Abstract
MCrAlY–Al2O3 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 α-Al2O3 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–Al2O3 composite coatings exhibited superior oxidation resistance, compared to conventional MCrAlY coatings, with the formation of nearly exclusively Al2O3 scale after isothermal oxidation at 900 °C for 10 h. The addition of α-Al2O3 particles in the MCrAlY coatings as a second phase was found to have promoted the formation of YAG oxides (YxAlyOz) during spraying and also accelerated the outwards diffusion of Al, which resulted in enhanced oxidation resistance.
Highlights
Alumina-forming coatings, known as bond coats, have been widely used on hot section of gas turbine engines since early 1960s (Ref [1,2,3,4,5])
MCrAlY–Al2O3 composite coatings were prepared by high-velocity oxygen fuel thermal spraying with bespoke composite powder feedstock for high-temperature applications
MCrAlY feedstock, the composite feedstock exhibits a good dispersion of alumina submicron particles mainly attached on the surface of the MCrAlY surface with a radius ratio in the range of 40 * 80:1
Summary
Alumina-forming coatings, known as bond coats, have been widely used on hot section of gas turbine engines since early 1960s (Ref [1,2,3,4,5]). A bond coat system of MCrAlY (M = Ni/Co) alloy has been developed based on a balance among several aspects that include oxidation, corrosion and ductility (Ref [6,7,8]). High-velocity oxygen fuel (HVOF) thermal spraying is one of the most widely used coating techniques for the deposition of MCrAlY coatings for high-temperature corrosion/oxidation protection (Ref [9,10,11]). HVOF thermal-sprayed MCrAlY coatings are normally used within the temperature range of 950-1100 °C with the formation of a 1-10-lm-thick protective a-Al2O3 scale. Metastable h- and c-Al2O3 that are non-protective (voids) would form instead in the temperature range of 700-950 °C (Ref 15), which are fast growing with oxidation rate constants (kp) being [2,3] orders of magnitude higher than that of a-Al2O3
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