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Materials (Basel) ; 12(1)2019 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-30609842


Surface mechanical attrition treatment (SMAT) was performed on a reduced ferritic/martensitic (RAFM) steel to form a nanostructured (NS) layer on the surface of the sample. Both electron backscatter diffraction (EBSD) and TEM were used to investigate the microstructure evolution during SMAT. The experimental results showed that there were three different zones after SMAT: (i) The "ultrafine grain" (UFG) zone, observed at the top-most surface region, (ii) the "transition zone" in which the original grains were fragmented under the severe plastic deformation and (iii) the "deformed zone" in which the original grains were simply deformed. The average grain sizes increased rapidly with the increase of depth, while the Vickers hardness decreased with the increase of depth, and this phenomenon could be explained in terms of boundary strengthening and dislocation strengthening. The number fractions of medium-angle grain boundaries (MAGBs) and medium-high-angle grain boundaries (MHAGBs) in UFG zones were larger than those in the transition zone and the deformed zone. However, the number fraction of the low-angle grain boundaries (LAGBs) was extremely small in all the zones after SMAT, especially in the transition zone.

Materials (Basel) ; 11(11)2018 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-30404205


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.

Materials (Basel) ; 11(9)2018 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-30150511


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.