Materials Science Forum Vols. 475-479

Abstract: The precipitation of copper in the non-oriental electrical steel was studied in this article. These precipitation particles, which influenced both the texture development and the magnetic properties of the steel sheets, appeared in the hot-rolling strips and grew up in the later normalization process. Their composition, morphology and crystallography had been investigated using TEM. Differed from the MnS and AlN that studied in the previous papers, these precipitate particles were found to be CuAl2. It suggested that these particles might stimulate the recrystallization nucleation of the {110} oriented grains and restrain the development of {111} oriented grains in the sheet of non-oriented electrical steel. This might be another explanation to the improvement on magnetic properties of the non-oriental electrical steel containing copper addition.

Abstract: High quality Fe3O4 thin film was synthesized by the magnetron sputtering method using Ar-H2 gas. Giant magneto resistance of the trilayer using Fe3O4 was investigated, where the observed MR ratio was less than 1%. A phenomenological calculation was made to make the origin of the small MR ratio clear, using a parallel current model assuming five passes. It is concluded that the non-magnetic layer surrounded by two magnetic layers is necessary to have the same order resistivity and similar thickness with Fe3O4 layer in order to obtain the large MR ratio for the trilayer using Fe3O4.

Abstract: In this study, in order to fabricate dental and medical bone plates, the effects of hydroxyapatite(HA) coating made of tooth ash and TiN coating prepared by electron-beam physical vapor deposition(EB-PVD) method on corrosion resistance and surface phenomena of Ti alloyed bone plates were investigated using various test methods. The coatings were deposited on the Ti-6Al-4V alloy fabricated by using a vacuum induction furnace. The corrosion behaviors of the samples were examined through potentiodynamic method in 0.9% NaCl solutions at 36.5±1°C and corrosion surface was observed using SEM and XPS. The surface roughness of TiN coated bone plates was lower than that of HA coated plates. The structure of TiN and HA coated layers showed the columnar structure. The corrosion potential was observed to be higher on the TiN and HA coated specimens than that of the non-coated alloy. The active current density was drastically lowered by both of TiN and HA coatings. The pit number and pit size of TiN and HA coated alloy were smaller in comparison with those of non-coated alloy. From the experimental results, it is suggested that TiN coated Ti alloy sample with rough surface has good protective propertiy against corrosion as well as HA coated bone plate alloy.

Abstract: New titanium alloys with a low elastic modulus have been developed for biomedical applications to avoid the stress shielding effect of an artificial prosthesis. The newly developed alloys contained the transition elements like Zr, Hf, Nb, Ta which were non-cytotoxicity elements and β stabilizers. In the present paper the elastic moduli of Ti-xM containing Zr, Hf, Nb, Ta were evaluated by measuring the velocity of supersonic wave (Pulse Echo Overlap). The effectiveness of the alloying elements for lowering the elastic modulus was investigated. In addition, the dominant factors for the low modulus were discussed. Ta was the most effective in lowering the elastic modulus of the alloys. The effectiveness of Hf was not acceptable for decreasing the elastic modulus. The dominant factor was the lattice parameter for Zr, and the poisson's ratio for Nb, Ta, respectively, in lowering the elastic modulus of Ti.

Abstract: Super stainless steel has been used to solve corrosion problems of biomaterials because it shows the excellent corrosion resistance as like Ti and Ti alloys and has better mechanical properties than Ti and Ti alloys. We designed high Mo and Ni bearing super austenitic stainless steel. To obtain desirable microstructure, Cr, Ni, Mo, N contents were controlled. This work focused on the role of alloying elements on cytotoxic behavior and corrosion of stainless steel. In acidic chloride solution, when the alloys had high PRE values, the alloys showed high pitting resistance and low critical current density. However, in Hanks’ solution, the higher PRE’s alloys showed high critical passive current density. Namely, it was revealed that EDTA among Hanks’ solution played an important role to increase the critical passive current density of high Mo and Ni bearing super stainless steels, regardless of PRE’s value of the alloys. Therefore, even if the PRE values of the alloys were higher, high Ni and Mo bearing alloys would reveal more cytotoxic and high metal ion release rate than 316L stainless steel.

Abstract: The deformation characteristics of a beta-type Ti-29%Nb-13%Ta-5%Zr alloy, developed for biomedical application, and their relation with the microstructure are investigated. The cold-rolled specimen is subjected to a tensile test at high temperatures ranging from 700 to 800°C under a constant cross-head speed ranging from 1×10-4 to 1×10-2s-1. The elongations tested at different temperatures are compared with that of Ti-15%V-3%Cr-3%Sn-3%Al, a typical beta titanium alloy. The deformation mechanism is characterized from the parameter of the strain rate sensitivity. The microstructures before and after the tensile test are observed with optical microscope and the correspondent grain sizes are measured. The grain growth during the deformation is also described.

Abstract: Duplex calcia coating method where firstly fine calcia was coated on wax pattern and then fine calcia reinforced silica fiber was coated on the fine calcia coated wax pattern, that is, duplex calcia coating method, was applied for making mold. The surface of Ti-29Nb-13Ta-4.6Zr cast using the duplex calcia coating method show very fine metallic lust. The thickness of alpha case formed on the surface of Ti-29Nb-13Ta-4.6Zr is much thinner comparing with the case where the commercial magnesia mold for casting conventional titanium and its alloys for dental applications is used. The duplex calcia coating method is highly expected to be put into practical use for dental precision casting of Ti-29Nb-13Ta-4.6Zr. The dental crown of Ti-29Nb-13Ta-4.6Zr is successfully fabricated using duplex calcia coating method.

Abstract: In the present study, the effects of Ta content on the dynamic Young’s modulus and tensile properties of Ti−Ta alloys were investigated in order to find a Ti−Ta alloy that gives low modulus and high strength for biomedical applications. For this purpose, the ingots of Ti−Ta alloys with Ta contents from 10 to 50 mass % were melted, and then rolled into the plate of 3 mm thick. All the specimens were solution treated at 1223 K in the b field for 3.6 ks and then quenched in ice water. Subsequently, some of them were aged at 773 K for 259.2 ks followed by a rapid quenching in ice water. The corrosion capacity and biocompatibility of typical Ti−Ta alloy were also evaluated. The experimental results indicate that the Ti−30% Ta alloy has better mechanical biocompatibility, corrosion capacity and cyto-toxicity than Ti−6Al−4V alloy used as a standard biomaterial, and thus it will be of considerable development for biomedical applications.

Abstract: Nitrogen-doped and -undoped Ti powders were obtained by Plasma Rotating Electrode Process (PREP) in an Ar atmosphere using Ar-2 vol.%N2 and pure Ar, respectively, for plasma flame. Auger electron spectroscopy (AES) revealed that nitrogen is enriched at the surface of nitrogen-doped Ti powder and decreases along with the depth direction. Microstructure of a compact prepared by hot pressing the nitrogen-doped Ti powder shows a shell structure. The outer area is considered to form by the diffusion of nitrogen. This microstructure disappears after annealing at 1373 K for 3.6 ks. It is found that the compressive yield strength of porous Ti compacts can be improved by introducing nitrogen in Ti powder and is superior to that of human cortical bone.