Tadashi Asahina

Processing of biocompatible porous Ti and Mg

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Youngs modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Processing and mechanical properties of autogenous titanium implant materials.

Pure titanium and some of its alloys are currently considered as the most attractive metallic materials for biomedical applications due to their excellent mechanical properties, corrosion resistance, and biocompatibility. It has been demonstrated that titanium and titanium alloys are well accepted by human tissues as compared to other metals such as SUS316L stainless steel and Co–Cr–Mo type alloy. In the present study, highly porous titanium foams with porosities ≤80% are produced by using a novel powder metallurgical process, which includes the adding of the selected spacers into the starting powders. The optimal process parameters are investigated. The porous titanium foams are characterized by using optical microscopy and scanning electron microscopy. The distribution of the pore size is measured by quantitative image analyses. The mechanical properties are investigated by compressive tests. This open-cellular titanium foams, with the pore size of 200–500 μm are expected to be a very promising biomaterial candidates for bone implants because its porous structure permits the ingrowths of new-bone tissues and the transport of body fluids.

Microstructural evolution and superplasticity of rolled Mg-9Al-1Zn

Abstract Microstructural evolution and superplasticity of a Mg-9Al-1Zn alloy rolled at 673 K were investigated at 573 K and 1.5×10−3 s−1. The grain size of the as-rolled Mg alloy was 39.5 μm. However, the grain size of the specimen deformed to a true strain of 0.6 was 9.1 μm. The grain refinement was attributed to dynamically continuous recrystallization during an initial stage of tensile test. Stabilization of subgrain boundaries by fine particles and stimulation of continuous recrystallization by prior warm-deformation were not needed to attain dynamically continuous recrystallization in the Mg alloy. As a result of the grain refinement, the rolled Mg alloy exhibited superplastic behavior.

Processing of Cellular Magnesium Materials

Especially cellular aluminum materials have been extensively developed and investigated in the recent years. But also magnesium is a suitable metal for cellular metals due to its low density. By a special casting method open-cellular magnesium with a very loin density of 0.05 g/cm 3 is fabricated that shows high potential for usage as energy absorbers.

Deformation behavior and strengthening mechanisms at intermediate temperatures in W-La2O3

Abstract Tensile properties have been investigated at 1273–1973 K in rolled and annealed pure W and W-La 2 O 3 sheets. The as-rolled W-La 2 O 3 showed almost the same strength as the as-rolled pure W. On the other hand, the annealed W-La 2 O 3 exhibited higher strength than the annealed pure W. The higher strength of the annealed W-La 2 O 3 is attributed not only to the dislocation-particle interaction but also to the substructure which is stabilized by the La 2 O 3 particles.

Effects of heat treatment on compressive properties of AZ91 Mg and SG91A Al foams with open-cell structure

Compressive properties were investigated for the as-cast and T6 heat-treated AZ91 Mg and SG91A Al foams with open-cell structure. The foams showed an elastic region at an initial stage, then a plateau region with a nearly constant flow stress to a large strain of about 60%, and finally a densification region where the stress increased rapidly. The relative stress of the as-cast foams was higher than that of the T6 foams, taking into consideration the influence of the relative density.

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.

Tensile properties at elevated temperature of W-1%La2O3

The tensile properties were investigated from 1273 to 1973 K for recrystallized pure W and W-1%La2O3. The WLa2O3 showed much higher strength than the pure W, but slightly lower elongation, except at 1273 K where the pure W suffered from intergranular fracture. The excellent mechanical properties of the WLa2O3 are probably the result of the structure, consisting of elongated grains, which resists grain boundary sliding.

Compressive properties of open-cellular SG91A Al and AZ91 Mg

Abstract Mechanical properties of open-cellular SG91A Al and AZ91 Mg have been investigated by compressive tests. The strain to densification of the cellular AZ91 Mg was almost the same as that of the cellular SG91A Al, though the AZ91 Mg solid with the relative density of 100% showed much lower ductility than the SG91A Al solid. By compensation with the yield stress of the solid and the relative density, the stress–strain relation of the cellular AZ91 Mg was in agreement with that of the cellular SG91A Al.

Compressive deformation behavior of Al2O3 foam

Deformation behavior of an Al2O3 foam with an open-cellular structure was investigated by compressive tests. The variation in flow stress with strain was significantly large and there was no densification region. Breakage of the columns is responsible for the large variation in flow stress with strain and no densification region. The relative stress of the Al2O3 foam was lower than the value predicted by Gibson and Ashby. This is probably because of the high degree of cracking in the columns and the presence of partial closed-faces.