Transparent spinel ceramics were additively manufactured by laser direct deposition, a blown powder additive manufacturing (AM) process. With a laser melt-growth process, the need for powder binders and post-processing procedures was eliminated. Transparent spinel ceramic samples were directly fabricated from micron-size magnesium aluminate spinel powders. The optical transparency of the printed spinel samples was mainly affected by residual porosity and cracking. Among other processing conditions, powder flow rate and laser power showed the most significant effects. An obvious transition from opaqueness to transparency was observed after reducing the powder flow rate down below 0.1 g/min. The optical transmittance, morphology, and phase composition of the printed spinel samples were systematically investigated. Microstructural aspects including porosity, cracking, and grain size were also characterized. A highest optical transmittance of 82% was obtained at a wavelength of 632.8 nm, which was nearly comparable to that of traditionally sintered counterparts. As laser power increased, residual porosity steadily decreased with a minimum porosity of 0.2% achieved. Meanwhile, total crack length obviously increased while a relatively smaller variation of average crack length was observed. The measured mechanical properties including hardness and fracture toughness were found to be nearly comparable to those of sintered counterparts. These well demonstrated the potentials of the proposed laser AM method in direct fabrication of transparent ceramics.
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