3D printing of nano-scale Al2O3-ZrO2 eutectic ceramic: Principle analysis and process optimization of pores

Abstract

Pores are common defects in the process of directed laser deposition (DLD) which not only greatly reduce the fracture toughness of ceramic materials, but also lead to the failure of shaped parts. In this paper, the formation mechanism of pores was analyzed and the effects of laser power, feeding rate, scanning speed and ultrasonic power on pores were investigated. Transmission electron microscope, scanning electron microscopy observation and X-ray diffraction analysis were carried out for sample microstructure and phase composition respectively. The relative density of samples was measured by the progressive focused ion beam and the porosity was calculated by image processing software Image. The results show that the pores are divided into gas holes and shrinkage cavities. The appearance of circular gas holes with smooth inner walls are caused by the feeding method by gas forced blowing, the gas mixed with powder itself, and the gas in the molten pool formed by gasification of low-melting impurities and alumina/zirconia during laser processing. The gas holes are evenly distributed in the cross-section of the thin-walled specimen parallel to the scanning speed. As the temperature changes drastically, the material around the melt solidifies first, the melt will be attached to the solidified material to shrink, so that the melt can not be filled as a solid and finally the shrinkage cavities are formed. Generally the shrinkage cavities are irregular and the pore wall is relatively rough, mainly concentrated on the top of thin-walled samples. The laser power has the greatest influence on the pores, which has the greatest effect on the porosity but little effect on the shrinkage cavities. After attaching the ultrasound, the gas holes are mainly distributed on the top of the sample, and the shrinkage cavities almost disappear due to acoustic streaming effect of ultrasonic. When the ultrasonic power is 180 W, the porosity reaches a minimum of 0.1±0.05% and the relative density is 99.9±0.1%.