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An alloy containing 5 at.% of N was produced by arc melting of Ti and TiN powders. By anodization of the alloy in a 10 wt.% KHPO/glycerol electrolyte at 140 °C, oxide mesosponge layers can be formed with thickness as up to several micrometers. X-ray photoelectron spectroscopy confirms nitrogen uptake in the oxide. Photoelectrochemical measurements show successful N-doping of these mesoporous anodic layers with a significant visible light photoresponse. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical corrosion behaviour of Type 304 and 316L stainless steels was studied in Hanks’ solution, Eagle’s minimum essential medium (MEM), serum containing medium (MEM with 10% of fetal bovine serum) without cells, and serum containing medium with cells over a 1-week period. Polarization resistance measurements indicated that the stainless steels were resistant to Hanks’ and MEM solutions. Type 304 was more susceptible to pitting corrosion than Type 316L in Hanks’ and MEM solutions. The uniform corrosion resistance of stainless steels, determined by R p, was lower in culturing medium than in Hanks’ and MEM. The low corrosion resistance was due to surface passive film with less protective to reveal high anodic dissolution rate. When cells were present, the initial corrosion resistance was low, but gradually increased after 3 days, consistent with the trend of cell coverage. The presence of cells was found to suppress the cathodic reaction, that is, oxygen reduction, and increase the uniform corrosion resistance as a consequence. On the other hand, both Type 304 and 316L stainless steels became more susceptible to pitting corrosion when they were covered with cells. [Copyright &y& Elsevier]

The semiconductor properties of passive films formed on an Fe–18Cr alloy with various additive elements in a borate buffer solution were studied using electrochemical impedance spectroscopy and photoelectrochemical response. The photocurrent was plotted as a photoelectrochemical action spectrum that could be separated into two components, which were mainly derived from Cr oxide (Eg=3.4 eV) and Cr hydroxide (Eg=2.4 eV). The band gap energy, Eg, of each component was almost constant, independent of the species and amount of additive elements. The photoelectrochemical response showed positive photocurrent for most potential in the passive region, which indicates that the passive film behaved as an n-type semiconductor. In addition, the Mott–Schottky plot of the capacitance showed positive slope, which also means that the passive films behaved as an n-type semiconductor. The donor density of the passive films, which can be estimated by the Mott–Schottky plots, changes depending on the film formation potentials and a variety of additives. [Copyright &y& Elsevier]

Aging behavior of an ultrafine grained Al–Cu alloy was studied. Al–2 wt%Cu alloy sheets were solution-treated at 550 °C for 1.8 ks and then severely deformed up to an equivalent strain of 4.8 by the accumulative roll bonding (ARB) process at ambient temperature. The ARB processed material showed the ultrafine lamellar boundary structure with mean boundary interval of 67 nm. The ARB processed sheets and the starting sheets having conventionally coarse grains were aged at 190 °C. The coarse grained specimen for comparison showed typical aging behavior showing in-grain precipitation of the thin-plate shaped θ′ phase coherent to {001} crystallographic plane of the matrix aluminum. Hardness of the coarse grained specimen increased as precipitation proceeds, reached the maximum around HV60, and decreased owing to over-aging. On the other hand, the ARB processed sample with the ultrafine-grained structure showed very high hardness of HV115 in the as-deformed state, and the hardness decreased monotonously with increasing the aging time. The detailed microstructural observations clarified that recovery and grain growth of the matrix proceeds during 190 °C aging and the precipitation only at grain boundaries occurs in the ultrafine grained material. Instead of the θ′ phase, the equilibrium θ phase preferentially appeared in the ultrafine grained specimen. The coarsening of the matrix was mainly responsible for monotonous decrease of hardness. The kinetics of precipitation in the ARB processed sample was much faster than that of the coarse grained materials. It was concluded that the aging behaviors in severely deformed material having the ultrafine grained structure are completely different from the conventional ones in the coarse-grained materials. [Copyright &y& Elsevier]

Anodization of near-equiatomic Ti-Ni alloys was performed in an ethylene glycol based electrolyte under various conditions in order to investigate the effects of crystal structure and chemical composition of the Ti-Ni alloy on the morphology of the resulting oxide layers. X-ray diffraction patterns revealed that Ti-Ni substrates with Ni content lower than 50.0 at.% were in the martensitic phase, while substrates with Ni content higher than 50.0 at.% were in the austenitic phase. Oxide layers formed at 20 or 35 V for 5 min exhibited no distinct nanotubular structures; however, at 50 V, nanotubular oxide layers were formed. After anodization at 50 V for 20 min, the growth of an irregular-shaped porous layer underneath the nanotubular oxide layer was observed for Ti-Ni alloys with Ni content lower than 52.2 at.%, whereas the oxide layer consisted of only irregular-shaped porous structures for the Ti-52.5 at.% Ni alloy. Further anodization resulted in the formation of irregular-shaped porous oxide layers on all Ti-Ni alloys examined. Energy-dispersive X-ray analysis indicated that this morphological transition is related to Ni accumulation in the vicinity of the interface between the bottoms of the oxide layers and the surfaces of the substrate alloys. Therefore, nanotubular oxide layers cannot be grown, and instead irregular-shaped porous oxide layers are formed underneath the nanotubular layers. These results indicate that the morphology of anodic oxide layers formed on the near-equiatomic Ti-Ni alloys is not affected by their crystal structure, but by Ni content and anodization time. [ABSTRACT FROM AUTHOR]