The purposes of this study were to evaluate the microstructures and chemical composition changes of the surface of tetragonal zirconia polycrystal (TZP) after irradiation of nanosecond pulsed laser and to consider the effects for biocompatibility. Two types of zirconia ceramics, yttria-stabilized TZP (Y-TZP) and ceria-stabilized TZP/alumina nanocomposite (Ce-TZP), were irradiated. To evaluate microstructures, the irradiated samples were observed with a scanning electron microscope (SEM). Laser irradiation blackened the surface of Ce-TZP; contrastingly, it gave no color change on that of Y-TZP. To identify the chemical composition changes, the samples were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). To examine the changes in the surface chargeability of zirconia, zeta potential was determined. SEM images showed microgrooves, whose widths were the same as that of laser spot (30 μm), were formed on the surfaces of both samples, and the surfaces of the grooves were roughened by coagulation materials of a few micrometers in size. Such cell-sized grooves with rough surfaces are considered a favorable environment to help osteoblast cells to grow. XRD patterns showed that laser irradiation induced monoclinic-to-tetragonal phase transform. Because the monoclinic phase was induced by machining or polishing, this result means laser irradiation returned the crystal phase to the bulk state. However, XRD patterns did not reveal the reason of the color change. EDX result showed oxygen atoms decreased on the irradiated surface of both samples. In addition, XPS spectra of Zr3d from Ce-TZP showed a part of Zr⁴⁺ shifted to lower side after irradiation. Considering these points, the color change was caused by the generation of oxygen-deficient zirconia. After laser irradiation, zeta potential of Ce-TZP was decreased. This result suggests the possibility that the amount of deposition of ions and proteins in body liquid is decreased. It is concluded that the grooves to improve biocompatibility can be formed on TZP surfaces by nanosecond pulsed laser, but adverse chemical composition change can be occurred by deficiency of oxygen. Additional process may be needed to prevent the phenomenon.

In this study, to obtain guidelines for inhibiting the combustion of the molten metal in magnesium alloys, AZ91D magnesium alloy and AZ91 magnesium alloy with added calcium were exposed to the atmosphere, and the surfaces of the alloys were observed. In the case of AZ91D magnesium alloy, aggregated products were observed on the surface of the molten alloy. In the case of AZ91 alloy with added calcium, aggregated products were not observed. A CaO layer was formed on the outermost surface of the molten alloy, and a MgO layer was formed below the CaO layer. With increasing exposure time, the thicknesses of these layers remained almost constant. It was considered that the CaO layer, in which aluminum did not appear, inhibited combustion by limiting the flow of magnesium vapor from the molten alloy to the atmosphere and the oxidation of magnesium over a long time.

Under pressurized water reactor primary conditions, the intergranular stress corrosion cracking susceptibility of Ni base alloy is improved by chromium carbide precipitation in the grain boundaries. The effects of chromium carbide precipitation treatments are explained by the grain boundary strengthening mechanism, the intergranular corrosion prevention mechanism, and so forth. However, few studies demonstratate these mechanisms, and the effects on intergranular stress corrosion cracking susceptibility are not completely understood. Therefore, for the purpose of demonstrating the internal stress distribution change with or without grain boundary carbide precipitation treatment in alloy 600, in-situ measurments using the X-ray diffraction technique at BL28B2 of SPring-8 applying tensil stress were carried out. The results confirmed that there is a difference in the strain distribution in grain boundaries and inner grains. Intergranular stress corrosion cracking is suppressed by preventing stress concentration in grain boundaries due to carbides precipitated at grain boundaries.

The effects of external stress on the nucleation of bar-like α-precipitates were examined for a Ti-20 mass％Mo alloy aged at 773 K. Overall, the application of a tensile stress accelerated the nucleation of α-precipitates, whereas a compressive stress did not significantly affect it. Specifically, the tensile stress promoted the formation of α-precipitates when the misfit strain ε_M of the precipitates along the loading direction was greater than 0; however, it did not significantly affect the precipitate nucleation in case where ε_M < 0. In contrast, the compressive stress promoted the precipitate nucleation when ε_M < 0 and did not significantly influence it when ε_M > 0. The average misfit strain of the α-precipitate was estimated as 0.019 from measurements of length change and lattice parameter of the β-Ti matrix.