Splat formation and microstructure of solution precursor thermal sprayed Nb-doped titanium oxide coatings

TL;DR

This study investigates niobium-doped TiO2 coatings produced by solution precursor thermal spray, revealing how process parameters influence microstructure and phase composition, and proposing a model for the physico-chemical transformations involved.

Contribution

It provides new insights into the effects of flame temperature on coating porosity and phase content, and introduces a model for the transformation process during solution precursor thermal spraying.

Findings

Higher flame temperature reduces porosity.

Increased flame power increases anatase phase content.

Solution precursor spray allows controllable microstructure and phase composition.

Abstract

Solution precursor thermal spray can become a breakthrough technology for the deposition of coatings with novel chemistries; however, the understanding of the process that the feedstock material undergoes is still poorly understood when compared to more traditional presentations (i.e. powder and suspension). In this paper, niobium-doped TiO2 coatings were deposited by solution precursor high velocity oxy-fuel spraying, studying its microstructure and phase. It was reported that a lower flame temperature produced a highly porous coating, while the porosity was reduced at higher flame temperature. Investigation of the phase content showed that, contrary to our current understanding, a higher flame power implied an increase of the anatase phase content for solution precursor spray. Three methods were used: Rietveld refinement, peak height and peak area of the x-ray diffraction patterns. Additionally, single splats were analysed, showing that as the precursor travels through the flame, pyrolysis and sintering takes place to form the solid material. These results were used to derive a model of the physico-chemical transformation of the solution precursor. This work proves that solution precursor thermal spray is a promising technique for the deposition of doped ceramic coatings, being the microstructure and phase content controllable through the spraying parameters