Abstract
This study deals with the isothermal oxidation behaviour of high velocity oxy-fuel sprayed MCrAlY coatings. Both free-standing coatings and coatings attached to IN738 and CMSX4 substrates underwent isothermal oxidation at 1100°C for up to 100 h. The effect of surface conditions (as sprayed and polished) has been investigated. Scanning electron microscopy and energy dispersive X-ray analysis were used to characterise the details of oxidation behaviour. The results have shown that both surface conditions and substrate type have a pronounced effect on oxidation behaviour. Extensive internal oxidation and nitridation was observed for polished coatings on Inconel 738 and can be attributed to the combined effects of titanium diffusion from the substrate and enhanced surface diffusion due to polishing.
Highlights
Thermal barrier coatings (TBCs)[1, 2] are used to protect turbine blades and similar components from the harsh conditions encountered in the hot gas stream
This paper studies the effect of substrate and surface condition on the oxidation behaviour of high velocity oxy-fuel sprayed CoNiCrAlY coatings
EDS analysis of the β and γ phases in the assprayed coatings after 100h oxidation showed the presence of titanium in the coating on Inconel 738: ~0.6 wt% was found in the γ phase and ~0.2wt% was found in the β phase
Summary
Thermal barrier coatings (TBCs)[1, 2] are used to protect turbine blades and similar components from the harsh conditions encountered in the hot gas stream. TBCs are layered structures, consisting of an outer, ceramic, layer which thermally insulates the underlying metallic component and a bond coat. As well as enhancing the adhesion of the ceramic top coat a key role of the bond coat is to provide corrosion and oxidation resistance. This is done by the generation of a protective thermally grown oxide (TGO), predominantly alumina, at the interface of the top coat and bond coat. A TGO forms rapidly but grows very slowly
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