Thin coatings of nitrate-convertecl oxides of Y, Zr, Hf, Ce, La, Ca, and A1 have been applied to the surface of a Fe-18 weight percent (w/o) Cr-5 w/o A1 alloy by hot-dipping. The influence of these coatings on the oxidation behavior of the alloy was studied at 1100 and 1200~ Results were also compared with the oxidation of a 1 w/o Hf-containing alloy of the same base composition, with or without the application of selected coatings. It was found that all of the coated FeCrA1 samples, apart from that coated with aluminum oxide, developed extremely convoluted A1203 scales. Oxide ridges several times larger than those formed on the untreated alloy developed at the oxidation temperature. These convoluted scales showed good spallation resistance after isothermal testing, but failed under thermal cyclic conditions. A thin layer of sulfur was found everywhere at the scale/alloy interface. The primary effect of the surface coatings was to increase the number of buckles in the oxide at the early stage of oxidation. Growth of the buckled oxide into large ridges took place by way of aluminum vapor phase transport and oxide lateral growth. The results are discussed in relation to the effect of reactive elements in improving scale adhesion., and it is suggested that the mechanisms governing this effect may be different for A1203-forming and for Cr203-forming alloys.The protection of high temperature alloys and coatings against oxidation is provided by the formation of slowgrowing oxide films, which often consist of A120~ and/or Cr203. One major limiting factor in the protection is extensive oxide loss from the surface, or oxide spaUing, under thermal cycling conditions. It has been known for over fifty years (1) that minor additions of oxygen active elements could significantly improve the spallation resistance of these oxide scales. Whittle and Stringer (2) reviewed the early literature on this effect, and noted that any element which has a higher affinity for oxygen than the scale-forming element, or fine dispersions of the reactive element oxide in the alloy, may be effective and suggested the name "reactive element effect" (REE). For A1203-forming alloys, it was pointed out (2, 3) that within experimental scatter, the addition of reactive elements does not alter the growth rate of alumina scales; the only consistently observed effect is the substantial reduction in scale spallation. For Cr203-forming alloys, the presence of reactive elements not only reduces the spallation, but also reduces the growth rate of the oxide film and modifies the growth direction of the scale from predominantly metal outward transport to predominantly oxygen inward transport.Numerous mechanisms have been proposed to explain the role of the reactive elements in reducing scale spallation (2). They can be separated into three groups: first, the scale/metal boundary is intrinsically weak, and the reactive element results in a strengthening; second, the scale/metal boundary is intrinsically strong, but is weakened by (for example) the segregation of...