Critical pressure threshold governing microstructure and properties of low-power PS-PVD thermal barrier coatings

Pressure significantly affects the microstructure and performance of coatings fabricated by plasma spray–physical vapor deposition (PS-PVD); yet its specific role remains insufficiently understood. In this work, a novel low-power PS-PVD system, defined by a torch power below 40 kW, was developed to investigate pressure effects. Lower pressures generally favor vapor-phase deposition. However, in this study, a critical pressure of 300 Pa was identified, governing the microstructural evolution of yttria-stabilized zirconia (YSZ) thermal barrier coatings, with vapor-phase deposition inhibited at lower pressure and liquid-related features enhanced at higher pressure. Combined experiments and CFD simulations provide insight into this non-monotonic pressure dependence. At 400 Pa, hybrid vapor–liquid coatings form, retaining comparable thermal conductivity to vapor-dominated coatings at 300 Pa but exhibiting enhanced hardness and wear resistance, offering a favorable trade-off between structural compliance and thermo-mechanical durability. The low-power strategy mitigates electrode erosion and enables coating of thermally sensitive components.