3D printing of ceramic components by indirect selective laser sintering using a novel starting material based on polyamide-alumina granules

X. HUNG HUNG, Y.M.X; CAMERUCCI, M. A.; TALOU, M.H.

Darmstadt

Congreso; MSE 2022; 2022

Selective laser sintering (SLS) is a powder bed fusion process that uses energy provided by a laser to partially or fully melt the powders and then stack layer by layer to form an object from 3D model data. This additive manufacturing technique can be used to produce ceramic parts with complex geometries. However, the need of a fully enclosed high temperature heated chamber and a suitable high-energy laser beam has led to an alternative approach, namely indirect selective laser sintering (i-SLS), where ceramic parts are produced in a two-step process. The first step involves the employment of a binder system (e.g. polymers) to bond the ceramic particles together by laser melting in order to form a green part during the printing process. In the second step, the binder is removed from the green part (burn-out process) by slowly heating, and subsequently the green parts are sintered. In this work, the use of a novel granular powder bed system based on alumina (Al2O3), micron-sized graphite (laser energy absorbing material) and polyamide (PA612) for i-SLS 3D printing employing a low-power (2.3 W) blue (445 nm) diode laser was proposed in order to obtain porous alumina components. Composite granules were prepared via thermally induced phase separation (TIPS) process in dimethyl sulfoxide (DMSO). Volume fraction of  Polymer dissolved in DMSO and Al2O3/PA612 volume ratio were fixed in 0.05 and 40/60 vol.%, respectively. In order to determine the optimal amount of micron-sized graphite in the composite granules, different concentrations were studied (1 to 6.25 wt.% with respect to the Al2O3 total amount) using visible light absorption. The granules obtained were characterized by SEM, DSC, and Raman spectroscopy. The composite granules had a regular and slightly rounded shape and showed a thermal behavior similar to the as-received PA612. The effect of the laser beam scanning parameters, such as scan speed and scan spacing, and the layer height on the fabrication of green parts was evaluated. Porous alumina structures with both controlled geometry and porosity were successfully printed. Adequate bonding between layers was achieved, and no defects at the interface were detected. Finally, sintered components with good structural integrity that presented an apparent porosity of 61±2% and a microstructure characterized by the presence of equiaxed grains with an average grain size of 2,0±0,7 μm were obtained.