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Process optimization for the selective laser melting (SLM) of the Fe-10Cu alloy was performed to obtain defect-free parts based on the energy density for thermodynamically complete melting. A microstructural study was conducted for the corresponding energy densities that focused on identifying defect formation mechanisms. A range of defects formed via by diverse mechanisms, such as lack of fusion, balling, shrinkage and the key-hole effect, were characterized, including mixed zones. The process range in which these defects were not formed could be suggested as the optimal conditions for SLM of the Fe-10Cu alloy. In this study, a laser power below 320 W, a scan speed below 1523 mm/s and an energy density under 15.56 J/mm3 were indicated to be the optimum process conditions for SLM of Fe-10Cu alloy to avoid micro-cracks from shrinkage, balling and rounded pores from the key-hole phenomenon.

The effects of the electron beam (EB) continuity on the microstructures and mechanical properties of titanium lattice structures with produced by EB additive manufacturing were studied. Continuous line and discontinuous spot scans were applied for the EB continuity. The porous structures produced with the continuous line scans had lower defect densities than those produced with discontinuous spot scans. Most defects of the continuous line scans had spherical morphologies, whereas non-spherical defects formed in the porous structure produced with discontinuous spot scans because of the availability of sufficient heat for melting the powder. The microstructures were composed of an α-titanium matrix, martensitic α′ phases, and elongated FeTi4 phases on the grain boundaries. Furthermore, the atom probe tomography results showed that the FeTi4 phase had a network structure with a diameter of 5 nm after the continuous line scan, which enhanced the compressive strength. The compressive strength and elastic modulus of the porous structures produced with the continuous line scan were more than 400 MPa and 11 GPa, respectively. Despite the high porosity, continuous line scans are preferable for achieving high compressive strengths with low elastic moduli for biomedical devices.

To improve the reliability and functionality of medical commercially pure titanium (CP-Ti) part fabricated by electron beam additive manufacturing (EBAM), we studied a post-treatment like cyclic heat treatment. For uniform microstructure by inducing the repetitive nucleation during phase transformation, the specimens were repeatedly heat-treated from 25 °C to 1,000 °C in Ar atmosphere. Microstructural and mechanical studies were carried out with as-built specimen and heat-treated specimens for 1, 3, and 5 cycles. Grain size was uniformly refined from 61.2 μm to 19.4 μm, in addition the elastic modulus was lowered from 136.8 GPa to 64.4 GPa. Particularly, the martensitic α′′ phase with orthorhombic structure in few tens of nm size was observed after cyclic heat treatment which was considered to reduce the elastic modulus. Although the yield and tensile strengths were slightly decreased after cyclic heat treatment, it was still higher value compared with the wrought CP-Ti part. For the patient-specific CP-Ti part, consequently, the cyclic heat treatment could be considerable post-process without any mechanical process.

The defects, microstructure, and mechanical properties of Inconel 718 superalloy fabricated by electron beam additive manufacturing with different focus offsets were investigated. The samples built with a low focus offset exhibited numerous micro-voids of 10 μm and a columnar grain microstructure with a strong [001] texture in the built direction (BD). Unmelted powder and macro-voids of approximately 200 μm were observed at higher focus offsets, and the columnar grain width decreased from 600 μm to 150 μm with increasing focus offset. γ׳ precipitates with a length of 10 nm developed parallel to the BD, while γ״ precipitates with length of 4 nm formed perpendicular to the BD owing to the higher thermal conductivity. Samples built with a low focus offset exhibited intergranular fractures, while samples built with a high focus offset exhibited brittle fractures because of the unmelted powder and macro-voids. Samples built with focus offsets of 9 mA and 12 mA exhibited the highest tensile strengths of 1.3 GPa and 1.0 GPa at room temperature and high temperature, respectively. γ׳/γ״/γ׳ and γ׳/γ״/γ׳/γ״/γ׳ sandwich structures on the columnar γ grains developed parallel to the BD in the as-built samples because the preheating process between consecutive layers increases the dwelling time in the temperature range facilitating the δ → γ״ and δ → γ׳ phase transformation. The volume fractions and size of the γ׳ and γ״ precipitates increase with the focus offset owing to the prolonged dwelling time; however, micro-voids formed and unmelted powder was present because of insufficient heat of fusion.

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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.

In this study, the selective electron beam melting (SEBM) process was used to fabricate Inconel 718 superalloy, and their microstructures and creep resistances were investigated. The proper SEBM condition ensuring a relative density higher than 99.9% was found in electron beam current range of 24–30 mA at a scanning speed of 4500 mm/s and a preheat temperature of 1025 °C, from which the SEBMed Inconel 718 exhibited an unidirectional columnar grain microstructure with a strong texture along building direction. It was suggested that the local thermal condition during solidification after SEBM facilitates a continuation of epitaxial growth of crystals on layer beneath. The γ″ precipitates formed in the as-built condition regardless of focus offset, and their size increased with increasing focus offset from 1 to 12 mA. The creep rupture life of the as-built sample fabricated with focus offset of 12 mA showed 2 times longer than that of conventional forged Inconel 718 subjected to full heat treatment under creep condition of 650 °C/700 MPa. EBSD analysis on the crept samples indicated that strain accumulation was significant at the porosities and the high-angle grain boundaries. Additionally, the grain boundaries inclined to loading axis were more damaged during creep. The γ″ particles were occasionally sheared by matrix dislocations with Burger vector of a/2 , without leaving stacking faults behind. The enhanced creep resistance of SEBMed Inconel 718 superalloy can be attributed to the columnar microstructure with a strong texture and the high density of dislocations resulted from strong interaction with the γ″ particles.

The mechanism of extrusion and intrusion formation in Co–Cr–Mo–N alloys during fatigue deformation was investigated. In particular, we focused on the role of the strain-induced martensitic transformation (SIMT), which is the transformation of the metastable γ face-centered cubic (fcc) phase into a stable e hexagonal close-packed (hcp) phase at room temperature because of the gliding of Shockley partial dislocations in the γ-phase matrix. We found that the SIMT also plays a crucial role in the formation of extrusions and intrusions. Further, the morphology of the extrusions and intrusions formed in the Co–Cr–Mo–N alloy specimens was very different from that seen in other fcc alloys. The extrusions and intrusions were formed by the gliding of perfect dislocations with a Burgers vector of perfect dislocation on the basal plane of the e-hcp phase. This suggests that the e-phases introduced by the SIMT can deform readily.

Biomedical Co–Cr–Mo (CCM) alloys have been commonly used for artificial hip and knee joint prostheses, but a need to improve their biomedical inertness and wear resistance has become widely recognized. The mechanical behavior of CCM alloys is dominated by strain-induced martensitic transformation (SIMT), which causes crack initiation during plastic deformation but dramatically enhances the wear resistance in practical use. To develop more reliable CCM alloys it is essential to clarify the factors affecting the occurrence of SIMT. In the present study we have focused on the effect of annealing twin boundaries (ATBs) on SIMT behavior. We have analyzed in detail the substructures near a parallel pair of ATBs after deformation under a stress preferential for slip parallel to the ATBs. Preferential formation of e-hexagonal close-packed (HCP) phase at ATBs in metastable γ-face-centered cubic (FCC) phase was found by both scanning electron microscopy with electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). High resolution TEM images indicated that thickening of the e-HCP phase does not proceed regularly on every second atomic plane, which would form perfect e-phase HCP structure, but irregularly leaving a high density of stacking faults. Furthermore, the thickness of the e-HCP phase was found to be different at ATBs on the two sides of the twin. The difference was attributed to the internal stress due to strain incompatibility at the ATBs on the basis of residual stress analysis by the EBSD–Wilkinson method and phase-field simulation of solute segregation at ATBs.

The influence of aging treatment on the microstructure, mechanical and electrical properties of Cu-Be alloy for connector material applications was investigated. The properties of mechanical strength and electrical conductivity were found to increase with increasing aging temperature. By the way, SEM/EDS and TEM analysis exhibited that beryllides precipitation (CoBe and NiBe) with a size of 50 nm were distributed in grains. It was, therefore concluded that these beryllide precipitates improved the mechanical strength and also it was favor in increasing of electrical conductivity.

The effect of thermal heat treatment on the mechanical and electrical properties of Cu–Ag alloys was investigated. The homogenization heat treatment leads to an increase in tensile strength and a decrease in electrical conductivity due to dissolution of Ag into copper matrix. Also, it is shown that electrical conductivity of as-cast Cu–Ag alloys decreases with increasing Ag content. In contrast, the aging heat treatment gives rise to increase both the tensile strength and electrical conductivity because the Ag solute diffuses out from copper matrix during aging heat treatment. Therefore, it can be mentioned that the electrical conductivity of Cu–Ag alloys depends on Ag solute in copper matrix. Also, aging treatment is favorable to acquire high strength and high electrical conductivity.

A transmission control cable connects the transmission control arm and the control lever mechanically and transfers control effort exerted by a driver to the transmission. It also transfers vibration generated by the engine to the passenger room through mechanical connection. To understand vibration and noise transfer mechanism and to further find a way to suppress the transmission of vibration effectively, a dependable dynamic vibration model is a necessity. A vibration model for a transmission control cable is developed and a simulation study has been conducted to obtain mode frequencies and a transmittability. The resonance frequencies obtained by an harmonic analysis is compared with the noise level measurement data. The measurement agrees with the simulation result thus ensures the reliability of the model.

An automotive windshield wiper system is modeled mainly for vibration analysis purpose. The model is composed of solid links, ideal joints, imperfect joints to simulate unavoidable manufacturing defects and bushings having stiffness, contact between a wiper blade and a wind screen glass, friction, a spring and an actuator. Main stream of wiper dynamics analysis has been obtaining a closed form of system of equations using Newton`s or Lagrange`s formula and doing a numerical simulation study to understand and predict the behavior of it. However, the modeling process is complex since a wiper system is of multibody and a contact problem occurs. When imperfection, such as dead zone of a joint and stiffness of a rubber bushing, should be included, the added complexity makes the modeling difficult. Since the imperfection is understood as main cause of problematic vibration, the dynamics model of a wiper system aiming vibration analysis should include such unavoidable manufacturing defects in the model. An open form of dynamic model of a automotive windshield wiper system with imperfect joints using a commercial software is obtained and a simulation analyssis is conducted for vibration reduction study.

In accordance with environmental regulations on refrigeration technology, the commercial A1100 alloy condenser tube that has widely been used in CFC and HCFC refrigerant systems and operated at a low working pressure (10–30 bar) was inappropriate to the eco-friendly CO 2 refrigerant systems which possess a high working pressure (60–80 bar) due to the low mechanical properties. As a result, the stiffness of the conventional 1000 series alloys might not be appropriate in this requirement. The present study is mainly aimed at developing condenser tube material such as A3003 alloy for the application of eco-friendly refrigerants with higher working pressure rather than for conventional CFC and HCFC refrigerants. The mechanical properties and pressurized strength of condenser tube are greatly affected by the coarse grains, which grow during the brazing process. According to the pressurized testing, A3003 alloy is more suitable than A1100 alloy when the condenser tube is applied to eco-friendly refrigerants usage because A3003 alloy can be durable in a heat exchanger which requires high working pressure.

This paper analyzes if the rapidly increasing cyber universities` remote education provides services based on web accessibility standard and suggest the direction to reduce information difference between people. It selected 10 cyber universities recognized by the government and analyzed the application situation of the web accessibility using` A-Prompt`, an evaluation and analysis tool for web accessibility focusing on factors that can be evaluated technically. It also compared it with cyber universities remote education web accessibility result performed in 2006 to confirm if the accessibility is improved according to `web contents accessibility instruction (KWCAG) 1.0. The result shows that the items such as the use of text and the support of supplementary explanation tool have improved. But it was analyzed that it is difficult for people to use web contents provided by domestic cyber universities. So the educational contents` accessibility application must be considered to solve such problems and publicize the remote education.

Various TiO2/SiO2 composite nanoparticles were prepared by vapor phase hydrolysis of Titanium Tetraisopropoxide (TTIP) and Tetraethylorthosilicate (TEOS) in a tubular reactor heated by electrical furnace by changing the methods of reactant mixing, the molar ratio of the precursors and the set temperature of the furnace. These variables affected the average size and the bulk composition of the particles as well as their morphological and crystalline structures. The morphological structures of the particles were reconfirmed as T-S, S-T and T/S as in the previous study. Various correlations were obtained between the molar ratio of the precursors, and the size, the composition and the TiO2 main peak intensity of the particles as a parameter of the mode of reactant mixing. In general, it was found that high content of silicon constituent showed translucent envelopes surrounding primary particles, which increased the dispersion diameter of the particles, reduced the thermal stability, retarded the anatase-to-rutile transformation and the initial photocatalytic degradation of phenol in an aqueous solution.

In this paper, we describe a new speech/non-speech classification method that improves the endpoint detection performance for speech recognition in noisy environments. The proposed method uses multiple features to increase the robustness in noisy environments, and the classification and regression tree (CART) technique is applied to effectively combine these multiple features for classification of each frame. We evaluate the performance of the proposed method by conducting speech/non-speech classification experiments on noisy speech. We also investigate the importance of various features on speech/non-speech classification in noisy environments In particular, the proposed method is applied to the endpoint detection algorithm for isolated speech recognition of a voice-dialing cellular phone. We simulate the speech recognition experiments in various noise environments, and the effects of the proposed method on speech recognition performance are evaluated.

In the present study, in order to find out an grain refinement mechanism, 0.1wt.% Al-10wt.%Ti master alloy was added into A3003 alloy melt contained in graphite crucible and in alumina crucible, and then the melt holding time at 750°C was systematically changed from 1 min up to 120 min. It is interesting to note that the grain refinement and fading phenomena remarkably depend on the crucible material. The fading effect in the specimens using alumina crucible can be explained as the result of TiAl3 phase dissolution into molten aluminium matrix. In the specimens using graphite crucible, the grain refinement was occurred gradually with increasing holding time. It was suggest that the continuous grain refinement is due to transition of refinement mechanism from TiAl3 phase to TiC phase. It can be mentioned that the TiC formed from titanium and carbon solute in the aluminium melt, which came from the Al-10Ti alloy and the graphite crucible.