Tailoring the crystallographic texture of biomedical metastable β-type Ti-alloy produced via laser powder bed fusion using temperature-field simulations

Recently, the use of laser powder bed fusion (LPBF) to create crystallographic textures, such as single-crystal-like and polycrystalline textures, has attracted attention. However, the relationship between the LPBF conditions and the resulting texture is unclear. This study investigates the effects of the LPBF conditions (laser power and scanning speed) on the texture by estimating the solidification behavior using temperature-field simulations. Herein, we show for the first time that laser power and scanning speed negatively and positively affect the solidification rate R, respectively, and do not affect the thermal gradient G significantly. Thus, when the laser power decreases and scanning speed increases, the G/R ratio decreases and polycrystal formation is enhanced. This is consistent with practical observations.Ishimoto T., Suganuma R., Nakano T.. Tailoring the crystallographic texture of biomedical metastable β-type Ti-alloy produced via laser powder bed fusion using temperature-field simulations. Materials Letters 349, 134835 (2023); https://doi.org/10.1016/j.matlet.2023.134835

Surface residual stress and phase stability in unstable β-type Ti–15Mo–5Zr–3Al alloy manufactured by laser and electron beam powder bed fusion technologies

The differences between the physicochemical properties of the laser and electron beam powder bed fusion (L- and EB-PBF) methods are yet to be explored further. In particular, the differences in the residual stress and phase stability of alloys with unstable phases remain unexplored. The present work is the first to systematically investigate how the heat source type and process parameters affect the surface residual stress and phase stability of an unstable β-type titanium alloy, Ti–15Mo–5Zr–3Al. The surface residual stress and β-phase behavior were studied using high-precision X-ray diffraction (HP-XRD). Significant differences were observed between the two methods. The L-PBF-made specimens exhibited tensile residual stresses of up to 400 MPa in the surface area. HP-XRD analysis revealed a stress-induced lattice distortion, interpreted as a transitional state between the β-phase and α”-phase. In contrast, the EB-PBF-made specimens showed no significant residual stress and had an undistorted β-phase coexisting with the hexagonal α-phase caused by elemental partitioning. This study provides new insights into the previously neglected effects of L-PBF and EB-PBF in unstable β-type titanium alloys.Takase A., Ishimoto T., Suganuma R., et al. Surface residual stress and phase stability in unstable β-type Ti–15Mo–5Zr–3Al alloy manufactured by laser and electron beam powder bed fusion technologies. Additive Manufacturing, 47, 102257. https://doi.org/10.1016/j.addma.2021.102257

Lattice distortion in selective laser melting (SLM)-manufactured unstable β-type Ti-15Mo-5Zr-3Al alloy analyzed by high-precision X-ray diffractometry

A peculiar lattice distortion in a selective laser melting (SLM)-manufactured unstable β-type Ti-15Mo-5Zr-3Al was observed for the first time, through high-precision X-ray diffraction (XRD) analyses. After SLM, Ti-15Mo-5Zr-3Al exhibited a body-centered-tetragonal structure instead of a body-centered-cubic structure; the c-axis was 0.63% shorter than the a-axis. The XRD analyses also revealed tensile residual stresses of 210 ± 12 MPa at the specimen surface. A numerical simulation indicated rapid cooling during the SLM, which could have caused the residual stresses. A comparison of the partially stress-released SLM specimen and an electron beam melting-manufactured specimen with negligible residual stress suggested that the residual stress caused by the rapid cooling in SLM induced the lattice distortion. This finding is not consistent with the previous understanding that residual stress changes the lattice parameter without lattice distortion. This study provides new insight into lattice distortion generated by a combination of SLM-specific ultrarapid cooling and unstable phases.Takase A., Ishimoto T., Suganuma R., et al. Lattice distortion in selective laser melting (SLM)-manufactured unstable β-type Ti-15Mo-5Zr-3Al alloy analyzed by high-precision X-ray diffractometry. Scripta Materialia, 201, 113953. https://doi.org/10.1016/j.scriptamat.2021.113953

Keggin-type molybdovanadophosphoric acids loaded on ZSM-5 zeolite as a bifunctional catalyst for oxidehydration of glycerol

Glycerol is a promising renewable feedstock for the manufacture of C3 derivatives. We investigated the one-pass oxidehydrarion of glycerol through the dehydration of glycerol into acrolein, followed by the oxidation of acrolein. A novel bifunctional catalyst for this reaction was prepared by loading the Keggin-type molybdovanadophosphoric acid H3+xPVxMo12-xO40 (x = 0–3) on ZSM-5 (MFI) zeolite (Si/Al = 45) exhibiting both dehydration and oxidation activity. H5PV2Mo10O40 and H6PV3Mo9O40 were stable and dispersed on ZSM-5 zeolite, and the acidic property of the ZSM-5 zeolite was retained. The oxidehydration of glycerol was catalyzed by H5PV2Mo10O40 loaded on the ZSM-5 zeolite with high selectivity of acrylic acid. In-situ IR analysis suggests that acrolein molecules adsorbed on H5PV2Mo10O40/ZSM-5 were converted into acrylic acid due to the inhibition of side-reactions such as polymerization and auto-condensation, which induced coke formation, compared with the other Mo and V-based oxides loaded on ZSM-5 zeolite

Obstacle Detection Based on Occupancy Grid Maps Using Stereovision System

金沢大学理工研究域機械工学系We previously reported on an obstacle detection method using a stereovision system. The system generated disparity images that include three-dimensional spatial information. Using these images, obstacles could be detected, but some false positives were generated. In this paper, we attempt to eliminate this problem and propose a method that generates Occupancy Grid Maps based on measurements from a stereovision system which leads to robust obstacle detection. Furthermore, it is confirmed that high distance accuracy can be achieved by using our method. © 2010 Springer Science+Business Media, LLC

A simple biofuel cell cathode with human red blood cells as electrocatalysts for oxygen reduction reaction

A red blood cell (RBC) from human exhibited direct electron transfer (DET) activity on a bare indium tin oxide (ITO) electrode. A formal potential of 0.152 V vs. a silver-silver chloride saturated potassium chloride (AglAgClIKCI(satd.)) was estimated for the human RBC (type AB) from a pair of redox peaks at around 0.089 and 0.215 V (vs. AglAgClIKC1(satd.)) on cyclic voltammetric (CV) measurements in a phosphate buffered saline (PBS; 39 mM; pH 7.4) solution. The results agreed well with those of a redox couple for iron-bearing heme groups in hemoglobin molecules (HbFe(1I)/HbFe(III)) on the bare ITO electrodes, indicated that DET active species were hemoglobin (Hb) molecules encapsulated by a phospholipid bilayer membrane of the human BBC. The quantity of electrochemically active Hb in the human RBC was estimated to be 30 pmol cm(-2). In addition, the human RBC exhibited oxygen reduction reaction (ORR) activity in the dioxygen (O2) saturated PBS solution at the negative potential from ca. 0.15 V (vs. AglAgClIKC1(satd.)). A single cell test proved that a biofuel cell (BFC) with an O2IRBCIITO cathode showed the open-circuit voltage (OCV) of ca. 0.43 V and the maximum power density of ca. 0.6811W cm(-2).ArticleBIOSENSORS & BIOELECTRONICS. 55:14-18 (2014)journal articl

Comparison of microstructure, crystallographic texture, and mechanical properties in Ti–15Mo–5Zr–3Al alloys fabricated via electron and laser beam powder bed fusion technologies

Depending on the application, establishing a strategy for selecting the type of powder bed fusion technology—from electron beam (EB-PBF) or laser powder bed fusion (L-PBF)—is important. In this study, we focused on the β-type Ti–15Mo–5Zr–3Al alloy (expected for hard-tissue implant applications) as a model material, and we examined the variations in the microstructure, crystallographic texture, and resultant mechanical properties of specimens fabricated by L-PBF and EB-PBF. Because the melting mode transforms from the conduction mode to the keyhole mode with an increase in the energy density in L-PBF, the relative density of the L-PBF-built specimen decreases at higher energy densities, unlike that of the EB-PBF-built specimen. Although both EB-PBF and L-PBF can obtain cubic crystallographic textures via bidirectional scanning with a 90° rotation in each layer, the formation mechanisms of the textures were found to be different. The texture in the build direction is mainly derived from the vertically grown columnar cells in EB-PBF, whereas it is derived from the vertically and horizontally grown columnar cells in L-PBF. Consequently, different textures were developed via bidirectional scanning without rotation in each layer: the and aligned textures along the build direction in L-PBF and EB-PBF, respectively. The L-PBF-built specimen exhibited considerably better ductility, but slightly lower strength than the EB-PBF-built specimen, under the conditions of the same crystallographic texture and relative density. We attributed this to the variation in the microstructures of the specimens; the formation of the α-phase was completely absent in the L-PBF-built specimen. The results demonstrate the importance of properly selecting the two technologies according to the material and its application.Sun S.H., Hagihara K., Ishimoto T., et al. Comparison of microstructure, crystallographic texture, and mechanical properties in Ti–15Mo–5Zr–3Al alloys fabricated via electron and laser beam powder bed fusion technologies. Additive Manufacturing, 47, 102329. https://doi.org/10.1016/j.addma.2021.102329

Effect of scan length on densification and crystallographic texture formation of pure chromium fabricated by laser powder bed fusion

Processing of pure chromium (Cr) encounters substantial challenges due to its high melting point and intrinsic brittleness. Although laser powder bed fusion processing (LPBF) offers a novel processing approach by reaching the temperature required to melt pure Cr, the high ductile-to-brittle transformation temperature (DBTT) of pure Cr prevents the density of the as-built Cr component from reaching the level of industrial acceptance. This study focuses on raising the quality of the as-built pure Cr components to the industrial level while considering the effect of scan length on densification and crystallographic texture. It was found that short scan length induced by feature size improved the density of as-built specimens while strengthening the texture suggesting uniform heat distribution and lower thermal gradients as a result of short time intervals in scanning tracks and layers. It was discovered that cracking caused by residual stress was detrimental to densification due to the DBTT characteristic of pure Cr, which was localized at high-angle grain boundaries (HAGBs) with high misorientation. The decrease in density and misorientation of HAGBs owing to the increase in grain size and texture strength, respectively, improved the density of as-built Cr up to 97.6% and altered its mechanical properties. Therefore, these findings offer new insight into the LPBF processing of metals with high DBTT characteristics.Gokcekaya O., Ishimoto T., Todo T., et al. Effect of scan length on densification and crystallographic texture formation of pure chromium fabricated by laser powder bed fusion. Crystals, 11, 1, 1. https://doi.org/10.3390/cryst11010009

Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas

In metal additive manufacturing, the microstructures and associated mechanical properties of metal specimens can be controlled over a wide range. Although process parameters are considered important in the fabrication of functional parts, the effect of atmospheric gas has not been comprehensively documented. In laser powder bed fusion (LPBF), gas flow is used to eliminate fumes generated by laser irradiation. Simultaneously, the gas removes heat from the laser-irradiated part, which is exposed to high temperature. In this study, we investigated the capacity of helium as an alternative to argon, which is conventionally used as the LPBF atmosphere gas. He has a higher thermal conductivity and lower gas density than Ar, which may result in enhanced heat removal from the Ti-6Al-4V alloy during fabrication. Numerical simulations suggest a greater cooling rate under He flow. Further, the material built under He flow contained finer α' martensite grains and showed improved mechanical properties compared to those fabricated under Ar flow, despite the identical laser irradiation conditions. Thus, He gas is advantageous in LPBF for fabricating products with superior mechanical performance through microstructural refinement, and this is a result of its capacity for cooling and fume generation inhibition. Therefore, this study reveals the importance of the choice of atmospheric gas because of its effects on the characteristics of metallic specimens fabricated using LPBF.Amano H., Ishimoto T., Suganuma R., et al. Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas. Additive Manufacturing, 48, 102444. https://doi.org/10.1016/j.addma.2021.102444

Shape selectivity in toluene disproportionation into para-xylene generated by chemical vapor deposition of tetramethoxysilane on MFI zeolite catalyst

Dependence of shape selectivity for para-xylene production by toluene disproportionation on conditions of chemical vapor deposition (CVD) of tetramethoxysilane on MFI (ZSM-5) zeolite were investigated in detail. The CVD after pelletization was necessary to obtain 0.7–1 mm particles with high selectivity. The influences of preparation conditions on the selectivity were investigated in detail to find the optimum conditions. The parent zeolite with small number of Brønsted acid sites on the external surface brought the high selectivity after the CVD. The catalyst prepared in the optimized conditions showed the selectivity 99.7% at ca. 10% of the toluene conversion