Materials Science Forum Vols. 449-452

Abstract: The fabrication parameters for highly ordered nanopore arrays formed by self-organized anodization on aluminum have been investigated. To fabricate ordered nanopore arrays in alumina layer a two-step anodization process was used in oxalic acid solution. The regular nanopore arrangement, interpore distance and pore diameter in alumina surface were strongly dependent on the applied potential at anodization. The interpore distance and pore diameter increased with anodic applied potential, and hexagonally ordered pore arrangements in alumina were obtained by anodization at 40V. For the effects of the heat treatment of aluminum substrate on size of domains with same pore orientation, the domain size increased with increasing annealing time.

Abstract: In this study, photocatalyst-coated glass beads by CVD, N-substituted TiO2 for visible light activation, plastic optical fiber bundle and treated Ti plate were considered as ‘Ecomaterials’ for the potential use in photocatalytic environmental purification system. Each material was carefully prepared and characterized to use in real system either by itself or together for a specific application. The absorption edge of the obtained TiON was ca. 530 nm and the presence of photocatalytic activity of the material under visible light was evidenced.

Abstract: TiO2 thin films were prepared by RF sputtering on Si wafer to investigate hydrophilicity and bactericidal effects by using AFM, XRD, standard plate count method and wetting angle measurement. Experimentally, the survival rate of E. coli was above 74% and the wetting angle of water for the 30 min UV illuminated films was 4.2o. It was found that the bactericidal efficiency was closely related to the large specific surface area caused by the roughness, however, hydrophilicity was governed by the surface defective sites rather than the roughness.

Abstract: Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or􀀂 both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 µm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (Pf/Ff), where Pf and Ff stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer’s solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.

Abstract: Effects of alloying elements on elastic moduli (Young’s moduli) of Ti-Nb-Ta-Zr system alloys for biomedical applications were investigated. In this case, Ti-30Nb-10Ta-5Zr which is the simplified chemical compositional alloy of Ti-29Nb-13Ta-4.6Zr for biomedical applications has been selected as the basic alloy composition. Each alloying element content of Ti-Nb-Ta-Zr quaternary alloys was varied independently. Nb content was varied from 0 through 40 mass % by eight levels. Ta content was varied from 0 through 20 mass % by five levels. Zr content was varied from 0 through 10 mass % by five levels. Every alloy was fabricated by powder metallurgy processing, followed by forging. Ti-30Nb-10Ta-5Zr with single
phase, which is a basic alloy composition, shows the lowest Young’s modulus.  phase precipitation in
phase has much greater effect on increasing Young’s modulus than  phase precipitation in Ti-Nb-Ta-Zr quaternary alloys.

Abstract: Using Ti-40mass%Ta-0, -4, -8 and -12mass%Sn alloys, the effect of Sn addition on phase constitution in the solution treated and quenched state and isochronal heat treatment behavior is studied by electrical resistivity and Vickers hardness measurements and X-ray diffactometry. To confirm shape memory effect of some of these alloys, shape-recovery test was also performed. Orthorhombic martensite,
” was identified in Ti-40Sn-0 to 8Sn alloy quenched from 1173K, while  phase was identified in STQed Ti-40Ta-12Sn alloy. On isochronal heat treatment, increases of resistivity at LN and resistivity ratio were observed in only 8Sn alloy, because these increases are due to reverse-transformation of
” to  phase. From result of shape recovery test, shape memory effect was observed in Ti-40Ta-4 and 8Sn alloys

Abstract: . An investigation of wear and bioconductivity characteristics of oxidized Ti-29Nb-13Ta- 4.6Zr is presented. Experimental results showed that oxidation treatment at 400oC for 24h in air results in the formation of a hard layer on the surface of the alloy, which greatly benefits its wear resistance. Calcium phosphate (Ca-P) phase was found to grow on the oxidized and alkali treated Ti-29Nb-13Ta-4.6Zr alloy samples when they were immersed in a protein-free simulated body fluid or fast calcification solution.

Abstract: Microstructures of the interface between plasma-spray coated hydroxyapatite (HAp) and Ti-alloy substrate have been investigated mainly by means of transmission electron microscopy. The results obtained are as follows; HAp coating exhibits a high crystallinity. The interface of HAp/Ti-alloy is winding at an interval of about 100µm and thickness of HAp coating is about 50µm. Al2O3 abrasives remained in both HAp coating and Ti-alloy substrate around the interface. Amorphous phase was not observed at the interface. The grain size of Ti-alloy in the vicinity of the interface is about 10 to 100nm in diameter, while that far from the interface is about 3µm in diameter. Miniaturization of Ti-alloy grain around the interface was occurred by plasma spraying. There is no specific crystallographical orientation relationship between HAp and Ti-alloy at the interface, indicating bonding of the interface is essentially mechanical one such as an anchor effect.

Abstract: Reciprocal Tribocontact has been manifested to be responsible for the certain attrition of artificial components in dental fields. But confusion on the aspects of friction and wear pattern was found between fretting and sliding, the two items often emerging in reports about friction and wear of biomaterials, due to the ambiguity on definition. By refining the definition of fretting with partial slip concept, this work compared friction and wear behaviors of three dental alloys under fretting and sliding conditions. Results indicate that friction force waveform and surface damage topography created by fretting quite differs from by sliding. The curve of friction force vs time under fretting is of nearly perfect sine waveform; some micro disturbance occurs on the peaks and valleys of the waveform while the amplitude is big enough. Wear patterns from fretting consist of a central stick region, a surrounding slip region and sometimes crack between the two regions, but wear patterns from sliding are of linear tracks running through the entire scar, scraped trace or severe surface deformation.

Abstract: Biological hard tissues show preferential alignment of the c-axis of biological apatite (BAp) crystallites depending on the shape and stress distribution in vivo, but apatite-base bioceramics developed for bone grafting have no preferential BAp orientation. Thus, the crystal orientation was controlled for developing novel bioceramics with apatite (Ap) texture similar to biological hard tissues. Since cortical portion in a bovine femur shows a one-dimensional orientation along the longitudinal direction of long bone, the effect of heat treatment on Ap orientation was investigated in the femur bone as a starting material. Heat treatment was performed first at 600°C for 1h to remove organic constituents and subsequently at each temperature between 700°C and 1300°C. Crystal orientation and texture of BAp were measured by the micro-beam X-ray diffractometer. Size of BAp crystallites increased remarkably after a heat treatment even at 600°C for 1h and a great amount of pore remained in the Ap ceramics in exchange for the organic constituents. Several Ap grains were surrounded as a group by the pores, but additional heat treatment in a temperature range up to 900°C reduced the number of Ap grains in the group, and finally became a single grain region at 1000°C. Pore density decreased with increasing annealing temperature, especially above 1000°C. One-dimensional preferential alignment of the c-axis in Ap maintained during all the heat treatment and the degree increased with increasing annealing temperature because a lot of low-energy low angle boundaries against the c-axis existed in the starting material and preferentially remained in the synthesized Ap ceramics. It was therefore concluded that adequate heat treatment of bovine femur can give the preferential crystal orientation in Ap ceramics.