三浦 永理

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti–29Nb–13Ta–4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr– 0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3–3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb– 2Ta–3Zr–0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti–29Nb–13Ta–4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross‐sectional transmission electron microscopic observations of the microstructure of oxidized Ti–29Nb–13Ta–4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in‐ and outdiffusion occur during oxidation in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, whereas only out‐diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti‐36Nb‐2Ta‐3Zr‐0.3O are attributed to their dense microstructures composing of fine particles, and a composition‐graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti–Nb–Ta–Zr alloy is discussed.

One of the applications of titanium in the dental field is a porcelain-fired-metal crown. It is made by firing porcelain multiple times with different composition of ceramics on a metallic abutment tooth. Regarding firing process to metallic abutment, a primer is generally required to be applied in advance of a porcelain firing and the opaque porcelain is applied to cover the metallic color of the abutment. By the way, our recent research shows that white oxide films formed on the Ti substrate have a color tone similar to opaque porcelain. Therefore, porcelain-fired-Ti samples replacing primer and opaque porcelain firing with the TiO2 oxide layer were fabricated and evaluated in this study. Color tone and peel strength were evaluated, and cross-sectional observation was observed by SEM and EPMA.