On the Oxidation Behaviour of Cold Sprayed CoNiCrAlY and NiCoFeCrAl Overlay Coatings

Compared to conventional metallic alloys, high entropy alloys (HEAs) offer new opportunities to design new-generation metallic materials with improved properties and performance. In particular HEA coatings may become alternatives to the traditional MCrAlY-type high temperature resistant metallic overlay coatings providing increased protection against oxidation, corrosion and wear, ultimately increasing the lifetime of a component over a wide range of operating conditions. Cold spray (CS) technique emerged as a robust alternative to thermal spray coating solutions delivering oxide-free and very dense MCrAlY coatings. We present a study on high-pressure cold spray deposition of a commercial NiCoFeCrAl HEA type feedstock using N2 as propelling gas and discuss the influence of feedstock properties and CS spray conditions on the deposited coatings over a large range of spray parameters. The microstructural and phase characteristics of the as-sprayed coatings were assessed via scanning electron microscopy (SEM) and energy dispersive X-Ray (EDX). Isothermal and cyclic high temperature exposures, at temperatures ranging between 900 to 1100°C were carried out to investigate coatings oxidation behaviour. Thermally grown oxide (TGO) layer and internal oxidation of NiCoFeCrAl HEA coatings were analyzed and will be discussed in comparison to the oxidation behaviour of CoNiCrAlY cold sprayed coatings tested in similar conditions.