Air Plasma-Sprayed MCrAlY Coatings with Low Oxide Content Enabled by Adding a Deoxidizer

MCrAlY coatings prepared by plasma spraying have been commonly utilized as a thermal protective coating for crucial heated end components due to their high mechanical properties and excellent high-temperature oxidation resistance in aggressive environments. However, the oxides introduced during the preparation process have an adverse impact on the properties of the MCrAlY coatings. In the present work, an attempt was made to deposit NiCrAlY coatings by air plasma spraying (APS) with a low oxide content achieved by introducing carbon as a deoxidizing element. During spraying, the carbon is preferentially oxidized and the formed gaseous CO is completely removed rapidly. Thus, the in-flight oxidation of metal elements can be suppressed to achieve oxide-free particles. Individual in-flight droplets were collected with liquid N₂ to clarify the deoxidation effect. Results demonstrate that the oxygen-free NiCrAlYC droplets can be achieved by adding deoxidizing element carbon. The oxide content of NiCrAlYC particles is 0.43 wt.%, being much lower than the 2.87 wt.% of conventional NiCrAlY particles. The adhesive strength test yielded an adhesive strength higher than 71 MPa for NiCrAlY coatings APS-prayed by the oxide-free NiCrAlYC molten droplets, which is much higher than 53 MPa for the conventional NiCrAlY coatings.