Eco-Materials Processing & Design VI

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Authors: Santiago Visbal, Joaquín Lira-Olivares, Tohru Sekino, Koichi Niihara, Byung Kyu Moon, Soo Wohn Lee
Abstract: Microstructure and mechanical properties of Al2O3-TiO2-SiC nanocomposites were studied. To improve the mechanical and tribological properties of alumina, nano-sized TiO2 and SiC powders were dispersed. Spark Plasma Sintering (SPS) technique, at 1400°C, 50 MPa for 5 minutes, was applied for the densification of Al2O3-TiO2-SiC nanocomposites. Characterization of Al2O3- TiO2-SiC nanocomposites was carried out using Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), X-ray diffractometer and EDX. Fracture toughness and Vickers hardness were estimated by indentation technique. These experimental results on mechanical properties of Al2O3-TiO2-SiC nanocomposites indicated that they can be a potential material with high hardness and high fracture toughness to be used as femoral head in total hip joint replacement.
Authors: Wei Chang Xue, Xuan Yong Liu, Xue Bin Zheng, Chuan Xian Ding
Abstract: A new bioceramic coating based on wollastonite was prepared by plasma spraying. The coatings exhibited good mechanical properties. The bond strength of the coating on substrate was about 40 MPa, which is higher than that of HA coatings used in orthopedics and dentistry. The bioactivity of wollastonite coatings was evaluated in vitro and in vivo. After immersed in simulated body fluid, a bone-like apatite layer was formed on the surface of wollastonite coatings. Osteoblast could survive and proliferate on the surface of coatings. After implanted in dog’s cortical bone, histological observation demonstrated that bone tissue could extend and grow along the surface of wollastonite coatings. The coating bonded directly to bone without any fibrous tissue, indicating good biocompatibility and bone conductivity. The wollastonite coatings also showed good bone inductivity property, inducing new-bone formation on their surface after implanted in marrow. The results obtained indicated that the plasma-sprayed wollastonite coatings possessed good mechanical properties and excellent bioactivity in vitro and in vivo. It appears that a wollastonite coating may be suitable for the repair and replacement of living bone, especially for load-bearing situations.
Authors: Ying Zhao, Tian Ying Xiong, Hua-Zi Jin, Li Bin Wang, Tie Fan Li
Abstract: A layer of amorphous thick anodic oxide film was formed on Ti6Al4V substrate after anodization, and its thickness achieved 30-40µm. After immersion in SBF, anodized sample and substrate indicated different corrosion resistance. According to icorr, Rp and Ecorr, the concerned experimental results of potentiodynamic polarization curves, the anodic oxide film provided effective corrosion protection, which could be attributed to its relatively uniform, smooth, compact and intact microstructure. And the results of total immersion test also proved the protective role of the anodic film.
Authors: Rak Joo Sung, Seung Ho Kim, Takafumi Kusunose, Tadachika Nakayama, Tohru Sekino, Koichi Niihara
Abstract: Silicon nitride with various amount of AlN as a sintering aid was sintered by a hot press method. Densified silicon nitrides were obtained, and it was found that the mechanical and wear properties were dependent on the contents of AlN. The effect of a/b phase on the mechanical and wear properties of silicon nitride was investigated. The properties were changed depending on the amount of a/b phase. In the brittle materials, tribological behaviors were dependent on the microstructure as well as hardness and fracture toughness. We focus on the relationship between the microstructure and mechanical/wear properties of silicon nitride including AlN additives.
Authors: Seung Ho Kim, Tohru Sekino, Koichi Niihara
Abstract: Tribological behaviors of Al2O3/SiC nanocomposites were found to be related to the amount of nanosized SiC and initial Hertzian contact stress. As the applied load increased, the wear volumes of Al2O3/SiC nanocomposites slightly increased, but that of monolithic Al2O3 increased rapidly above 50 N. Tribological behavior of monolithic Al2O3 was transited from mild wear to severe wear.
Authors: Sung Sic Hwang, Sang Whan Park, Seong Jai Cho, Dong Bok Lee
Abstract: The contact fracture behaviors of fine-grained Ti3SiC2 and coarse-grained high purity Ti3SiC2 are examined by the Hertzian indentation and Vickers indentation technique. The Vickers hardness of bulk Ti3SiC2 is as low as 5.3~6.3 Gpa, and the Hertzian contact stress-strain curves for Ti3SiC2 deviate much from linearity, which resembles the fracture behavior of a ductile metal rather than a brittle ceramic. The contact damages by both Vickers indentation and Hertzian indentation reveal a fairly good plastic deformation nature of Ti3SiC2. Un-reacted TiCx in fine-grained Ti3SiC2 may impede the plastic deformation by slip along basal plan inside Ti3SiC2 grain, making Ti3SiC2 less plastic under loading.
Authors: Sung Park, Jae Chun Lee, Jung Uk Seo, Ju Hyeon Lee
Abstract: ZnO nanopowders with an average grain size of 30nm were prepared by a solution combustion method with various sintering temperatures (100-1000o C). The optical properties of the ZnO nanopowders were investigated in the temperature range of 14-150K in air. Based on the results of XRD, Photoluminescence, and excitation spectra, the ZnO powders showed wurtzite single phase with UV-blue light emitting. Deep level defects such as oxygen vacancies and Zn interstitials were not observed from the ZnO powders sintered up to 700 o C. However, these defects were observed as the sintering temperature was increased up to 900 o C. This seems to be due to the generation of oxygen vacancies and zinc interstitials. Furthermore, the blue light intensity was doubled when the synthesized ZnO powders were sintered at 700 o C. This might be very useful for high efficiency photocatalysts and the blue light emitting phosphors of displays such as field emission displays and plasma display panels.
Authors: Yo Seung Song, Il Seok Park, Ju-Woong Jang, Deuk Yong Lee, Se Jong Lee
Abstract: Hertzian cyclic fatigue properties of the glass-infiltrated alumina and spinel were evaluated using a WC sphere of radius of 3.18 mm in exact in vitro environment (artificial saliva) at contact loads from 200 N to 1000 N to investigate indentation damage and strength degradation. At 200 N, no strength degradation was observed up to 106 contact cycles. As the load increased from 200 N to 1000 N, the reduction in strength was found when the transition from ring to radial cracking occurred. The degree of strength degradation after critical cycling was more pronounced probably owing to the chemical reaction of the artificial saliva with the glass phase along the radial cracks introduced during the large numbers of contact cycles.
Authors: S.H. Lee, Byung Hak Choe, Young Pyo Kim, Woo Sik Kim, Y.T. Ko, Je Hyun Lee, Ung Yu Paik
Abstract: This study presents a probabilistic methodology for estimation of the remaining life of pressurized pipelines containing active corrosion defects. A reliability assessment was carried out using extreme value distribution of the corroded defects instead of the already published failure pressure model like NG18 or ASME B31G. The failure probability of pipelines depends on the number of corroded defects, and it was calculated directly as the area exceeded a defined LV(Limited Value of corrosion depth). The remaining life of pressurized pipelines can also be estimated by the PDF of extreme value distribution as calculating the exceeded area with a defined failure probability.
Authors: Hwang Gu Lee, Dong Jin Kim, Jeong Whan Han, Byung Don You, Ji Young Byun
Abstract: Magnesium alloys have been well known as active metals. Thus, magnesium alloys in molten state must be handled with extreme care during melting and casting. In this study, water model experiments and numerical analyses were carried out to optimize a pipe flow that can transport magnesium alloys in molten state safely from melting to casting furnace. Especially, during a transportation of molten magnesium alloys, a flow pattern in a pipe becomes important, because the interface between air and melt can be the source of the metal oxidation, and therefore, an air/melt interface area must be minimized. For these purposes, two vessels connected with a long pipe having two elbows with different diameters and radii of the curvature were simulated as melting and casting furnace for magnesium alloys. Optimized conditions with minimized air/melt interface area for the melt transportation were discussed in several pipe configurations.

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