Akira Nozue

Metal ions induce bone-resorbing cytokine production through the redox pathway in synoviocytes and bone marrow macrophages.

To evaluate the biological reactions to metal ions potentially released from prosthetic implants, we examined the ability of metal ions to produce bone-resorbing cytokines and the underlying mechanism using synoviocytes and bone marrow (BM) macrophages. The cells were incubated with NiCl(2), CoCl(2), CrCl(3) or Fe(2)(SO(4))(3) at optimal concentrations, which are detectable in joint fluid following total joint arthroplasty. The production of interleukin-1beta, interleukin-6 and tumor necrosis factor-alpha were enhanced by all metal ions tested as determined by enzyme-linked immunosorbent assay. From the results of electrophoresis mobility shift assay, all metal ions enhanced the DNA-binding activity of nuclear factor kappaB (NF-kappaB), and p50-p65 heterodimers and p50 homodimers were the major subunits. These effects of the metal ions were considerably blocked by pyrrolidine dithiocarbamate (PDTC) known as a radical scavenger. An electron spin resonance study clearly demonstrated the ability of metal ions to generate activated oxygen species (AOS), especially hydroxyl radicals (*OH), which accounts for PDTC-blockade of metal ion-induced NF-kappaB activation and subsequent cytokine production. Taken together, our data raised the possibility that small amounts of metal ions released from prosthetic implants activate synoviocytes and BM macrophages through the AOS-mediated process (i.e. the redox pathway), and contribute to the initiation of osteolysis at the bone-implant interface.

Mechanical and thermal properties of silicon-carbide composites fabricated with short Tyranno® Si-Zr-C-O fibre

Silicon carbide (SiC) composites reinforced with 10–50 mass% (10.5–51.2 vol%) of short Tyranno® Si-Zr-C-O fibre (average length ∼0.5 mm) and 0–10 mol% of Al4C3as a sintering aid were fabricated using the hot-pressing technique. Firstly, the effect of Si-Zr-C-O fibre addition on the relative density (bulk density/true density) of the SiC composite hot-pressed at 1800 °C for 30 min was examined by fixing the amount of Al4C3to be 5 mol%. Although the relative density was reduced to 87.4% for 10 mass% of Si-Zr-C-O addition, further increases in the amount of Si-Zr-C-O fibre increased density to a maximum of 92.8% at 40 mass% of fibre addition. Secondly, the effect of varying the amount of Al4C3addition on the relative density was examined by fixing the amount of Si-Zr-C-O fibre to be 40 mass%. The optimum amount of Al4C3addition for the fabrication of dense SiC composite was found to be 5 mol%. The fracture toughness of the hot-pressed SiC composites with 20–40 mass% of Si-Zr-C-O fibre addition (amount of Al4C3: 5 mol%) was 3.2–3.4 MPa · m1/2and approximately 1.5 times higher than that (2.39 MPa · m1/2) of the hot-pressed SiC composite with no Si-Zr-C-O fibre addition. SEM observation showed evidence of Si-Zr-C-O fibre debonding and pull-out at the fracture surfaces. The hot-pressed SiC composite with 5 mol% of Al4C3and 40 mass% of Si-Zr-C-O fibre additions showed excellent heat-resistance at 1300 °C in air due to the formation of a SiO2layer at and near exposed surfaces.

Densification and microstructural developments during the sintering of aluminium silicon carbide

Densification and microstructural developments during the sintering of aluminum silicon carbide (Al4SiC4) were examined. Two types of Al4SiC4 powders were prepared by the solid-state reactions between: (i) Al, Si, and C at 1600°C for 10 h (designated as Al4SiC4(SSR)), and (ii) chemically-vapour deposited ultrafine Al4C3 and SiC powders at 1500°C for 4 h (Al4SiC4(CVD/SSR)). The specific surface areas of the Al4SiC4(SSR) and Al4SiC4(CVD/SSR) powders were 2.7 and 15.5 m2 · g−1, respectively. Relative densities of the pressureless-sintered Al4SiC4(SSR) and Al4SiC4(CVD/SSR) compacts were as low as 60–70% for firing temperatures between 1700°C and 2000°C. The relative densities of Al4SiC4(SSR) and Al4SiC4(CVD/SSR) compacts could be enhanced using the hot-pressing technique; the relative density of the Al4SiC4(SSR) compact hot-pressed at 1900°C for 3 h was 97.0% whereas that of the Al4SiC4(CVD/SSR) compact hot-pressed at 1900°C for 1 h attained 99.0%. The former microstructure was composed of plate-like grains of width 10–30 μm and thickness ∼10 μm whilst the latter microstructure was comprised of equiaxed grains with a typical diameter of ∼10 μm. Densification of the Al4SiC4(CVD/SSR) compacts appeared to be promoted compared to the Al4SiC4(SSR) compact and this was attributed to the higher surface area, reduced agglomeration of the starting primary particles, and more homogeneous chemical composition.

A probabilistic approach to the toughening mechanism in short-fiber-reinforced ceramic-matrix composites

The toughening mechanism in brittle ceramic-matrix composites reinforced with short fibers is analytically studied by considering probabilistic aspects of fiber strength. Energy for broken and/or unbroken fibers to be pulled out is given on the assumption that the resistant force at the fiber interface is uniform along the sliding area. The effect of fiber inclination is incorporated by the introduction of a resistant force proportional to the normal component of the bridging force on the fiber and a stress magnification factor. This considers significant local deformation of the fiber near the crack surface. Fiber breakage is assumed to occur at the randomly distributed flaws whose expected number in a unit length follows a power law of the stress. This assumption is consistent with the fact that the strength of a fibre of a certain length is expressed by a Weibull distribution function. The energy dissipated as a result of fiber pull-out for a unit area of major crack propagation is estimated for continuous unidirectional composites, aligned short-fiber composites and two- and three-dimensional random short-fiber composites.

Microstructure and environment-dependent fatigue crack propagation properties of Ti-48Al intermetallics

Fatigue crack propagation properties of Ti-48Al were studied by means of in-situ observation of the crack growth process under vacuum and air conditions. Three types of microstructures, namely, as-cast, duplex and fully lamellar structure were investigated in the present study. The results show that the crack growth behavior is dependent on the microstructure and the angle between the crack growth direction and orientation of lamellar colonies. The preferred path of crack propagation through the weakest phase of the structure associated with microcracking within the crack tip plastic zone has been investigated. The accelerated crack growth observed in air environment is attributed to absorption of air humidity at the crack tip plastic zone. This phenomenon is apparent through the observation of crack propagation process and the resulting fractured surface.

Fracture behaviour of boride-dispersed composites fabricated by hot-pressing amorphous Ni60Mo30B10 powder

Microstructural and mechanical property characteristics were investigated for three boride-dispersed composites fabricated by hot-pressing amorphous Ni60Mo30B10 powder. The first composite was tested in the as-hot-pressed condition (HP) whilst the other specimens were subjected to a solution treatment (ST) and further ageing (STA). X-ray diffraction showed the HP and ST composites to consist of Mo2NiB2 particles in a Ni-rich matrix whilst the STA material contained Mo2NiB2 particles in a NiB3Mo matrix. The hardness and fracture toughness decreased and increased, respectively, for the ST material compared to the HP case whilst the STA case showed increased and decreased hardness and fracture toughness, respectively, compared to the ST composite. These results were explained in terms of the brittle–ductile–brittle fracture modes for the HP–ST–STA specimens. In addition, the HP specimen showed only a 15% decrease in compressive strength at 973 K compared to 303 K.

Biocompatibility of hydroxyapatite films formed on Ti metal by a simple urea and urease treatment

HAp films with good adhesive property were formed by a simple sur face treatment utilizing an enzyme reaction of urea with urease. The resulting coating layer consisted of carbonate-containing HAp with poor crystallinity. The in vitro evaluation using osteoblastic cells showed that HAp-coated Ti substrate had a good cellular response, such a s cell proliferation and differentiation into osteoblast. From the results of in vivo evaluation using rabbit models, the HAp-coated Ti substrate directly bonded to bones to form large amount of new bone around implant. It has been found from both the in vitro and in vivo evaluations that the present HAp-coated Ti substrate has excellent biocompatibility.

THE INTEGRITY EVALUATION OF THE WELD JOINT OF SPHERICAL ROCKET MOTOR CASE

Abstract The Institute of Space and Astronautical Science (ISAS) is undertaking the launching of spacecraft for space observations and interplanetary explorations. The spherical rocket motor case of satellite launchers was made of Ti-6A1-4V alloy, however, to reduce the weight and fabrication cost, the material of the case was changed to Ti-15V-3Cr-3Sn-3AI alloy because of its good cold formability and the high strength. However, it was found that the hardness of weld joint was higher than that of base metal and the fracture toughness was lower when heat treated by a conventional aging process. This report describes the development of a new heat treatment process to obtain the high strength of base metal and the high fracture toughness of the weld joint, and the evaluation of the integrity of the weld joint by acoustic emission and radiography. The developed heat treatment process is as follows: after solution treatment, the motor case was aged at a relatively low temperature (preaging), welded, and then ...

Some properties of silicon carbide composites fabricated with chopped Si-Al-C fibres

Silicon carbide (SiC) ceramics reinforced with 10∼50 mass% of chopped Si-Al-C fibre (average length; 394µm) and 5 mol% of A14C3 as a sintering aid were fabricated by hot pressing at 1800°C for 30 min under a pressure of 31 MPa. The hot-pressed SiC compact with 40 mass% of chopped Si-Al-C fibre addition showed a maximum relative density (96.8%) among the specimens examined and a Vickers hardness (Hv) of 28.3 GPa. The highest fracture toughness (KIC) (3.9 MPa • m1/2) was achieved at 30 mass% of Si-Al-C fibre addition. These Hv and KIC values were higher than those (Hv ;17.0 GPa and KIC 2.1 MPa • m1/2

Fatigue Crack Growth Mechanisms Of Cast Ti-48Al (at.%) Alloy

Substantial cost reduction for cast TiAl automotive parts could be achieved by eliminating hot isostatic pressing (HIPing) procedure during the material processing. In this respect, a cast Ti-48Al (at %) intermetallic alloy is evaluated in the non-HIPed condition with the objective to establish the fatigue crack growth response and identify the fracture mechanisms. For this purpose, a series of fatigue crack growth tests were performed on the alloy with three different microstructures, with a load ratio, R=0.1, in both air and vacuum environment. Environment effect is manifested in the threshold I”K levels of 9.6 and 13 MPaâˆsm for crack growth response in air and vacuum, respectively. In the intermediate range of crack growth rates between 10 -5 to 10-3 mm/cycle, crack bridging by shear ligament formation describes the crack growth process, with I”K varying from 13 to 35 MPaâˆsm. Extensive crack bridging effect in the duplex microstructure is reflected in the crack growth retardation which reaches the lowest minimum crack growth rate at 2A—10-6 mm/cycle in each of the three crack bridging stages observed. Other fatigue damage mechanisms observed are crack deflection, crack branching, stepped crack growth and microcracks initiation in the crack tip plastic zone, particularly at near threshold crack growth.