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An interfacial microstructural study was carried out to clarify the hardening mechanism of an as-built Co–Cr alloy fabricated by selective laser melting (SLM). Using transmission electron microscopy, we found a unique martensitic lamellar microstructure with a specific orientation relationship between the α-Co and e-Co phases; specifically, a nanoscale microstructure consisting of (111)α-Co//(000 2 ¯ )e-Co and [0 1 ¯ 1]α-Co//[ 1 ¯ 2 1 ¯ 0]e-Co was formed on the Co–Cr alloy. The Co–Cr alloy fabricated by SLM with a martensitic microstructure achieved a Vickers hardness value of approximately 369.36 ± 11.86 HV without any secondary-phase particles such as carbides.

A facile and efficient synthesis of tetrahydro-β-carbolines (tryptolines) in one step from tryptamine and aldehydes, in an environmentally friendly water solvent, has been investigated. This convenient and clean synthesis of various tryptolines was facilitated by l-tartaric acid, a natural compound, to obtain the desired products as clear crystals. Among the four crystalline products, the most substituted tryptoline 2 showed the best inhibitory activity against EJ cells and the least cytotoxicity, with an LC50 value of 1.49 mg/mL, against brine shrimp larvae.

Laser beam melting (LBM) based on the complete-melting energy density for commercially pure titanium (CP-Ti) was investigated. Process parameters were set corresponding to the thermodynamically calculated energy density for full melting of CP-Ti. From the calculated energy density, power of 50–250 W and scan speed of 371–1855 mm/s were derived with the fixed other conditions. Microstructural study on formation of pores was conducted to understand the change in part’s density. Fundamental study with wide range of LBM process parameters, particularly based on the complete-melting energy density, could confirm the effects like high density and porous structure.

We have investigated the correlation between the microstructure and mechanical anisotropy of biomedical CoCrW alloy processed by selective laser melting (SLM). A phase analysis revealed that the as-SLM CoCrW alloy consisted of mostly the γ-fcc phase and little e-hcp phase. The as-SLM CoCrW microstructure featured the rotated cube texture, a strong texture along the building direction (BD) and a weaker texture along the front direction. To investigate the mechanical anisotropy, the external loading was applied either perpendicular or parallel to the BD (i.e., horizontal loading (⊥BD) or vertical loading (//BD), respectively). The rotated cube texture leads to a higher elastic modulus (~ 2.4 times), plastic flow stress, and microhardness in the horizontal loading. Macroscopic plastic anisotropy was elucidated by the Taylor factor analysis of polycrystalline aggregate. Strain-induced martensite transformation (SIMT) occurring in the horizontal loading ( e f = 6.9%) is responsible for significantly reduced elongation to fracture compared to the vertical loading ( e f = 32.8%). In the fatigue crack growth experiment, the threshold stress intensity range in the vertical loading is ~ 32% higher compared to the horizontal loading, leading to a retarded fatigue crack growth rate. A vertically elongated columnar granular structure due to the epitaxial grain growth along the BD results in anisotropic behavior of the fatigue crack growth.

We investigated the relationship between the microstructure and mechanical properties of additive manufactured AISI 316L steel regarding the grain aspect ratio and orientation. For this purpose, two types of specimen (vertically and horizontally built) were prepared by a selective laser melting process, and the mechanical behavior was evaluated in different tensile directions. After this, to observe the characteristic grain boundary distributions such as grain size, shape, orientation, and intergranular misorientation, electron backscattering diffraction analysis was conducted on the initial and tensile-strained specimens. The specimen with a lower grain aspect ratio showed enhanced yield and tensile strengths arising from the higher strain hardening rate relative to the specimen with higher grain aspect ratio. In addition, the material composed of grains with a higher Taylor factor showed more accumulated dislocation density during tensile deformation when compared to the material composed of grains with a lower Taylor factor, which also contributed to the increase in tensile strengths because of the enhanced strain hardening rate.

To tune the electronic and optoelectronic properties of graphene quantum dots (GQDs), heteroatom doping (e.g., nitrogen (N), boron (B), and sulfur (S)) is an effective method. However, it is difficult to incorporate S into the carbon framework of GQDs because the atomic size of S is much larger than that of C atoms, compared to N and B. In this study, we report a simple and one-step method for the synthesis of sulfur-doped GQDs (S-GQDs) via the pulsed laser ablation in liquid (PLAL) process. The as-prepared S-GQDs exhibited enhanced fluorescence quantum yields (0.8% → 3.89%) with a huge improved absorption band in ultraviolet (UV) region (200 ∼ 400 nm) and excellent photo stability under the UV radiation at 360 nm. In addition, XPS results revealed that the PLAL process can effectively facilitate the incorporation of S into the carbon framework compared to those produced by the chemical exfoliation method (e.g., hydrothermal method). And also, the mechanisms related with the optical properties of S-GQDs was investigated by time-resolved photoluminescence (TRPL) spectroscopy. We believe that the PLAL process proposed in this study will serve as a simple and one-step route for designing S-GQDs and opens up to opportunities for their potential applications.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

This study analyzed the variation of mechanical properties and its causes with increasing the laser power in the fabrication of pure titanium by selective laser melting (SLM). SLM samples were fabricated using commercially pure titanium grade 1 powder when the scan speed was 1000 mm/s and the laser power as 120, 200, 280, 360, and 440 W, respectively. As the laser power increased, the hardness and strength of the samples increased gradually. During the SLM processing, the concentrations of oxygen and nitrogen in the SLM samples were increased, which resulted in the increase of hardness and strength. The SLM equipment used in this study removed oxygen in the chamber by flowing high purity argon gas and fabricates the sample while preserving the oxygen concentration in the atmosphere to 0.2%. Evaluating the possibility of oxidation and nitriding during the SLM process by thermodynamic analysis, it was found that the process occurred under conditions in which temperature and residual oxygen and nitrogen partial pressure led to oxidation and nitriding.

Life expectancy is on the rise and, concurrently, the demand for total knee arthroplasty (TKA), which lasts a lifetime, is increasing. To meet this demand, improved TKA designs have been introduced. Recent advances in radiography and manufacturing techniques have enabled the production of patient-specific TKA. Nevertheless, concerns regarding the wear performance, which limit the lifespan of TKA, remain to be addressed. This study aims at reducing the wear in patient-specific TKA using design optimization and parametric three-dimensional (3D) finite-element (FE) modelling. The femoral component design was implemented in a patient-specific manner, whereas the tibial insert conformity remained to be determined by design variables. The gait cycle loading condition was applied, and the optimized model was validated by the results obtained from the experimental wear tests. The wear predictions were iterated for five million gait cycles using the computational model with force-controlled input. Similar patterns for internal/external rotation and anterior/posterior translation were observed in both initial and optimal models. The wear rates for initial and optimal models were recorded as 23.2 mm3/million cycles and 16.7 mm3/million cycles, respectively. Moreover, the experimental wear rate in the optimal design was 17.8 mm3/million cycles, which validated our optimization procedure. This study suggests that tibial insert conformity is an important factor in influencing the wear performance of patient-specific TKA, and it is capable of providing improved clinical results through enhanced design selections. This finding can boost the future development of patient-specific TKA, and it can be extended to other joint-replacement designs. However, further research is required to explore the potential clinical benefits of the improved wear performance demonstrated in this study.

The microstructure of a cobalt-base alloy (Co-Cr-Mo) obtained by an investment casting process was studied. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants owing to its high strength, good corrosion resistance, and excellent biocompatibility. This work focuses on the resulting microstructures arising from normal industrial environmental conditions. The characterization of the samples was carried out using optical microscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. In this study, the as-cast microstructure is an γ-Co (face-centered cubic) dendritic matrix with the presence of a secondary phase, such as M23C6 carbides precipitated at grain boundaries and interdendritic zones. These precipitates are the main strengthening mechanism in this type of alloy. Other minority phases, such as the σ phase, were also detected, and their presence could be linked to the manufacturing process and environment.

Graphite is economic and earth-abundant carbon precursor for preparing graphene quantum dots (GQDs). Here, we report a facile and green approach to produce GQDs from graphite flakes via a pulsed laser ablation (PLA) method assisted by high-power sonication. A homogeneous dispersion of graphite flakes, caused by high-power sonication during PLA, leads to the formation of GQDs following a laser fragmentation in liquid (LFL) rather than laser ablation in liquid (LAL) mechanism. The final product of GQDs exhibits the distinct structural, chemical, and optical properties of pristine graphene itself. However, graphene oxide quantum dots (GOQDs) with abundant surface oxygen-rich functional groups are readily formed from graphite flakes when high-power sonication is not employed during the PLA process. GQDs and GOQDs show a significantly different luminescence nature. Hence, selective production of either functional GQDs or GOQDs can be achieved by simply turning the high-power sonication during the PLA process on and off. We believe that our modified PLA process proposed in this work will further open up facile and simple routes for designing functional carbon materials.

Graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs) can be used in different applications such as optoelectronic and biomedical applications, respectively. Hence, the selective synthesis of GQDs and GOQDs is highly desirable but challenging. Here, we present GQDs and GOQDs selectively prepared by an easy and simple pulsed laser ablation in liquid (PLAL) method by controlling the laser wavelength. The obtained GQDs and GOQDs showed a significantly different optoelectronic nature mainly due to the existence of surface oxygen-rich functional groups (e.g. carboxyl or hydroxy groups). Also, we described a possible mechanism for the formation of oxygen functional groups during the PLAL process based on the Coulomb explosion model, which can give further insight for designing functional carbon materials.

Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.

side (HD-G) by a transgalactosylation reaction using β-galactosidase (β-gal)-containing recombinant Escherichia coli cells. The transgalactosylation reaction was carried out under high-lactose conditions for 24 hr. After 12 hr had elapsed, a new spot was identified by thin-layer chromatography (TLC) analysis, and we presumptively designated this new spot as HD-G. The n, we carried out the purification of the presumptive HD-G spot from the reaction mixture by using silica gel chromatography, and its mass was measured by electrospray ionization-mass spectrometry. The purified new spot on the chromatograph was identified a sodium adduct ion ([M+Na] + , m/z = 303.1423) of HD-G. In addition, when purified HD-G was hydrolyzed using commercially available E. coli β-gal, it was observed that a galactose molecule was released from HD-G. That is, it was demonstrated that HD-G is a galactoside derivative of HD. Finally, we confirmed that HD-G was enzymatically synthesized by E. coli β -gal as a new molecular entity. In the future, we plan to determine the minimum inhibitory concentrations of HD-G against different bacterial species. The cytotoxicity of HD-G against human skin cells will also be examined. It is expected hopefully that the galactosylation of HD would improve the functionality of HD-G.

The refining effect of electron beam melting (EBM) during the additive manufacturing of Ti products was studied by comparing unused Grade-2 commercially pure (CP) Ti powder to an equivalent powder that had been recycled 50 times. The pre-heating and blasting processes that occur during recycling were found to degrade the perfectly spherical morphology of the powder, and the concentration of O and N were also increased by about 15%. This resulted in it changing to a Grade-3 CP Ti powder; however, the purity of the final product was improved to Grade-1 CP Ti by the slight refining effect of the EBM process.

By controlling specific process conditions in the selective laser melting (SLM) of commercially pure Ti powder (Grade 1), a porous structure was fabricated to achieve a high specific surface area. Additive manufacturing was employed through SLM to control the energy density to be lower than that required for the complete melting of Ti powders by operating at a power of 80 to 480 W and a scan speed of 1750 to 10,500 mm/s. The range of the process conditions, i.e., complete melting, partial melting, and unmelted, was determined based on the observations of the microstructure parallel to the building direction. When the powders were pre-sintered and not melted under specific process conditions with an energy density lower than that required for complete melting, porous microstructures were formed with open pores. In addition, interfacial microstructural studies were conducted to confirm the presence of residual powder, which settled onto the strut, resulting in a higher specific surface area. These indicate that the SLM process can enhance the porosity, even with a specific design of lattice structures, as fluidic materials are expected to flow through the open porous structure.

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. However, a fundamental deep understanding of the formation of graphene quantum dots (GQDs) from multiwalled carbon nanotubes (MWCNTs) by PLFL has still not been achieved despite the high demand. In article number 2003538, Jeong Ho Ryu, Hyuksu Han, Kang Min Kim, and co‐workers report a mechanism for the formation of GQDs from MWCNTs by the PLFL process, through the combination of experimental and theoretical studies.

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon-based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.

Graphene quantum dots (GQDs) prepared by pulsed laser ablation in liquid (PLAL) process face barriers to commercialization due to their poor optical properties and the use of expensive carbon precursors. In this work, we report a one-step route for the preparation of N-doped graphene quantum dots (NGQDs) with excellent optical properties using a low-cost carbon precursor. The as-prepared NGQDs exhibited excellent optical properties and high quantum yield compared to pristine graphene quantum dots (0.8% → 9.1%) due to the presence of the N atoms. A possible recombination mechanism of NGQDs was investigated by time-resolved photoluminescence spectroscopy. The increase of N atoms incorporated in the GQDs resulted in an increased fraction of the short recombination lifetime from the intrinsic state. We also report a possible mechanism for the formation of the N atoms in the GQDs structure during the PLAL process, which is explained based on the plasma plume, cavitation collapse, and nitrogen precursor decomposition model.

Herein, we established a repeated-batch process for ethanol production from glycerol by immobilized Pachysolen tannophilus. The aim of this study was to develop a more practical and applicable ethanol production process for biofuel. In particular, using industrial-grade medium ingredients, the microaeration rate was optimized for maximization of the ethanol production, and the relevant metabolic parameters were then analyzed. The microaeration rate of 0.11 vvm, which is far lower than those occurring in a shaking flask culture, was found to be the optimal value for ethanol production from glycerol. In addition, it was found that, among those tested, Celite was a more appropriate carrier for the immobilization of P. tannophilus to induce production of ethanol from glycerol. Finally, through a repeated-batch culture, the ethanol yield (Ye/g) of 0.126 ± 0.017 g-ethanol/g-glycerol (n = 4) was obtained, and this value was remarkably comparable with a previous report. In the future, it is expected that the results of this study will be applied for the development of a more practical and profitable long-term ethanol production process, thanks to the industrial-grade medium preparation, simple immobilization method, and easy repeated-batch operation.

We investigated whether β-galactosidase (β-gal)-containing Escherichia coli cells could transfer a galactose to 2-phenoxyethanol, resulting in 2-phenoxyethanol galactoside (PE-Gal). PE-Gal was confirmed by liquid chromatography-mass spectrometry. In addition, we also confirmed that a galactose molecule was covalently bonded with PE during thin-layer chromatography analysis of the β-gal hydrolysate of PE-Gal. The yield for PE-Gal synthesis was about 37.5% (weight basis), which was about 7-8 times greater than that of a previous report. In addition, the concentration of β-gal (0.96 U/ml) used in this PE-Gal synthesis was about 20 times less than that in a previous report.

We evaluated a more practical and cost-effective immobilization carriers for ethanol production using the yeast Saccharomyces cerevisiae. Three candidate materials-rice hull, rice straw, and sawdust-were tested for their cell-adsorption capacity and operational durability. Derivatizations of rice hull, rice straw, and sawdust with the optimal concentration of 0.5 M of 2-(diethylamino)ethyl chloride hydrochloride (DEAE · HCl) resulted in > 95% adsorption of the initial yeast cells at 2 hr for DEAE-rice hull and DEAE-sawdust and in only approximately 80% adsorption for DEAE-rice straw. In addition, DEAE-sawdust was found to be a more practical carrier for immobilizing yeast cells in terms of operational durability in shaking flask cultures with two different speeds of 60 and 150 rpm. Furthermore, the biosorption isotherms of DEAE-rice hull, -rice straw, and -sawdust for yeast cells revealed that the Qmax of DEAE-sawdust (82.6 mg/g) was greater than that of DEAE-rice hull and DEAE-rice straw. During the 404-hr of continuous column reactor operation using yeast cells immobilized on DEAE-sawdust, no serious detachment of the yeast cells from the DEAE-sawdust was recorded. Ethanol yield of approximately 3.04 g/L was produced steadily, and glucose was completely converted to ethanol at a yield of 0.375 g-ethanol/g-glucose (73.4% of the theoretical value). Thus, sawdust is a promising practical immobilization carrier for ethanol production, with significance in the production of bioethanol as a biofuel.

It is experimentally well known that mechanical properties of the material depend on crystallographic texture distribution which varies depending on deformation history. When the material deforms at several stages, it is not easy to follow up the effect of prior deformation on the final texture of the material. In the present study, the effect of deformation history on texture evolution during equal channel angular pressing (ECAP) of FCC polycrystalline metal like AA1050 is investigated by the finite element method and polycrystal plasticity model based on full constraints Taylor model. The texture evolution during the multi-pass ECAP is simulated with the initial textures determined by three virtual specimens prepared by the fully annealed, extruded, and flat-rolled materials. By comparing the pole figures and orientation distribution functions, the effect of prior deformation histories on the texture evolution is numerically studied according to the routes A and C up to four passes across the thickness of the specimen. For the extruded specimen, it is not enough to wipe out the trace of the initial textures originated from the extrusion even after four passes. For the rolled specimen, strong development of the rotated simple shear texture readily occurred with the rotation about the transverse direction of the ECAP die. This study indicates that it is necessary to control the initial texture properly for achieving a desired mechanical property.

We investigated ethanol production from glycerol after screening of the yeast Pachysolen tannophilus ATCC 32691. For yeast to produce ethanol form glycerol, it is important that aeration is finely controlled. Therefore, we attempted to produce ethanol using a surface-aerated fermentor. When 880 ml of YPG medium (1% yeast extract, 2% peptone, 2% glycerol) was used to produce ethanol, the optimal aeration conditions for ethanol production were a surface aeration rate and agitation speed of 500 ml/min and 300 rpm, respectively. In a fed-batch culture, the maximum ethanol production and the maximum ethanol yield from glycerol (Ye/g) was 5.74 g/l and 0.166, respectively, after 90 hr using the surface-aerated fermentor.

The main objective of this study is to simulate deformation induced anisotropy during the upsetting of commercially available pure aluminum AA1050 after being processed by the equal channel angular extrusion (ECAE) process including the friction effect. A Taylor-type polycrystalline constitutive model was adopted to investigate the effects of texture evolution and deformation heterogeneity during the ECAE and upsetting. In order to save computation time, a decoupled analysis between the crystal plasticity model and finite element method for the multi-pass ECAE and a fully coupled analysis for the subsequent upsetting process were conducted. The rigid-viscoplastic finite element analysis of the ECAE was carried out to determine the history of velocity gradient during the ECAE process in order to identify the effects of the processing routes A and C on texture evolution. The calculated history was applied to the crystal plasticity model to obtain the crystallographic texture distribution. Then, a finite element analysis based on the Taylor model was conducted for prediction of the anisotropic behavior of the three-pass ECAEed specimens which was obtained by applying the ECAE of the aluminum alloy AA1050 with routes A and C, respectively. For this analysis, algorithms for the data transfer of Euler angles and hardness were developed and implemented into the program. The good agreement between the measured and simulated deformed shapes indicates that the proposed simulation technique with the data transfer algorithms can be used effectively to simulate deformation induced heterogeneity during the bulk forming process.