,10], (2) improving the scale adherence to the substrate [11,12], (3) changing the oxidation mechanism from outward metal ions transport to inward oxygen ions transport [13,14], and (4) resulting in a finer grain microstructure of the oxide [15,16].…”

High Temperature Oxidation Behavior of Yttrium Dioxide Coated Fe-20Cr Alloy

“…In Y containing or Y 2 O 3 coated alloys, the Y ion in the oxide scale segregates to the grain boundaries and its radius (1.02 Å) being larger than the Cr and Fe ions (0.615 Å and 0.78 Å respectively) blocks the path of the diffusing alloy cations, decreasing thereby the oxidation rate of the alloy. 6,36 Hence, the influence of the Y 2 O 3 coating in reducing the oxidation rate of chromia forming alloys is twofold. It increases oxygen ion vacancies and thereby oxygen ion diffusion in the YCrO 3 compound.…”

High‐Temperature Oxidation

“…Conversely, the contribution made by short-circuit diffusion processes will be negligible at higher temperatures. Grain boundary diffusion in growing oxide scales has been reported for NiO [88,89], Cr 2 O 3 [90], Al 2 O 3 [91], and other product films.…”