Hiroyuki Hosokawa

Compressibility of porous magnesium foam: dependency on porosity and pore size

Mechanical properties of porous magnesium with the porosity of 35–55% and the pore size of about 70–400 μm are investigated by compressive tests focusing on the effects of the porosity and pore size on the Youngs modulus and strength. Results indicated that the Youngs modulus and peak stress increase with decreasing porosity and pore size. The mechanical properties of the porous magnesium were in a range of those of cancellous bone. Therefore, it is suggested that the porous magnesium is one of promising scaffold materials for hard tissue regeneration.

Novel titanium foam for bone tissue engineering

Titanium foams fabricated by a new powder metallurgical process have bimodal pore distribution architecture (i.e., macropores and micropores), mimicking natural bone. The mechanical properties of the titanium foam with low relative densities of approximately 0.20-0.30 are close to those of human cancellous bone. Also, mechanical properties of the titanium foams with high relative densities of approximately 0.50-0.65 are close to those of human cortical bone. Furthermore, titanium foams exhibit good ability to form a bonelike apatite layer throughout the foams after pretreatment with a simple thermochemical process and then immersion in a simulated body fluid. The present study illustrates the feasibility of using the titanium foams as implant materials in bone tissue engineering applications, highlighting their excellent biomechanical properties and bioactivity.

Diffusion bonding in superplastic magnesium alloys

The superplastic characteristic and diffusion bonding behavior were investigated in a commercial AZ31 magnesium alloy sheet having equiaxed grain size with an average size of 16.8 μm. The alloy behaved in a superplastic manner from 623 to 723 K, and, the present material was successfully diffusion bonded at the superplastic temperature by selecting appropriate pressure and time. The maximum of lap shear strength was 0.85 at a bonding pressure of 3 MPa and a bonding temperature of 673 K, with a bonding time of 3 h. In the specimen with high ratio of lap shear strength, the bond line was not identified by optical microscopy.

Processing of fine-grained aluminum foam by spark plasma sintering

Porous materials are now becoming attractive to researchers interested in both scientific and industrial applications due to their unique combinations of physical, mechanical, thermal, electrical and acoustic properties in conjunction with excellent energy absorption characteristics. Metallic foams allow efficient conversion of impact energy into deformation work, which has led to increasing applications in energy absorption devices. In particular, foams made of aluminum and its alloys are of special interest because they can be used as lightweight panels, for energy absorption in crash situations and sound or heat absorbing functions in the automotive industry with the aim to reduce weight to improve crashworthiness, safety and comfort.

Quantitative assessment of superplastic deformation behavior in a commercial 5083 alloy

Abstract This paper describes the constitutive equation for the superplastic commercial 5083 (Al–Mg–Mn–Cr) alloy effective in a temperature range of 773–843 K and at a strain-rate range from 10−5 to 4×10−3 s−1. The superplastic properties have been investigated using velocity jump tests. The analysis of the experimental results reveals that the true stress exponent is two, and the true activation energy for superplastic flow is similar to the lattice self-diffusion of aluminum (142 kJ mol−1). All mechanical data can be represented by a single constitutive equation for superplasticity according to the Dorn equation.

Fabrication of nanoscale Ti honeycombs by focused ion beam

Ti honeycombs with the side of 800 and 400 nm were fabricated by focused ion beam (FIB), though the surfaces of the bottom and wall of the Ti honeycombs were rough, as compared with the surfaces of the bottom and wall of the Si honeycomb. It is demonstrated that the nanoscale Ti components can be fabricated in a short time by FIB.

Porous Bioresorbable Magnesium as Bone Substitute

Recently magnesium has been recognized as a very promising biomaterial for bone substitutes because of its excellent properties of biocompatibility, biodegradability and bioresorbability. In the present study, magnesium foams were fabricated by using a powder metallurgical process. Scanning electron microscopy equipped with energy dispersive X~ray spectrometer (EDS) and compressive tester were used to characterize the porous magnesium. Results show that the Youngs modulus and the peak stress of the porous magnesium increase with decreasing porosity and pore size. This study suggests that the mechanical properties of the porous magnesium with the low porosity of 35 % andlor with the small pore size of about 70 μ are close to those of human cancellous bones.

Materials design for industrial forming process in high-strain-rate superplastic Al-Si alloy

Abstract The optimum materials design in microstructural control could be developed for the high-strain-rate superplastic materials in the industrial scale. In the present work, it is reported that the high-performance-engine pistons with near-net-shape can be fabricated by the superplastic forging technology in the high-strain-rate superplastic PM Al-Si based alloy, which is produced by using this optimum materials design.

Influence of Cobalt Content on the Fatigue Strength of WC-Co Hardmetals

The behavior of hardmetals under cyclic loads is investigated. Unnotched specimens were employed to obtain practical information regarding fatigue in hardmetals. All the tested hardmetals exhibit an increase in the number of cycles until failure with a decrease in the maximum stress, i.e., the hardmetals exhibit a high fatigue sensitivity. The fatigue strength increases with the cobalt content. Although distinct fatigue limits, as observed in metals, cannot be observed, the calculated fatigue limit stress at 107 cycles is found to be approximately 70% of the flexural strength, and the stress value exhibits a linear relationship with the flexural stress.

Processing and Mechanical Properties of Open-Cell Mg Alloys

Mechanical properties of open-cellular magnesium alloys with three types of geometric cell-structures, that is, a random round cell-structure (type A). a controlled diamond cell-structure for which the angle between the struts and the load direction is 45 degree (type B) and a controlled square cell-structure for which the angle between the struts and the loading direction is 0 degree (90 degree) (type C), are investigated by compressive tests. Results indicate that type C showed a higher collapse stress than the other two types. The collapse mechanism and the effects of the loading direction on collapse stress for the three types of magnesium alloys arc discussed from the viewpoint of bending, buckling and yielding of the struts. It is suggested that collapse for the open-cellular magnesium aHoys is associated with yielding of struts