A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 3 2 6 a combination of layer deposition (~100 µm thickness) by using ceramic slurries and a low melting SiO2 phase that further reacted with Al2O3 to fabricate products in the porosity range of 86% to 92%. The samples showed anisotropic (10% axial and 2% lateral shrinkage), and dense regions had an arithmetic average surface roughness, R a, of ~1.0 µm. Christian et al. [24] have fabricated 100% dense zirconia (ZrO2)/Al2O3 samples by preheating the ceramic to at least 1600°C. The authors used a laser with 60 W power, layer thickness of 50 µm, and a scanning velocity of 200 mm/s. Due to rapid melting, this process was hard to control and resulted in uneven crystal growth and coarse surface. Comparatively, laser engineered net shaping (LENS) is a laser beam deposition process where gas feed deposits powder, thus eliminating the need for a powder bed like SLS or SLM[25]. Application of ultrasonic vibrations during the LENS process has also ameliorated the cracking and inhomogeneity problem observed during laser processing of ceramics[26]. A CASE STUDY ON SLM OF MoAlB Experimental Details. SLM of MoAlB was explored as a case study to evaluate the applicability of SLM to a novel ceramic system never before printed using a laser-based AM approach. MoAlB is a ternary ceramic boride, which is a class of lightweight ceramics that possess exceptional thermal conductivity, thermal shock and corrosion resistance, and high toughness and hardness compared to traditional structural ceramics and metals, making it an attractive candidate for a myriad of applications ranging from aerospace to energy. A configurable additive testbed (CAT) was used. The term configurable implies that both the hardware and software can be modified to accommodate specific experimental designs. The CAT consists of an environmental chamber housing a laser powder bed fusion additive manufacturing build platform. The build environment was kept at < 10 ppm oxygen (O2), measured using a PureAire trace oxygen analyzer. The laser source was an IPG Model YLR-1000-WC-Y14, with a modulated continuous emission wavelength of 1070 nm and a maximum power of 1 kW. The scan system was a SCANLAB GmbH IntelliSCAN III 20 with a LINOS F-Theta-Ronar lens with a 255 mm focal length. The layer-wise powder depositions, in the SLM manner[27], were achieved by lowering the build platen by 50 µm, placing 20 grams of powder atop the build platen, then flattening and spreading the pile of powder using a 22-mm diameter titanium rolling spreader. The process of manufacturing MoAlB powders can be found elsewhere[28]. Description of Results. The results of a trial run to densify MoAlB particulates using SLM and corresponding energy dispersive spectroscopy (EDS) compositional data for points are shown in scanning electron microscopy (SEM) micrographs collected in backscatter electron (BSE) mode in Fig. 4, highlighting the variety of micro- structures and compositions attainable by the SLM process. Some issues that were observed included problems with spreadability and stability of MoAlB particles under laser. Currently, work on optimizing the processing parameters for designing 3D printed ternary metal boride structures is underway. CONCLUSIONS There are a variety of types of Fig.4 — SEMmicrographs of 3D printed MoAlB in (a) SE and (b) BSE at 100 W at 25 mm/s, (c) SE and (d) BSE at 200 W at 75 mm/s, (e) SE and (f) BSE at 400 W at 225 mm/s. The EDS compositional data for points D1 and D2, H1 and H2, and L1 and L2 labeled in (b), (d), and (f), respectively, are shown in tables located on the corresponding secondary electron images[28]. (b) (a) (c) (e) (d) (f)
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