Preparation of Self-Standing, Submillimeter-Thick Porous Titania Films with Anatase Nanocrystallites Using Evaporation-Induced Self-Assembly

Self-standing transparent submillimeter-thick (∼0.34 mm) mesoporous titania films were prepared using the evaporation-induced self-assembly (EISA) of a triblock copolymer template and titanium tetraethoxide. Performing EISA at low temperature and low humidity improved the transparency and continuity of the films. As synthesized films had a well-defined hexagonal mesostructure and the existence of both amorphous titania and anatase nanocrystallites (2 nm) was confirmed. The films that were calcined at 400°C were composed of anatase nanocrystallites (14–16 nm) and had a BET surface area of 90 m² g⁻¹ with 13-nm pores. The films were characterized using XRD, FE-SEM, TEM, and N² adsorption–desorption measurements. An erratum to this article can be found at     

Relationship between yield ratio and the material constants of the Swift equation

The relationship between the yield ratio and the material constants,b andN, of the Swift equation for hotrolled low carbon steels has been established. The yield ratio calculated by using the Swift equation agrees well with an experimentally obtained yield ratio. It was found that the yield ratio decreases with an increasing value ofN or with a decreasing value ofb. It was also found, however, that high yield strength is associated with small values of bothb andN. Therefore, to obtain both high yield strength and low yield ratio, a detailed microstructural control is needed to determine the optimum values ofb andN.     

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB₂, B₄C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB₂ or B₄C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB₂ compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB₂ reactant powder was higher than that of the composite made from B₄C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB₂ reactant powder was better than that made from B₄C.     

Microstructures and tensile behavior of carbon nanotube reinforced Cu matrix nanocomposites

Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to improve the mechanical performance of monolithic materials. However, the CNT/metal nanocomposites have shown lower strength than expected. In this study, the CNT reinforced Cu matrix nanocomposites were fabricated by spark plasma sintering (SPS) of high energy ball-milled nano-sized Cu powders with multi-wall CNTs, and followed by cold rolling process. The microstructure of CNT/Cu nanocomposites consists of two regions including CNT/Cu composite region, where most CNTs are distributed, and CNT free Cu matrix region. The stress–strain curves of CNT/Cu nanocomposites show a two-step yielding behavior, which is caused from the microstructural characteristics consisting of two regions and the load transfer between these regions. The CNT/Cu nanocomposites show a tensile strength of 281 MPa, which is approximately 1.6 times higher than that of monolithic Cu. It is confirmed that the key issue to enhance the strength of CNT/metal nanocomposite is homogeneous distribution of CNTs.     

Influence of feedstock preparation on ceramic injection molding and microstructural features of zirconia toughened alumina

Feedstocks for ceramic injection molding of ZTA containing 90 vol.% of sub-μm alumina and 10 vol.% of zirconia nanopowder were prepared by different processing techniques. Feedstocks were prepared by mixing in a sigma-blade kneader and subsequent homogenizing by twin-screw extrusion or shear roll compaction. Two other feedstocks were previously bead milled and subsequently processed by the same procedure. Compounding technology strongly influences the injection molding behavior and microstructures of the final product. Despite higher energy input of the shear roll compactor, powder agglomerates cannot be completely avoided. Pre-milling is effective to disperse and deagglomerate ceramic powders. Injection pressures of feedstocks from pre-milled powders were about 200 bar lower compared to pressures needed for non-milled feedstocks. Present feedstock preparation methods are feasible to produce homogeneous feedstocks, which strongly influence microstructures. In order to produce high solid loaded sub-μm/nm feedstocks, processing methods, pre-treatment and solid content have to be carefully chosen.     

The effect of a multistep deep-drawing process with circular and rectangular shapes on the deformation of AZ31 magnesium sheets

This study has mostly focused on the forming limit, microstructural change, and anisotropy that arise from rectangular and circular deep drawing of magnesium sheets. Moreover, this study predicts the change in the material thickness and the forming depth at the first forming process that produces the rectangular cup by the deep drawing of the rectangular blank. Further, by using the rectangular cup that is formed by the first forming process, when the circular and square cups in the rectangular cup are simultaneously manufactured in the so-called second forming process, the effect of the clearance between the die and punch on the change in the product thickness according to forming depth associated with microstructural analysis is investigated. The forming temperature is optimized to maximize formability. The results obtained in this study are utilized as data for predicting the die clearance and the change in the thickness.     

Influence of low temperature working on microstructure and mechanical properties of AI-7Si-(Fe) alloys

Changes in the microstructure and mechanical properties of Al-7Si-(Fe) alloys by low temperature working have been investigated. The size and shape of eutectic Si and intermetallic AlSiFe compound were controlled by the low temperature working process. This process consisted of repeated cold working at 77 K and recovery treatment at 793 K. By applying this process to the Al-7Si-1Fe alloy, the eutectic Si and acicular Fe compound(β-AlSiFe) phases were broken down to the size of 2-3 μm, with spherical shape. The refined particles were uniformly distributed, and a fine microstructure was obtained. The strength and elongation of Al-7Si-1Fe alloy increased as the temperature was lowered due to the microstructural refinement. This elongation was well reflected in the fracture surface.     

Effect of precipitation from tweed matrix on the mechanical properties in a metastable beta alloy of Ti-15-3

The effects of aging treatment on the microstructures and mechanical properties of a metastable beta titanium alloy Ti-15-3 (Ti−15V−3Al−3Sn-3Cr) have been investigated with hardness measurements, tensile test, and optical and electron microscopy. Precipitate-free beta structure with average grain size of about 56 μm was obtained after solution treatment at 800°C for 15 min followed by air cooling. Solution treated specimens were aged up to 800 h in the temperature range between 350 and 600°C. The morphology of the precipitates was varied significantly, depending on the aging temperature. The fine aggregates of α precipitates were dominant above 450°C. Peak hardness values were maintained up to 800 h at 500°C, which showed the superior thermal stability of α precipitates. Tensile strength increased up to 1600 MPa along with the decrease of elongation after aging at 350 and 400°C.     

Hot pressing of α-sialon powder prepared by SHS method

α-Sialon powder was made from α-Si₃N₄, Si, Y₂O₃ and AIN powders by a SHS process under 3 MPa nitrogen pressure. Hot pressing of the α-Sialon powder with added 0–8 wt.% YAG (Y₃Al₅O₁₂) at 2223 K for 1.5 hr under 30 MPa resulted in α/β-Sialon composites. α-Sialon content of the hot pressed sample was decreased as YAG content was increased. The number of elongated α- and β-Sialon grains was increased as the YAG content was increased. Vickers hardness of the hot pressed α/β-Sialon composites was decreased as the YAG content was increased, while both the fracture toughness and the flexural strength reached their maxima at 2 wt.% YAG addition.     

Oxidized implants and their influence on the bone response

Surface oxide properties are regarded to be of great importance in establishing successful osseointegration of titanium implants. Despite a large number of theoretical questions on the precise role of oxide properties of titanium implants, current knowledge obtained from in vivo studies is lacking. The present study is designed to address two aspects. The first is to verify whether oxide properties of titanium implants indeed influence the in vivo bone tissue responses. The second, is to investigate what oxide properties underline such bone tissue responses. For these purposes, screw-shaped/turned implants have been prepared by electrochemical oxidation methods, resulting in a wide range of oxide properties in terms of: (i) oxide thickness ranging from 200 to 1000 nm, (ii) the surface morphology of barrier and porous oxide film structures, (iii) micro pore configuration - pore sizes<8 microm by length, about 1.27 microm2 to 2.1 microm2 by area and porosity of about 12.7-24.4%, (iv) the crystal structures of amorphous, anatase and mixtures of anatase and rutile type, (v) the chemical compositions of TiO2 and finally, (vi) surface roughness of 0.96-1.03 microm (Sa). These implant oxide properties were divided into test implant samples of Group II, III, IV and V. Control samples (Group I) were turned commercially pure titanium implants. Quantitative bone tissue responses were evaluated biomechanically by resonance frequency analysis (RFA) and removal torque (RT) test. Quantitative histomorphometric analyses and qualitative enzyme histochemical detection of alkaline (ALP) and acidic phosphatase (ACP) activities were investigated on cut and ground sections after six weeks of implant insertion in rabbit tibia. In essence, from the biomechanical and quantitative histomorphometric measurements we concluded that oxide properties of titanium implants, i.e. the oxide thickness, the microporous structure, and the crystallinity significantly influence the bone tissue response. At this stage, however, it is not clear whether oxide properties influence the bone tissue response separately or synergistically.