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MCrAlY-Al 2 O 3 composite coatings were prepared by high-velocity oxygen fuel thermal spraying with bespoke composite powder feedstock for high-temperature applications. Powder processing via a suspension route was employed to achieve a fine dispersion of a-Al 2 O 3 submicron particles on the MCrAlY powder surface. This was, however, compromised by * 50% less flowability of the feedstock during spraying. Nevertheless, the novel powder manufacturing process introduced in this study has shown potential as an alternative route to prepare tailored composite powder feedstock for the production of metal matrix composites. In addition, the newly developed MCrAlY-Al 2 O 3 composite coatings exhibited superior oxidation resistance, compared to conventional MCrAlY coatings, with the formation of nearly exclusively Al 2 O 3 scale after isothermal oxidation at 900°C for 10 h. The addition of a-Al 2 O 3 particles in the MCrAlY coatings as a second phase was found to have promoted the formation of YAG oxides (Y x Al y O z) during spraying and also accelerated the outwards diffusion of Al, which resulted in enhanced oxidation resistance.

Ni50Cr thermally sprayed coatings are widely used for high temperature oxidation and corrosion in thermal power plants. In this study, a commercially available gas atomised Ni50Cr powder was sprayed onto a power plant alloy (ASME P92) using both gas and liquid fuelled high velocity oxy-fuel (HVOF) thermal spray. Microstructures of the two coatings were examined using SEM-EDX, XRD, oxygen content analysis and mercury intrusion porosimeter. The gas fuelled coating had higher levels of oxygen content and porosity.Shorter term air oxidation tests (4 h) of the free-standing deposits in a thermogravimetric analyser (TGA) and longer term air oxidation tests (100 h) of the coated substrates were performed at 700 ℃. The kinetics of oxidation and the oxidation products were characterized in detail in SEM / EDX and XRD. In both samples, oxides of various morphologies developed on top of the Ni50Cr coatings. Cr 2 O 3 was the main oxidation product on the surface of the coatings along with a small amount of NiO and NiCr 2 O 4 . Rietveld analysis was performed on the XRD data to quantify the phase composition of the oxides on both Ni50Cr coatings and their evolution with time.

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