Effect of spraying parameters on the crystallinity and microstructure of solution precursor plasma sprayed coatings

Abstract

Solution precursor plasma spraying (SPPS) is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs). The zirconium nitrate (Zr(NO3)4·5H2O) and the ytterbium nitrate solution were used as precursor solution to prepare Yb2O3 stabilized ZrO2 (YbSZ) coatings by SPPS. The spraying distance and plasma power were varied to study the effect on the coating crystallinity and microstructure. The SEM images showed that YbSZ coatings had nanoparticles, agglomerations and pores. With the increase of the spraying distance and plasma power, a skeletal structure can be observed, and the particles were connected through the skeletal structure. The porosity of coatings was analyzed by image processing system. The average porosity of the YbSZ coatings increased from 34.6% to 39.9% with the spraying distance from 60 mm to 100 mm. And it decreased from 40.2% to 27.6% with the spraying power from 30 kW to 42 kW. The crystallinity was calculated according to the XRD patterns and the full width at half maximum (FWHM) of Raman peak. The results showed that the crystallinity was decreased from 75.2% to 23.8% while the FWHM varied from 32.1 to 37.9 cm−1 when the spraying distance increased from 60 mm to 100 mm. And the crystallinity was increased from 12.7% to 35.6% while the FWHM varied from 40 to 32.9 cm−1 when the plasma power increased from 30 kW to 42 kW. It appeared m-ZrO2 when the spraying distance was 60 mm.