Papers by Author: Shuji Hanada

Abstract: . Low Young’s modulus is attained by controlling phase stability of  (bcc) Ti-Nb-Sn alloys consisting of non-cytotoxic elements, based on experimental results that Young’s modulus decreases with decreasing temperature toward ” (orthorhombic) martensitic transformation start temperature (Ms). Cold groove rolled, metastable  (Ti-35%Nb)-4%Sn alloy exhibits low Young’s modulus of about 40 GPa at 297 K, measured by the free resonance vibration method. This value is much lower than that of Ti-6%Al-4%V and close to that of human cortical bone. By heating one edge of the groove rolled rod to 573 K for 4 h, hardness and Young’s modulus are found to increase significantly at the heated zone and to change depending on distance from the heated zone. The increase in hardness is explained mainly by fine  precipitation and additionally by microstructure refinement through reverse transformation ”→ of deformation-induced martensite. From these results, an advanced stem having high strength at the necked part can be developed for a new artificial hip joint, keeping low Young’s modulus at the distal part implanted in a femur.

Abstract: A new fabrication process of a stem for an artificial hip joint has been investigated to improve mechanical properties and to reduce both the fabrication cost and consumption of expensive Ti alloys by swaging and die-forging into near-net-shape at room temperature, followed by local heat treatment and precise machining. In this study metastable Ti-Nb-Sn alloys consisting of non-cytotoxic elements (biocompatible Ti alloys) were used for biomedical applications. It is found that swaging at both ends of a rod before die-forging saves material consumption by approximately 50% in comparison with turning, and enhances subsequent age-hardening. In addition the cold die-forging enables the fabrication costs to decrease. It is suggested that high strength of higher than 1100 MPa in the proximal part connected to a stem head and low Young’s modulus of less than 60 GPa in the distal part implanted in a femur can be obtained simultaneously in advanced Ti alloy stems.

Abstract: The corrosion behavior of pre-treated Fe–Al alloy in a sulfuric acid solution and chloride-containing solution was studied. Alumina layer formed at 1073–1173 K on the surface of Fe–Al alloy improves the corrosion resistance of the alloy, whereas that at 1273 K does not improve it. This was explained by the defects of Al2O3 layer, the fraction of Al2O3 in the oxides, crystallity of Al2O3, and residual stress in the oxide layer. On the other hand, TiO2 layer produced by dip coating and subsequent annealing at 523–773 K slightly improved the corrosion resistance of the alloy. The effect of the oxide layer on the aqueous corrosion was discussed focusing on the quality of the oxide.

Abstract: Isothermal oxidation behavior of Al added Mo-Si-B in-situ composites was investigated under Ar-20%O2 and air atmosphere over the temperature range of 1073–1673 K. The Al added Mo-Si-B composites ((Mo-8.7mol%Si-17.4mol%B)-1mol%Al) were prepared by arc-melting, and homogenized at 2073 K for 24 h in an Ar-flow atmosphere. The ternary Mo-Si-B in-situ composite exhibited a rapid mass loss at the initial oxidation stage and then the passive oxidation after the substrates were sealed with borosilicate glass in the temperature range of 1173–1473 K, whereas it exhibited a rapid mass gain around 1073 K. On the other hand, the Al addition significantly improved the oxidation resistance of Mo-Si-B in-situ composites at temperatures from 1073–1573 K. These excellent oxidation resistances are considered to be due to the rapid formation of a continuous, dense scale of Al-Si-O complex oxides.

Abstract: Porous Ti compacts reinforced by ultra-high molecular weight polyethylene (UHMWPE) were fabricated and their mechanical properties were evaluated. Ti powder atomized by plasma rotating electrode process (PREP) was sintered at temperatures ranging from 1473 K to 1673 K for 7.2 ks in a vacuum. The porous Ti compacts contain the porosity of about 40%, irrespective of the sintering temperature. Porous Ti/UHMWPE composites were successfully fabricated by compressing UHMWPE powder into the porous Ti compacts. The compacts exhibit open pore structure and enables the penetration of UHMWPE into pores in the compacts. Young’s modulus of the composites is higher than that of the porous Ti compacts. The increment in Young’s modulus is not simply explained by the rule of mixture because Young’s modulus of the UHMWPE is approximately 1.3 GPa. Three-point bending strength of the composites is improved, presumably due to the local stress relief by UHMWPE in the vicinity of neck in the composites.

Abstract: The laminated composite of Fe–Al alloy and CrMo steel was fabricated by clad rolling to provide additional properties to the steel such as corrosion resistance, strength, and light weight. Three layered composite consisting of alloy/steel/alloy was succesfully fabricated using the process condition to satisfy the criteria for simultaneous deformation of different materials. The fabricated composite could be cold rolled to 120 μm thickness (99.8 % reduction), and wound to a coil without damage. The corrosion resistance of the composite in a sulfuric acid solution was comparable to that of monolithic CrMo steel, and it depends on the aluminium content of the Fe–Al alloy. The aluminium content dependence of the corrosion behavior is explained by the corrosion potential (Ecorr) of the Fe–Al alloy derived from the polarization curves in the solution. In order to improve the corrosion resistance of the composite, pre-oxidation treatment was conducted to form Al2O3 layer to protect the substrate. Analyses by XPS and SIMS show that the Al2O3 oxide fraction increases with the oxidization temperature and Al content of the alloy. The pre-oxidation treatment improved the corrosion resistance of the composite in a sulfuric acid solution. It is concluded that the effect of oxidation on the corrosion resistance is due to the formation of Al2O3 oxide and the Al2O3 fraction in the oxides.

Abstract: The present study was designed to investigate whether porous titanium (Ti) having Young’s modulus similar to bone has osteoconductive characteristics in rat critical-sized calvarial bone defect. The effect of coating by octacalcium phosphate (OCP) was also examined. OCP is known as a precursor of initial mineral crystals of biological apatite in bones and teeth. Ti powder was prepared by plasma rotating electrode process in an Ar atmosphere. Then, porous Ti disks, 8 mm in diameter with 1 mm thick, were obtained using the particles ranging from 300 to 500 +m, by sintering at 1573 K without applied pressure. The disks had about 35 vol% in porosity and about 10 GPa in Young’s modulus which corresponds to that of human cortical bone. Newly formed bone was observed so as to fill the pore up at 12 weeks, confirming the ability to conduct the ingrowths of the bone tissue. Although in vitro study showed that proliferation of mouse bone marrow stromal ST-2 cells was inhibited on the dishes coated by OCP rather than the control dish, OCP coating on porous Ti seemed to stimulate the bone formation in vivo. Taken together, it seems likely that porous Ti having Young’s modulus similar to bone shows osteoconductive characteristics to conduct bone ingrowths. OCP could be a potential coating agent to assist bone regeneration on porous Ti.

Abstract: The composite steel of iron-aluminum alloy and high carbon steel was fabricated by clad rolling, which process conditions were determined by the flow stress ratio between the constituents. Flow stress ratio of iron-aluminum alloy to carbon steel exhibits near unity at temperatures ranging from 873K to 1273K. Composite steel consisting of alloy/steel/alloy is successfully fabricated with about 70 % reduction in thickness, which demonstrates distinctive bending deformability. Clad plate is further rolled at room temperature to 150 µm in thickness with 98.3 % in reduction, and it is capable of winding without damage. The composite has shown significantly better high temperature oxidation resistance and corrosion resistance in a sulfuric acid than carbon steel. The dependency of corrosion resistance upon aluminum content of iron-aluminum alloy in an oxidation atmosphere is positive, whereas that in a sulfuric acid is negative. These results provide a strategy for the fabrication of functional composite steel.

Abstract: Nb-base in-situ composites, which have the base composition of Nb-18Si-5Mo-5Hf, have been investigated in microstructure, hardness (Hv*), Young’s modulus (E), tensile properties and fracture behavior. The microstructures of all composites examined consist of NbSS matrix and Nb5Si3 secondary phases. No secondary phase such as Nb2C appeared. The crystal structure of Nb5Si3 is Mn5Si3-type when C replaces 2mol%-Nb, though typical structures of a (Cr5B3-type) and b (W5Si3-type) as in the base composition when W replaces. W addition is effective in increasing Hv* and E of both phases as expected. However, C alloying is somewhat beneficial only in Nb5Si3 with a noticeable negative effect in NbSS. Furthermore, the composite exhibits the highest strength at 1473 K, while the base composite exhibits the highest at room temperature. The fracture behavior is independent of the compositions and it is controlled by cleavage fractures of Nb5Si3, decohesion of NbSS/Nb5Si3 interface and ductile rupture of NbSS depending on the testing temperatures.