Microstructure modulation strategy for the continuous uniform growth of quasi-columnar crystalline structure coatings based on high deposition rate powder

Plasma spray-physical vapor deposition (PS-PVD) allows the preparation of quasi-columnar coatings with columnar crystalline branching and dendritic structures, resulting in long life and high-thermal insulation properties. However, the microstructural feature of the coating is also responsible for the significant difference in hardness and elastic modulus in the coating's growth direction, which has an impact on its resistance to thermal shock and high-temperature erosion. This study summarizes the influence of motion parameters on the coating microstructure by adjusting the relative motion parameters between the spray gun and the sample, and proposes a deposition modulation strategy for a quasi-columnar structure coating that can be continuously and uniformly grown by increasing the powder feeding gradient. The increase of relative motion velocity reduces the growth interruption caused by the re-nucleation on the surface of columnar crystals, and the liquid phase and nanoclusters increase after the gas phase concentration is gradually increased to saturation with the increase of powder delivered. The gas-phase diffusion growth mode can be maintained continuously because the jet has sufficient energy to maintain the substrate temperature at low powder feed rates. The preparation of coatings with uniform columnar crystal microstructure and mechanical properties was realized, while the thermal cycle life of NiCrAlYSi/8YSZ thermal barrier coatings at 1100 °C was significantly improved, up to 1350 h–1650 h, and the high-temperature erosion rate was significantly reduced relative to the atmospheric plasma spraying (APS) coatings, which was improved to a certain extent.