Session Chair: Kevin, Qi Ge, Singapore University of Technology and Design Session Chair: Tun Seng Herng, National University of Singapore
10:30am - 11:00am Invited
Exploration of New Cemented Carbides by Selective Laser Melting Technique
National Tsing Hua University, Taiwan
Cemented carbide components such as drills, cutters, molds are important for the secondary processing industry, cemented carbides are usually very difficult to be fabricated into complex geometry by conventional liquid infiltration method. Additive manufacturing technique such as selective laser melting (SLM) presents a route to process this class of material into complex geometry. The present study has explored the possibility to use SLM process to fabricate cemented carbides. Detailed microstructure analysis has been conducted to compare those processed by the conventional mean with those by SLM. The traditional WC+Co system has shown severe balling phenomena during SLM and it can cause porous structure and rough surfaces. CALPHAD-based simulation has been employed to design new compositions more suitable for the SLM process. In summary, new compositions based on WC+high-entropy-alloy-binder have allowed denser microstructure and better mechanical property to be achieved by SLM.
11:00am - 11:15am Oral
Phase Transformation and Microstructure Characterizations of YAG:Ce Phosphor Ceramics Sintered by CO2 Laser
Yung-Tang NIEN, Yi-Chen CHEN
National Formosa University, Taiwan
Cerium-doped yttrium aluminum garnet (YAG:Ce) phosphors have been widely used in solid state lighting as a color convertor by changing the blue luminescence from a light emitting diode (LED) to yellow emission, which presents as warm or cold white light to naked eyes. YAG:Ce, either in powder or bulks forms, were conventionally fabricated by a solid state reaction (SSR) in a high temperature furnace, costing time to obtain high purity. In this presentation, we investigate the phase transformation mechanism and microstructure characterizations of YAG phosphor ceramics by CO2 laser sintering under various powers, offsets and focus distances. X-ray diffraction results indicated that all samples crystallized as a YAG phase without no obvious impurity phase in the power range of 15–40 W, e.g. YAP and YAM. Based on the laser spot size, there were no raw materials present in the laser sintered YAG:Ce as the offset was less than 0.5 mm. Regarding the surface roughness of YAG:Ce ceramics, a defocus set of laser beam was adopted to achieve much smooth surface than that by on-focus. The scanning speed of laser beam would also affect the surface morphology and microstructures in YAG:Ce. The reaction profile caused by laser ablation increased from 0.28 mm (15 W) to 2.68 mm (40 W), and it appeared deeper in the scanning sequence because of the low rigidity of YAG melts compared with solid precursors. Photoluminescence (PL) measurements revealed that the YAG:Ce sample by 15 W laser sintering upon blue light excitation presented more intense yellow emission (enhancement of 54%) as compared with YAG:Ce by SSR (1500 °C). The laser beams were believed to distribute activators (Ce) more homogeneously compared with SSR. Additionally, a rougher surface of YAG:Ce phosphor ceramics with periodic holes caused by laser ablation resulted in more excitation and emissivity of PL.
11:15am - 11:30am Oral
Processing Parameters to Fabricate High Density Tool Steel by Additive Manufacturing
Yong-Jin KIM, Sangsun YANG, Jaecheol YUN, Jungho CHOE
Korea Institute of Materials Science, South Korea
Tool steel of AISI H13 was fabricated by laser powder bed fusion(L-PBF) processing. The influence of the processing parameters on the density and microstructures of AISI H13 were investigated in this study. Typically, volumetric energy density (VED) was controlled by processing parameter in the PBF additive manufacturing. However, even if processing parameters have the same VED, densification behavior and microstructures were changed by the combination of laser power, scan speed, layer thickness, hatch space and the number of scanning. To control the VED with less processing parameters, we only changed the scan speeds from 100 mm/s to 1600 mm/s and the numbers of scanning from 1 to 8 times in the processing condition of the laser power at 90W, the layer thickness of 25 μm and the hatch space of 80 μm. Using the single laser scanning process, relative density of H13 tool steel was increased with the decrease of scan speed and converged to 96 % under 800 mm/s. To more increase the density, plural laser scanning process which consisted of first laser exposure and additional laser exposure was introduced. Scan speed of each laser exposure was controlled from 100 mm/s to 1000 mm/s. The surface of each layer was re-melted by additional laser exposure. Thus re-melting process reduced the residual pores that were generated by the keyhole mode melting in the first laser exposure. The highest relative density after plural laser scanning specimen was over 99 % with very fine microstructures.
11:30am - 11:45am Oral
Synthesis of Rare Sugars Containing Neoglycolipids by Enzyme Reaction
1Graduate School of Interdisciplinary New Science, Toyo University, Japan; 2Bio-Nano Electronics Research Centre, Toyo University, Japan
Rare sugars are monosaccharides and their derivatives naturally present in small amounts. These are known to have various effects on activities and functions of organisms and foods such as suppression of hyperglycemia, inhibition of cancer cell proliferation, dental treatment and the like. In this study, we aim to synthesis of rare sugars containing neoglycolipids for screening of rare sugar relating enzymes.
We synthesised neoglycolipids by mixing and heating sugars (glucose, ribose, allose, psicose and tagatose), pyridine, tert-butanol, octanoic acid and lipase (immobilised on macroporous acrylic resin) with a magnetic stirrer and an incubator. We purified the reactant by chloroform extraction and silica gel column chromatography.
Purified products were analysed using thin layer chromatography (TLC) and Fourier transform infrared spectroscopy (FT-IR). We confirmed new spot on TLC. FT-IR results showed peak of hydroxyl group and ester group. It have been indicated that neoglycolipids, consisting of rare sugars and octanoic acid, were synthesised.
We analysed cytotoxicity of neoglycolipids with human multiple myeloma cell (IM-9). We mixed cells and neoglycolipids. Then we incubated cells and neoglycolipids mixture in CO2 incubator. Cytotoxicity of neoglycolipids were calculated by measuring cell metabolism activities with alamar blue. It have been suggested that cytotoxic activity of the neoglycolipids increased with an increase in the concentration of them.
11:45am - 12:00pm Oral
Tuning the Phase Stability and Magnetic Properties in Laser Additively Processed Magnetic Alloys
1University of North Texas, United States; 2Nanyang Technological University, Singapore
While there have been a substantial amount of activities on additive manufacturing (AM) of structural alloys, there have been rather limited efforts on AM of functional alloys, such as magnetic materials. The present study will focus on preliminary investigations on laser additive processing of magnetic alloys using the laser engineered shaping (LENS) process from a feedstock consisting of a blend of elemental powders. Soft and semi-hard magnetic alloys of different types have been processed using LENS. These include those of the permalloy type, based on Fe-Ni, Ni-Fe-V and Ni-Fe-Mo compositions, as well as compositions based on Finemet, Fe73.5Si13.5B9Nb3Cu1. The primary focus will be on the widely used soft magnetic alloy, Fe-30at%Ni. Systematic changes in the laser-power and the travel speed have been correlated to the phase stability in the deposits, and the consequent magnetic properties. While columnar grains of the metastable fcc phase is the predominant phase for slower travel speeds, with increasing travel speeds, a substantial volume-fraction of a bcc, possibly martensitic, phase was observed. The bcc dominated microstructures exhibit a substantially higher saturation magnetization (Ms) as compared to the fcc dominated microstructures. This work shows the feasibility of AM processing of magnetic materials.