The present study focuses on direct powder-bed selective laser processing (PBSLP) of two oxide ceramics; 8 mol% yttria-stabilized zirconia (8YSZ), and alumina-toughened zirconia (ATZ, 80wt.% 3YSZ + 20 wt.% alpha-alumina). During all the experiments, a commercially available selective laser melting/sintering (SLM/SLS) machine; Prox200 equipped with Nd:YAG laser (λ=1.065 μm) from 3D Systems is used. Both oxide ceramics (8YSZ and ATZ with d50 of 14 μm and 22 μm respectively) are provided from TOSOH and physically mixed with graphite powder (d50 of 19 μm) in a 3-axis powder shaker-mixer. With this addition, the laser absorption of both oxide powders at λ=1.065 μm has increased from <2% up to 65%. 
 
A combination of layering parameters; powder layer thickness (th) and compression rate (C%) are fixed for both powder blends (8YSZ+graphite and ATZ+graphite) at 100 μm of thickness and 300% compression. Once the layers are created, laser processing strategies and parameters (laser speed, laser power and hatch distance) are optimized for both oxides. The energy density needed to process 8YSZ and ATZ oxide ceramics is determined as 240 J/mm³ and 112 J/mm³ respectively. That is most likely due to lower melting temperature (TmATZ= ~2570 ^oC, Tm8YSZ = ~2700 ^oC) of ATZ and its higher thermal conductivity (κATZ = 2.9 W.m^-1.K^-1, κ8YSZ = 2.5 W.m^-1.K^-1). The relative density of 96.9% is measured for 8YSZ pieces, and 97.4% for ATZ. Then, a characterization path including dimensional accuracy measurements, cross-section imaging and porosity analysis, X-Ray diffraction, elemental mapping by EDX, and profilometer is followed to understand the effects of printing conditions on the microstructure of oxide ceramic parts. SEM imaging of cross-sectional cuts of ceramic parts revealed that cracking patterns and porosity distribution locally (zone close to the platform, core, and upper zone) change for both types of ceramics. Dimensional accuracy around 90% is obtained for ceramic pieces on the XY plane and around 96% for the Z direction. While 8YSZ shows mostly random cracking, ATZ shows a cracking pattern that is parallel to the fabrication direction. XRD analysis revealed that the cubic phase zirconia observed for 8YSZ powder remains the same after laser processing. On the other hand, the monoclinic + tetragonal phase zirconia structure of ATZ powder changes after laser processing, and only tetragonal phase zirconia can be observed in solid pieces. It is also observed that the relative intensity of the a-alumina phase in ATZ structure decreases from 10.31% to 1.32%, which indicates the transformation of the crystalline structure into an amorphous phase. The microstructure of the ATZ cross-section that consists of a dendritic-like matrix and three main phases can be observed. Elemental mapping of these three phases reveals that second phase is rich in aluminum and oxygen, while the third phase is rich in zirconium and oxygen. Also, it is observed that the first phase is a mixture of 2^nd and 3^rd phases in a smaller scale, most likely due to the very fast cooling rate of PBSLP.