changrun cai - Academia.edu (original) (raw)

Papers by changrun cai

A near-surface layer existed on a cold rolled and annealed foil stock AlFeSi alloy due to severe ... more A near-surface layer existed on a cold rolled and annealed foil stock AlFeSi alloy due to severe shear strain during twin-roll casting and subsequent cold rolling. The near-surface layer, with a thickness up to ~ 700 nm and consisting of ultrafine grains with diameters up to 100 nm and high population of voids/microcracks, was present as randomly distributed patches on the alloy surface. The grain boundaries within the near-surface layer were decorated by oxide particles and inclusions of lubricant residue, which reduce the ductility of the near-surface layer. During sheet forming, further shear deformation occurred in the near-surface region due to the friction caused by the sliding contact between the alloy sheet and the forming tool. The differences in the microstructure and the ductility between the near-surface layer and the underlying bulk alloy resulted in cracking within the near-surface layer and/or at the near-surface layer/bulk alloy interface, finally leading to the delamination of patches of the near-surface layer. The delamination generated flake-like alloy debris may significantly modify the property of forming lubricant and influence the tendency to galling during sheet forming.

aqueous reaction to form the hydrated fluorides which are subsequently dehydrated at elevated tem... more aqueous reaction to form the hydrated fluorides which are subsequently dehydrated at elevated temperatures in an atmosphere of HF gas. Extensive studies were made of the conditions for the preparation of high-purity ZrF4, and pilot plant equipment is described which was used to prepare 100 lb batches of the fluorides. The reduction step was investigated thoroughly, particularly for Zr, and those factors which affect metal quality and yield were determined. Reduction yields of 96 % were obtained with both Zr and Hf. After are-melting, the sponge Zr had a hardness of 40-45 Rockwell A and was readily cold-rolled into sheet. Zr metal thus prepared had a purity of about 99.8%. Hf metal, similarly prepared, had a hardness of 69 Rockwell A and was hot-rolled but was too brittle to be easily cold worked. The Hf was low in metallic impurities, but contained considerable amounts of C, N, and oxygen. ACXNOWLI~DGMENTS The authors are especially grateful to J. W. Starbuek for his valuable contribution in the experimental redue-tion studies, to B. A. LaMont and co-workers for the chemical analyses, and to C. Lentz and associates for the spectrographic analyses. ABSTRACT At low overvoltage values, deviations from Tafel behavior for a noncorroding electrode are due primarily to the reverse reaction of the oxidation-reduction system, and at high overvoltages to concentration and/or resistance polarization. It is shown further that the practice of placing straight lines through a few experimental points is extremely hazardous, while the indiscriminate introduction of "breaks" is contrary to the electrode kinetics described. Further complexities arising from a corroding electrode are described. In this instance , the forward and reverse reactions of both of the oxidation-reduction systems forming the corrosion couple must be considered. This representation of the local polarization diagram of a corroding metal is more fundamental than that used previously in the literature, and thus provides a clearer picture of the various factors which affect the corrosion rate and the shape of polarization curves. A region of linear dependence of potential on applied current is described for a corroding electrode by treating it in a manner analogous to that for a noncorroding electrode. An equation is derived relating the slope of this linear region to the corrosion rate and Tafel slopes. This relation provides an important new experimental approach to the study of the electrochemistry of corroding metals since, in some instances, interfering reactions prevent determination of T~fel slopes at higher current densities. Polarization measurements are an important research tool in investigations of a variety of electrochemical phenomena. Such measurements pernfit studies of the reaction mechanism and the kinetics of corrosion phenomena and metal deposition. In spite of their wide applicability and extensive use, considerable uncertainty in the interpretation of polarization measurements still exists. Some of the uncertainties include the proper method of plotting data and the correct interpretation of "breaks" in polarization curves. Abrupt changes in slope of overvoltage vs. log current have been given considerable significance in the past few years. Logan (1) examined various methods of plotting cathodic polarization measurements to evaluate the correspondence between current required for complete cathodic protection of a system and current flow at the potential break. He reported that the potential break) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.88.117.172 Downloaded on 2016-01-28 to IP

A correlation has been revealed between the localised corrosion susceptibility and the grain stor... more A correlation has been revealed between the localised corrosion susceptibility and the grain stored energy in AA2099-T8 aluminium alloy, with grains of higher stored energy being relatively more susceptible to corrosion attack. The grains of high stored energy contain increased crystallographic defects, which could consequently decrease their corrosion resistance. Additionally, since crystallographic defects are preferential sites for the precipitation of T 1 (Al 2 CuLi) phase, it is suggested that grains of high stored energy could also contain increased volume fraction of T 1 phase after aging, which might further increase corrosion susceptibility due to the electrochemically high activity of lithium rich T 1 phase.