Characterization of the Near-Eutectic Al₂O₃–40 wt% ZrO₂ Composite Coating Fabricated by Atmospheric Plasma Spray. Part II: Microstructure and Mechanical Properties of Nanocomposite Coating

Abstract

Near-eutectic Al₂O₃–40wt% ZrO₂ coating composed of nano-polycrystalline structure with grain size of 20–50 nm and amorphous phase was deposited by atmospheric plasma spray (APS) using nano-sized powders obtained by sol–gel technique as feedstock. The phase composition and microstructure of as-sprayed coating were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscopy (HRTEM). Meanwhile, some mechanical properties such as micro hardness and cohesion of as-sprayed coating were also studied. The results revealed that the as-sprayed coating consisting of α-Al₂O₃, γ-Al₂O₃, and metastable t-ZrO₂ was obtained with lower porosity about 7% and average microhardness of 726 kg/mm² with higher Weibull modulus 16 as compared to the recently reported coating with the same composition. Furthermore, the results from a comparative study in scratching test indicated the present coating exhibited a higher cohesion than that of pure Al₂O₃ coating and Al₂O₃–40 wt% ZrO₂ coating using spray-dried agglomerated powders as feedstock.

Keywords:

• Atmospheric plasma spray
• Coating
• Cohesion
• Near-eutectic
• Feedstock

ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China (No. 50772086, 50821140308), the High-Tech R&D Program of China (863, No. 2007AA03Z558), Research Fund for the Doctoral Program of Higher Education under contract No. 20060698008, National Basic Research Program (Grant No. 2007CB707702), and Research Fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province (AE201006).

Notes

normal force obtained from top surface scratching test.

normal force obtained from cross section scratching test.

Al₂O₃–40 wt% ZrO₂ coating *, using spray-dried agglomerated powders.

Al₂O₃–40 wt% ZrO₂ coating ⁺, present coating (using powders synthesized by sol–gel method).