An ultrasonic nanocrystal surface modification (UNSM) technique was applied to the thermally sprayed yttria-stabilized zirconia (YSZ) ceramic thermal barrier coating (TBC) deposited onto a hot tool steel substrate to improve the mechanical and tribological properties. The surface microstructure of the as-sprayed and UNSM-treated coatings was examined using a scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, while the hardness of the coatings was measured by Vicker`s hardness tester. The friction and wear behavior of the coatings was assessed using a ball-on-disk tribometer against bearing steel (SAE52100) ball at temperatures of 25 °C and 200 °C under dry reciprocating conditions. Results showed that the UNSM-treated coating had smoother surface, lower friction and higher resistance to wear compared to that of the as-sprayed coating. It was found that hybrid use of thermal spray coating (TSC) and UNSM technique is meaningful to bring together synergy effect of two emerging surface technologies.

This work investigates the reliability and reproducibility of scratch testing for YSZ and TiO 2 coatings deposited on NiCr bondcoats by plasma spraying. Scratch tests were conducted on cross-sections of the spray coatings. An image of the scratched area was taken after testing using an optical microscope in order to determine failure mode. With a statistical evaluation, the adhesion and cohesion strength were determined. The results show that cross-sectional scratch testing is effective for estimating the adhesion and cohesion strength of plasma spray coatings.

A typical feature of plasma sprayed zirconia-based coatings is that their depostion efficiencies are low. Thus, from the economic view of reducing cost, how to improve the depostion efficiency of plasma sprayed zirconia-based coatings is very important for practical application. In this paper, spray-dried nanostructured powders and conventional powders were used as feedstocks to deposit nanostructured and conventional zirconia coatings by atmospheric plasma spraying(APS). Deposition efficiencies for both nanostructured and conventional zirconia coatings deposited under different spraying parameters were comparatively measured. The obtained results revealed that the spray-dried nanostructured powders possessed higher deposition efficiency than that of conventional powders. In addition, it was found that spraying parameters had strongly influence on microstructure and microhardness of zirconia coatings. Therefore, in order to obtain high quality zirconia coating, proper spraying parameters must be considered.

Three kind of commercial ceramics powders, Al 2 O 3 , ZrO 2 and TiO 2 were deposited on 304 stainless steel plates by plasma spraying technique. Their porosities were evaluated with digital image analysis method. As the accuracy of this method depends significantly on metallographic preparation and metallography procedure for coating sample, we studied the effects of surface roughness, magnification and number of fields of view on the porosity. The proper values for the three parameters are discussed.