Title

Precursor and processing conditions to make dense ceramic coatings using the solution precursor plasma spraying process

Date of Completion

January 2008

Keywords

Engineering, Materials Science

Degree

Ph.D.

Abstract

The objective of this research is to determine the precursor and processing conditions to produce nanograined ceramic coatings with high density and hardness using the Solution Precursor Plasma Spray (SPPS) process. These dense coatings would find potential applications as optical ceramics, wear resistant coatings and bioactive coatings. ^ Basic operating principles needed to create relatively dense coatings using the SPPS process have been discovered. These principles were then used to produce two new precursors and associated processing methods. It has been shown that dense coatings can be best produced if deposits arriving at the substrate are fully Incited. Multiple factors have been experimentally identified that provide dense coatings, including: (1) high solution concentration: (2) low melting temperature compositions; (3) large diameter gun nozzles: (4) high gun power and low liquid feed rates, (5) better entrainment of the droplets in the hot part of the plasma jet. ^ Based on these principles of dense coating formation, dense eutectic Al2O3-YSZ SPPS coatings were produced. The as-deposited coating has 95.6% density and hardness of 11.8 GPa. The thermal stability of as-sprayed dense eutectic Al2O3-7YSZ coatings was examined. High temperature heat treatments of the coating show that both the phase and nano-grain structure are very stable. The nanocomposite Al 2O3-7YSZ coatings are highly grain growth resistant due to the increased diffusion path of species along interphase boundaries. ^ The reproducibility of the principles to make dense ceramic coatings was successfully demonstrated by deposition of a low melting point TiO 2 coating that has desirable biological properties. A dense TiO 2 coating (96%) with a hardness of 7.6 GPa was achieved. ^ The conditions for making dense coatings have been identified. The discovery and demonstration of basic principles for making dense SPPS coatings is a fundamental advancement of the state of the art for SPPS coating technology. ^