Substrate Temperature Dependent Properties of Sputtered AlN:Er Thin Film for In-Situ Luminescence Sensing of Al/AlN Multilayer Coating Health.

The integrity and reliability of surface protective coatings deposited on metal surface could be in-situ monitored via the attractive luminescence sensing technique. In this paper, we report the influence of substrate temperature on the properties of erbium (Er) doped aluminum nitride (AlN) film, which could be applied as a luminescent layer for monitoring the health of multilayered Al/AlN coating. The AlN:Er films were deposited via reactive radio-frequency magnetron sputtering, and the silicon substrate temperature was varied from non-intentional heating up to 400 °C. The composition, morphology, crystalline structure, and dielectric function of the AlN:Er films deposited under these different substrate temperature conditions were studied. These properties of the AlN:Er films show strong correlation with the substrate temperature maintained during film fabrication. The obtained AlN:Er films, without further annealing, exhibited photoluminescence peaks of the Er3+ ions in the visible wavelength range and the strongest photoluminescence intensity was observed for the AlN:Er film deposited with the temperature of substrate kept at 300 °C. The results demonstrated in this work offer guidance to optimize the substrate temperature for the deposition of AlN:Er film for future application of this sensing technique to thin metal components.

Fretting Wear Behavior and Photoelectron Spectroscopy (XPS) Analysis of a Ti/TiN Multilayer Film Deposited on Depleted Uranium.

Depleted uranium has been widely applied in nuclear energy fields. However, its poor corrosion and wear resistance restrict its applications. A titanium/titanium nitride (Ti/TiN) multilayer film was deposited on a uranium surface to improve its fretting wear resistance. Fretting wear tests were carried out using a pin-on-disc configuration. The fretting behaviors of uranium and the Ti/TiN film were investigated under different normal loads. With the normal load increasing, the mode of fretting wear gradually transformed from slip region (SR) to mixed fretting region (MFR) and then to partial slip region (PSR). It is illustrated that the normal load had an obvious effect on the fretting wear behavior. The friction coefficients of both uranium and Ti/TiN multilayer film decreased with the increase of the normal load. In SR, the main wear mechanisms were delamination and abrasion for uncoated uranium, and delamination and oxidation for uranium coated with the Ti/TiN multilayer film. Photoelectron spectroscopy (XPS) analysis also showed that the Ti/TiN coating was oxidized and formed TiO2 during fretting wear. The wear depth of naked uranium was much greater than that of coated uranium, which demonstrated that the Ti/TiN multilayer film could effectively improve the wear properties of uranium.

Effect of frequency on fretting wear behavior of Ti/TiN multilayer film on depleted uranium.

The Ti/TiN multi-layer film was prepared on the depleted uranium (DU) substrate by cathodic arc ion plating equipment. The character of multi-layer film was studied by SEM, XRD and AES, revealed that the surface was composed of small compact particle and the cross-section had a multi-layer structure. The fretting wear performance under different frequencies was performed by a MFT-6000 machine with a ball-on-plate configuration. The wear morphology was analyzed by white light interferometer, OM and SEM with an EDX. The result shows the Ti/TiN multi-layer film could greatly improve the fretting wear performance compared to the DU substrate. The fretting wear running and damaged behavior are strongly dependent on the film and test frequency. The fretting region of DU substrate and Ti/TiN multi-layer under low test frequency is gross slip. With the increase of test frequency, the fretting region of Ti/TiN multi-layer change from gross slip to mixed fretting, then to partial slip.

Interface structure and corrosion resistance of Ti/Cr nanomultilayer film prepared by magnetron sputtering on depleted uranium.

Uranium has broadened utility in military and civilization; however, it is extremely apt to oxidation corrosion. Ti/Cr nanomultilayer film was prepared by unbalanced magnetron sputtering on the surface of depleted uranium (DU) to improve its corrosion resistance. The SEM morphologies show that Ti/Cr multilayer film has fine grain and high density. The Auger electron spectroscopy is used to investigate the depth profiles of Ti, U, and O elements of interface between DU substrate and the Ti interlayer, and indicates that the mutual diffusion area of U and Ti is formed at the interface. The TEM cross-section microstructure shows that the multilayer film has alternative Ti and Cr layers and form a perfect modulation structure. The modulation period is measured to be 4.8 nm in TEM morphology, the thickness ratio of Ti to Cr could be estimated to be about 1:2. Potentiodynamic polarization curves show that, after depositing Ti/Cr nanomultilayer film, the corrosion potential increases while the corrosion current density decreases obviously. The surface of Ti/Cr nanomultilayer film exhibits a pseudo passivation behavior when the polarization potential increased from -50 to 400 mV. It was indicated that, after depositing Ti/Cr nanomultilayer film by unbalanced magnetron sputtering, the corrosion resistance of DU was effectively improved.

[The corrosion of pure iron in five different mediums].

The sectional test was adopted in this study to investigate the corrosion of pure iron in 0.15 mol/L NaCl solution, Ringer solution, PBS(-) solution, SBF solution and M199 cell culture medium at three different times. The result shows that different mediums have different corrosion effects on pure iron. The arrangement according to the medium's corrosion ability from the strongest to weakest is 0.15 mol/L NaCl solution (Ringer solution), PBS(-) solution, SBF solution and M199 cell culture medium. The results of scanning electron microscopy and energy dispersive X-ray spectrum analyses show that the addition of HPO4(2-), H2POC4-, Ca2+, Mg2+, SO4(2-) and the organic component can inhibit the corrosion to some degree.

[Development of biodegradable magnesium-based biomaterials].

Magnesium is a macroelement which is indispensable to human bodies. As a lightweight metal with high specific strength and favorable biocompatibility, magnesium and its alloys have been introduced in the field of biomedical materials research and have a broad application prospect. It is possible to develop new type of biodegradable medical magnesium alloys by use of the poor corrosion resistance of magnesium. Bioabsorbable magnesium stents implanted in vivo could mechanically support the vessel in a short term, effectly prevent the acute coronary occlusion and in-stent restenosis, and then be gradully biodegraded and completely absorbed in a long term. Osteoconductive bioactivity in magnesium-based alloys could promote the apposition growth of bone tissue. This paper reviews the progress of magnesium and its alloys applied in bone tissue and cardiovascular stents, and the prospect of the future research of magnesium-based biomaterials is discussed.