Preparation and characterization of nanocrystalline ZrO₂-7%Y₂O₃ powders for thermal barrier coatings by high-energy ball milling

Abstract

High-energy ball milling is an effective method to produce nanocrystalline oxides. In this study, a conventional ZrO₂-7%Y₂O₃ spray powder was ball-milled to produce nanocrystalline powders with high levels of crystalline disorders for deposition of thermal barrier coatings. The powder was milled both with 100Cr6 steel balls and with ZrO₂-3%Y₂O₃ ceramic balls as grinding media. The milling time was varied in order to investigate the effect of the milling time on the crystallite size. The powders were investigated in terms of their crystallite sizes and morphologies by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that under given milling conditions the powder was already nanostructured after 40 min milling. The crystallite size decreased significantly with increasing milling time within first 120 min. After that, a further increase of milling time did not lead to a significant reduction of the crystallite size. Ball-milling led to lattice microstrains. Milling with the steel balls resulted in finer nano-sized crystal grains, but caused the contamination of the powder. The nano-sized crystal grains coarsened during the heat-treatment at 1250°C.

Key words： nanostrucured powders; yttria stabilized zirconia (YSZ); high-energy ball milling; thermal barrier coatings

Acknowledgments

The authors would like to thank the German Science Foundation (DFG) for financially supporting the research work within the scope of DFG project ZH205/2-1.

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