The Effect of Surface Additives on the Oxidation of Chromia-Forming Alloys

Abstract

The influence of the surface application of active elements on the composition, morphology, adherence, and growth rate of oxide scales formed during high temperature exposure has been investigated. The active elements were applied as aqueous solutions of nitrate salts that were subsequently transformed into oxide. The active elements used were: Y, Ce, La, Hf, Ca, and Zr. The chromia-forming substrates used were AISI 304 and 310 stainless steels and IN 738, a nickel base alloy. To determine the effect of the minor alloying elements in stainless steels on the surface doping effect, Y was applied to three alloy modifications of AISI 304. The effect of the presence or absence of Mn and Si in the alloy on high temperature corrosion behavior was determined. Several different application techniques were used to determine which technique was most beneficial to the behavior of the oxide barrier scale.The application of Y, Ce, and La was found to enhance the oxidation resistance of the commercial stainless steels whereas no benefits were found for alloys with Hf, Ca, and Zr added to their surfaces. It was determined that Si had to be present in AISI 304 stainless steel for the enhancement of its oxidation resistance. There was no beneficial effect for modified 304 containing only Mn or neither Mn nor Si. The yttrium added and the untreated, modified AISI 304 with Si only showed more resistance to scale spallation than any other 304 alloy tested, modified or commercial. AbstractThe polarization behavior of various pure zinc, AI-Zn, and Zn-Ni coatings was studied to evaluate electrochemical methods for use in testing the performance of such coatings on sheet steel. Behavior in deaerated chloride solutions was found to simulate more nearly the good performance of pure zinc (galvanized) coatings in service. AI-Zn coatings exhibited low corrosion rates in both aerated and deaerated chioride solutions, yet they maintained active corrosion potentials and conferred galvanic cathodic protection to bare steel exposed in a scribe through the coating. The galvanic current, which provides cathodic protection for the steel in a scribe, was measured successfuly using the polarization resistance technique.( 1) Pyrex is a registered tradename of Coming Glass, Inc., Corning, New York.

330Cb alloy (Fe35Ni18Cr1Nb2Si) oxidation study between 800 and 1000 °C

“…Other authors pointed out that Mn 1.5 Cr 1.5 O 4 located at the external interface, could reduce the conversion of Cr 2 O 3 into a CrO 3 volatile oxide above 900 8C [29][30][31]. Some authors indicated that Mn 1.5 Cr 1.5 O 4 is nonprotective because it presents a porous structure [32,33]. Nevertheless, if manganese oxides crack at the external interface it does not affect the adherent protective chromia scale [34].…”

“…Then the silica phase leads to a decrease in the alloy oxidation rate [40]. The high oxygen affinity of silicon, permit its internal oxidation, developing SiO 2 precipitates at the internal interface [32,41]. Then, silica acts as a diffusion barrier and leads to peg the chromia scale on the substrate [42,43].…”

Surface modifications of AISI 420 stainless steel by low energy Yttrium ions

“…Small amounts (usually below 1%) of reactive elements (Sc, Ti, Y, Zr, Ce, La, ect.) clearly improve the oxidation behaviour of chromia-and alumina-forming alloys [6][7]. Several explanations are given about this effect, usually called reactive element effect (REE), namely a modification of the diffusion mechanisms, a reduction of vacancies condensation at the internal interface, a formation of reactive element oxide inclusions trapping alloy impurities [8][9][10].…”

High-temperature oxidation behaviour of EN-1.4301 stainless-steel after surface Ce deposition by a modified CVD method

“…An attractive way to overcome these problems while saving expensive and scarce metals like nickel is surface coating. From simple hot-dipping procedures 3 to sputtering, 4 chemical vapour deposition (CVD) 5 or ion implantation, 6 - number of processes described in the literature covers the whole set of known surface coating techniques, but most of them result either in inhomogeneous coatings or are costly enough to prevent their use in industrial applications.…”