Design and process optimization of a dual-fuel internal diameter HVOF system for CoNiCrAlY bond coats in aero-engine combustor liners

High-quality CoNiCrAlY bond coats are essential for the durability of thermal barrier coating (TBC) systems in aero-engine combustors, yet their deposition on small-diameter liners remains challenging. In this study, a dual-fuel internal diameter high-velocity oxy-fuel (HVOF) system was designed and optimized to overcome issues of limited accessibility and unstable powder delivery. Orthogonal experiments identified optimal spraying parameters, yielding bond coats with low porosity (∼1.2 %) and high adhesion strength (∼85 MPa). Microstructural analyses revealed dense coatings with uniformly distributed elements and localized O and Al enrichment, indicative of a thin thermally grown oxide (TGO). X-ray diffraction and transmission electron microscopy confirmed the γ-(Co, Ni, Cr) phase, with nanoscale grains and lattice strain contributing to peak broadening. Hardness values of 250–300 HV further demonstrated the coating's mechanical integrity. Engineering validation on an actual combustor liner confirmed uniform thickness (average 0.091 mm) and reliable deposition quality, establishing the developed system as a promising solution for producing durable bond coats in confined geometries.