Development of Oxide Dispersion Strengthened Bondcoats by High-Velocity Air Fuel Spraying

The present study explores the employment of high-velocity air fuel (HVAF) technology to produce oxide dispersion strengthened (ODS) bondcoats for thermal barrier coating (TBC) applications. In earlier works, HVAF spraying has been demonstrated to produce high-performance bondcoats with enhanced TBC lifetime and reduced thermally grown oxide (TGO) growth, making it an interesting candidate to produce ODS bondcoats. Nine coatings were deposited utilizing two commercially available MCrAlY powders, NiCoCrAlYHfSi (Amdry 386) and NiCrAlMoTaYCSi (Metco 2253A), with different alumina powder additions. The alumina powder addition in the sprayed feedstock was performed via twin-feeding and mechanical blending approaches. All samples consisted of identical topcoats deposited by suspension plasma spraying (SPS). The microstructure and performance were assessed via scanning electron microscopy (SEM), isothermal oxidation, and thermal cycling fatigue (TCF) testing. The results show the successful incorporation of the alumina particles in the bondcoat, found to be preferentially embedded at splat boundaries. Strong positive correlations between the lifetime of the TBC and alumina content were observed. Higher concentrations of added alumina fostered the early growth of a dense and homogeneous alumina scale and hindered the growth of detrimental mixed oxides within the TGO layer, encouraging a more stable and protective scale formation. Although blended powder spraying resulted in a more homogeneous alumina distribution, the overall incorporation efficiency of added alumina remained limited. The oxide incorporation mechanisms in the bondcoats occurring during HVAF spraying have been discussed. The findings underscore the potential of HVAF for the fabrication of functional ODS bondcoats with enhanced durability.