Yasumasa Chino

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.

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.

Superplasticity and grain boundary sliding in rolled AZ91 magnesium alloy at high strain rates

Abstract The superplastic deformation characteristics and microstructure evolution of the rolled AZ91 magnesium alloys at temperatures ranging from 623 to 698 K (0.67–0.76 Tm) and at the high strain rates ranging from 10−3 to 1 s−1 were investigated with the methods of OM, SEM and TEM. An excellent superplasticity with the maximum elongation to failure of 455% was obtained at 623 K and the strain rate of 10−3 s−1 in the rolled AZ91 magnesium alloys and its strain rate sensitivity m is high, up to 0.64. The dominant deformation mechanism in high strain rate superplasticity is still grain boundary sliding (GBS), which was studied systematically in this study. The dislocation creep controlled by grain boundary diffusion was considered the main accommodation mechanism, which was observed in this study.

An investigation of compressive deformation behaviour for AZ91 Mg alloy containing a small volume of liquid

Deformation behavior and formability of AZ91 magnesium alloy containing a small volume of liquid were investigated by compressive tests between 703 and 803 K and by forging tests between 753 and 803 K. Partial melting occurred initially at 743 K, however, the deformation mechanism changed at 773 K. Thus, the presence of liquid does not always lead to a change in deformation mechanism. The forging tests showed that excellent formability was attained at more than 773 K. It was suggested that the liquid serves to relax the stress concentrations caused by piles of dislocations, resulting in acceleration in flow of the solid. Also, grain refinement due to dynamic recrystallization was attained. Thus, both excellent formability and grain refinement were simultaneously attained by compressive deformation in a semi-solid state containing a small volume of liquid.

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.

Influences of grain size on mechanical properties of extruded AZ91 Mg alloy after different extrusion processes

The development of a plastic forming process is essential for the manufacture of magnesium products for automobile and aerospace applications. In this communication, influences of grain size on mechanical properties in the extruded Mg alloys after the normal extrusion and the ECA extrusion process are investigated.

Fabrication of Mg alloy tubes for biodegradable stent application.

Though Mg alloys are promising candidates for biodegradable stents, it is very difficult to fabricate stent tubes with high dimensional accuracy using Mg alloys because of their low deformability. This study aimed to develop thin-walled, high-quality Mg alloy tubes with good performance in stent applications. Cold drawing with a fixed mandrel was carried out for extruded Mg-0.8%Ca and AZ61 alloy tubes using optimized drawing parameters and lubrication, and stent tubes with 1.5-1.8mm outer diameter and 150 μm thickness were fabricated. A dimensional evaluation showed that the tube dimensional errors were within 0.02-2.5%. Also, an immersion test of pure Mg with different crystal orientations showed that the crystal orientation affected the corrosion properties, results that are the same with other Mg alloys. The crystal orientation of the stent tube could be controlled by changing the deformation amount and direction in the drawing, showing that it is possible to further improve the biodegradability of stents by approaching their fabrication from a processing aspect.

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.