A series of experimental studies are carried out to investigate the steady-state microstructures and mechanical properties of Cu, Ni, and Al obtained by equal-channel angular pressing (ECAP) at homologous temperatures. Under 0.32T_m the steady-state grain sizes d_s of the three metals are below 1 μm, and dominated by dynamic recovery mechanism. Discontinuous dynamic recrystallization (DDRX) occurs in Cu and Ni processed by ECAP at 0.4T_m. The variation of dislocation density at 0.32T_m (ρ_Cu>ρ_Ni>ρ_Al) shows a dependence on stacking fault energy (SFE), and it is consistent with the change of kernel average misorientation (KAM) values (Cu > Ni > Al). The SFE not only influences the strain hardening capacity of metals but also the critical strain needed to get steady-state. In order to understand the relationship between SFE and d_s quantitatively, a steady-state grain size model based on the Mohamed’s dislocation model is proposed through considering dynamic recovery mechanisms. Two important factors temperature and SFE are involved in the model, and other parameters and constants are determined from our experimental data. The predictions of d_s by the model are compared with d_s obtained by experiments for five fcc pure metals (Au, Ag, Cu, Ni, and Al), and the characteristic and limitation of the model are discussed.

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.

Computer Simulation of Helium Effects in Plutonium During the Aging Process of Self-Radiation Damage - Volume 11 Issue 4 - Bingyun Ao, Piheng Chen, Peng Shi, Xiaolin Wang, Wangyu Hu, Liang Wang

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.