Effect of high-temperature preheating on the selective laser melting of yttria-stabilized zirconia ceramic

Selective laser melting (SLM) is one of the current rapid fabrication technology methods which has wide potential application in the aerospace, medical, consumer products and automotive industries. Currently, ceramic materials are not used as widely as metal and polymer materials due to the high melting point, high-temperature strength and low thermal conductivity, which influence the microstructure and density of ceramic samples during SLM fabrication. The most effective method of reducing cracks is the preheating at high temperature of the ceramic powder during SLM process. This paper presents the selective melting of yttria-stabilized zirconia (ZrO2-Y2O3 93-7) ceramic using a 1 μm wavelength fibre laser with high-temperature preheating at 1500-2500 °C, and an additional CHEVAL Nd-YAG laser for the preheating of the powder bed before scanning. In this paper, the influence of different laser powers and different scanning velocities on the microstructure, relative density and deformation of the ceramic sample is investigated; in particular, the effect of preheating on the morphology of the micro-cracks is discussed. Experimental results show that high-temperature preheating in 10 mm diameter range is possible with the Nd-YAG laser, and that orderly cracks are transformed into disordered little cracks by the high-temperature preheating. With preheating to 1500 °C, 2000 °C and 2500 °C, the relative density of the sample made by mixing fine powder (9-22.5 μm, 20 wt%) and coarse powder (22.5-45 μm, 80 wt%) is increased by 84% (without preheating) to 90-91%. The transformation of the monoclinic and cubic structures to a tetragonal structure is observed during the process of melting and cooling, and increasing the preheating temperature to 1500 °C, 2000 °C and 2500 °C is more suited to the formation of tetragonal crystals.