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JTTEE5 18:536–545 DOI: 10.1007/s11666-009-9339-9 1059-9630/$19.00  ASM International

FeAl and NbAl3 Intermetallic-HVOF Coatings: Structure and Properties J.M. Guilemany, N. Cinca, S. Dosta, and I.G. Cano (Submitted September 9, 2008; in revised form March 25, 2009) Transition metal aluminides in their coating form are currently being explored in terms of resistance to oxidation and mechanical behavior. This interest in transition metal aluminides is mainly due to the fact that their high Al content makes them attractive for high-temperature applications. This is also a reason to study their resistance to wear; they may be suitable for use in applications that produce a lot of wear in aggressive environments, thus replacing established coating materials. In this study, the microstructure, microhardness, and wear and oxidation performance of FeAl and NbAl3 coatings produced by highvelocity oxy-fuel spraying are evaluated with two main aims: (i) to compare these two coating systems—a commonly studied aluminide (FeAl) and, NbAl3, an aluminide whose deposition by thermal spraying has not been attempted to date—and (ii) to analyze the relationship between their microstructure, composition and properties, and so clarify their wear and oxidation mechanisms. In the present study, the higher hardness of niobium aluminide coatings did not correlate with a higher wear resistance and, finally, although pesting phenomena (disintegration in oxidizing environments) were already known of in bulk niobium aluminides, here their behavior in the coating form is examined. It was shown that such accelerated oxidation was inevitable with respect to the better resistance of FeAl, but further improvements are foreseen by addition of alloying elements in that alloy.

Keywords

friction and wear, corrosion of HVOF coatings, high temperature oxidation, wear and corrosion

1. Introduction In recent decades, the challenge of using transition metal aluminides for structural applications has been approached in many different ways. These aluminides are called advanced materials due to their possible use in high-temperature applications with light-weight benefits and reasonably good strengths (Ref 1). Important advantages, such as high melting points, high strength-to-weight ratios and excellent resistance to hostile environments, mean that attention has been focused on nickel-, iron-, and titanium-based aluminides (Ref 2-4). The main shortcoming of these materials, however, is their poor ductility, which is improved either by changing the processing routes (Ref 5-8) or by the addition of ternary elements (Ref 2, 9-14). This lack of toughness is one of the reasons why they are good candidates for use as coatings. Moreover, regarding their high aluminum levels, it would not be possible to manufacture structural components with good load-carrying capabilities; therefore, they can be used as oxidation resistant coatings allowing the use of a substrate material with improved mechanical properties. J.M. Guilemany, N. Cinca, S. Dosta, and I.G. Cano, Cen