Sliding Wear Behavior of Plasma Sprayed Zirconia Coating on Cast Aluminum against Silicon Carbide Ceramic

The sliding wear behaviors of ZrO2-22 wt pct MgO （MZ） and ZrO2-8 wt pct Y2O3（YZ） coatings deposited on a cast aluminum alloy with bond layer （NiCrCoAlY） by plasma spray were investigated under dry test conditions at room temperature. Under all load conditions, the wear mechanisms of the MZ and YZ coatings were almost the same. The material transfer and pullout were involved in the wear process of the studied coatings under the test conditions. The wear rate of the MZ coating was less than that of the YZ coating. While increasing the normal load, the wear rates of the MZ and YZ coatings increased. SEM was used to examine the worn surfaces and to elucidate likely wear mechanisms. Energy dispersive X-ray spectroscopy （EDX） analysis of the worn surfaces indicated that material transfer occurred in the direction from the SiC ball to the disk. Fracture toughness had a significant influence on the wear performance of the coatings. It was suggested that the material transfer played an important role in the wear behavior.

Sinterability of Zirconia Top Coat of Investment Mold for Ti Alloy

In this paper. zirconia is used as top mold material for Ti investment casting. Top mold samples are made by proper mold building technology. The effect of different sintering temperature on chemical composition, microstructure and residual bending strength of the top mold sample is Studied. The volume and homogeneity of the air holes in the top mold are determined by sintering temperature. and finally determined the residual bending strength of the mold sample was determined.

Characteristics of helium DC plasma jets at atmospheric pressure with multiple cathodes

A novel DC plasma torch with multiple cathodes is developed for generating laminar, transitional and turbulent plasma jets. The jet＇s characteristics, including jet appearance, voltage fluctuation, thermal efficiency, specific enthalpy, and distributions of temperature, pressure, and velocity, are experimentally investigated. The results show that as the gas flow rate increases, the plasma jet transforms first from the laminar state to the transitional state and second to the turbulent state. Compared with the transitional/turbulent jet, the laminar jet possesses not only a better stability and a longer hightemperature zone but also a higher average/core temperature and a higher specific enthalpy at the nozzle＇s outlet. With the change of jet states from the laminar to the turbulent flow, the core pressure and velocity at the nozzle＇s outlet increase,while the decaying rates of temperature/pressure/velocity along the jet＇s axial direction increase sharply. Furthermore, applications of laminar, transitional and turbulent jets for zirconia spray coating are described. The test results indicate that the long laminar jet is favorable for the deposition of a high-quality coating because the powder particles injected into the laminar jet may have better heating and lower kinetic energy.

In-flight particle characterization and coating formation under low pressure plasma spray condition

Yttria-stabilized zirconia（ YSZ） coatings were deposited by low pressure plasma spray（ LPPS） in 1.0× 10^4 Pa,1.5 × 10^4 Pa,and 2.5 × 10^4 Pa. Both in-flight particle diagnostic detected by DPV-2000 system and ANSYS-FLUENT software were used to study the connection between the parameters of flying particles and the coating formation,which might help to recognize the relationship between the operation parameters and the coatings quality. The results of simulation showed that particles in a lower spray pressure could achieve a higher velocity. The particle velocity was around 380 m/s at a distance of 35 cm from the nozzle at 1.0 × 10^4 Pa while only 300 m/s at 2.5 × 10^4 Pa in actual measurement.The results showed that the velocity of particles increased with decreasing the spray pressure,which might enhance the flattening rate of coatings and thereby decreased the porosity. The deposited YSZ coating with the lowest porosity can be gained under 1.0 × 10^4 Pa condition.