Deposition of hydroxyapatite (HA) and yttria ceramic powders by low pressure cold spray involving vacuum atmosphere

This research explores the impact of environmental pressure conditions on the deposition efficiency and microstructural properties of ceramic coatings produced using Low-Pressure Cold Spray (LPCS) and Vacuum LPCS (V-LPCS) techniques. Hydroxyapatite (HA) and yttria ceramic powders were selected as the materials for investigation. The powders were characterized in terms of morphology, crystallinity, and specific surface area. Coatings were deposited via LPCS and V-LPCS, and their thicknesses were measured and compared for similar spray parameters only changing the surrounding pressure level, demonstrating significant differences attributable to powder characteristics and spraying parameters. Notably, V-LPCS produced coatings with greater thickness compared to LPCS, attributed to higher deposition rates. Single-track deposition experiments revealed enhanced deposition behaviour under vacuum conditions, including larger deposition areas and higher material adherence compared to LPCS. Yttria coatings also exhibited improved performance with V-LPCS, achieving increased thickness and denser microstructures relative to LPCS. Analysis of deposited splats revealed compaction and consolidation upon impact, with reduced fragmentation and greater deposition efficiency observed for V-LPCS. Specifically, HA splats demonstrated densification during impact, with a notable reduction in porosity from the initial powders to the resulting coatings. Overall, the findings highlight the superior deposition efficiency and coating quality achieved with V-LPCS, underscoring its potential to enhance cold spray processes for ceramic coating applications. • V-LPCS boosts deposition rates up to 5× compared to LPCS. • Coating properties are strongly influenced by feedstock morphology. • V-LPCS produces thicker coatings by minimizing bow-shock effects and modifying particle flow. • Optimizing flowability and spray settings can enhance results.