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We elucidate here the underlying reasons for the yield point elongation (YPE) phenomenon in medium-Mn steel. The cold-rolled Fe-0.2C-11Mn-2Al steel was subjected to controlled annealing temperature and soaking time such that YPE of different lengths was obtained. It was observed that the ultra-fine grained or globular microstructure is not the critical factor responsible for YPE. YPE is a consequence of close competition between the work hardening (via martensitic transformation) and softening (by stress relaxation and transfer) induced by the TRIP effect. The ferrite grains with γ fiber have the potential to have high dislocation storage ability, with consequent increase in dislocation density and work hardening exponent, leading to decrease of YPE.

The formation of highly-twinned ultrafine austenite on a cold rolled AISI 316L steel induced by low energy high current pulsed electron beam (LEHCPEB) treatment has been investigated. It is shown that rapid phase transformation, recrystallization and recovery can be achieved simultaneously through pulsed electron beam treatments under heating mode without melting the surface. The extremely fast thermo-mechanical cycles induced by the LEHCPEB account for the surface austenization and the formation of ultrafine twins. The results demonstrated that pre-deformation combined with LEHCPEB treatment under heating mode can be used to create ultrafine microstructures with special boundary characteristics in the surface layer.

Three sets of model predicted values for speciated mercury concentrations and dry deposition fluxes over the Great Lakes region were assessed using field measurements and model intercomparisons. The model predicted values were produced by the Community Multiscale Air Quality Modeling System for the year 2002 (CMAQ2002) and for the year 2005 (CMAQ2005) and by the Global/Regional Atmospheric Heavy Metals Model for the year 2005 (GRAHM2005). Median values of the surface layer ambient concentration of gaseous elemental mercury (GEM) from all three models were generally within 30% of measurements. However, all three models overpredicted surface-layer concentrations of gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) by a factor of 2-10 at the majority of the 15 monitoring locations. For dry deposition of GOM plus PBM, CMAQ2005 showed a clear gradient with the highest deposition in Pennsylvania and its surrounding areas while GRAHM2005 showed no such gradient in this region; however, GRAHM2005 had more hot spots than those of CMAQ2005. Predicted dry deposition of GOM plus PBM from these models should be treated as upper-end estimates over some land surfaces in this region based on the tendencies of all the models to overpredict GOM and PBM concentrations when compared to field measurements. Model predicted GEM dry deposition was found to be as important as GOM plus PBM dry deposition as a contributor to total dry deposition. Predicted total annual mercury dry deposition were mostly lower than 5 μg m(-2) to the surface of the Great lakes, between 5 and 15 μg m(-2) to the land surface north of the US/Canada border, and between 5 and 40 μg m(-2) to the land surface south of the US/Canada border. Predicted dry deposition from different models differed from each other by as much as a factor of 2 at regional scales and by a greater extent at local scales.

The mechanisms of corrosion and wear improvements by low energy high current pulsed electron beam (LEHCPEB) have been investigated for an AISI 316 L steel. Selective purification followed by epitaxial growth occurred in the top surface melted layer (2–3 μm thick) that was softened by tensile stresses and, to a much lower extent, by lower efficiency of MnS precipitation hardening. Electrochemical impedance spectroscopy and potentiodynamic polarization analyses used to model the corrosion behavior revealed that, while craters initiated at MnS inclusions initially served as pitting sites, the resistance was increased by 3 orders of magnitude after sufficient number of pulses by the formation of a homogeneous covering layer. The wear resistance was effectively improved by sub-surface (over 100 μm) work hardening associated with the combine effect of the quasi-static thermal stress and the thermal stress waves. The overall results demonstrate the potential of the LEHCPEB technique for improving concomitantly the corrosion and wear performances of metallic materials.

We investigated a two-week episode with high PM concentrations in California Central Valley during the Christmas–New Year of 2000–2001 using a modeling system that consists of a computationally efficient, 3-D photochemical–microphysical transport model, a mesoscale meteorological model, emission models, and an evaluation package. One hundred simulations were conducted with fine resolutions and observational constraints, to reproduce spatial and temporal features of observed PM concentrations and to understand the formation mechanism of the episode. Simulated PM concentrations consist of secondary inorganic components, mainly ammonium nitrate, and total carbon in areas with elevated concentrations in the accumulation mode, and consist of mainly dust and sea salt in the coarse mode. Simulated oxidants and nitrate were significantly elevated over the valley, and the latter showed much less amplitude than the former. Simulated PM concentrations were evaluated with observations systematically with spatially and temporally paired method, a more restrictive multivariate method (NMFROC), and a more flexible “gradient evaluation” method. The paired evaluation shows that high correlation coefficient (R = ∼0.8) and low fractional error (FE = ∼0.1) could be achieved at stations with elevated 24-h concentration of PM in the accumulation mode in some simulations. The NMFROC method was used to extract useful information from seemingly failed simulations. A “gradient evaluation” method is introduced here to extract additional information from simulations. We found that emission reductions of NOx and AVOC showed similar effects on percentage basis in different areas, and both are more effective than reducing NH3 for abating elevated concentrations of accumulation mode PM in California Central Valley during the winter episode.

A detailed analysis from cross-section of the rapidly solidified layer of a steel formed by low energy high-current pulsed electron beam (LEHCPEB) treatment has been successfully carried out. The results of electron backscattering diffraction (EBSD) measurements revealed that the microstructures and phase components vary dramatically through the melted layer and the heat-affected zone. The exact nature of such a graded structure also changes with the number of pulses. The phase transformation paths vary at different depth and different areas (close to or far away from the carbides). They are determined both by (i) the temperature gradients and (ii) the composition gradients in the surface layers induced by the LEHCPEB treatment.

Electron backscatter diffraction has been used to study the severe plastic deformation occurring in the surface layer of an AISI 316L stainless steel treated by high-current pulsed electron beam (HCPEB). The exact nature of the triggered mechanisms was orientation-dependent. In particular, twinning was activated in grains having 〈1 1 1〉 orientation close to the sample normal direction while high misorientation deformation gradients were created by intense crystallograplic slip in some other grains. The nature of the different deformation mechanisms and their orientation dependence are discussed both from theoretical and experimental points of views by considering the biaxial quasi-static thermal stresses generated during the HCPEB bombardment.

A simple but self-consistent scheme is proposed for studying the electronic structure of graphite acceptor compounds (GAC). The basic concept of the computor renormalization group (CRG) is applied in simplifying the interactions between graphite and the intercalants, and a “pseudo-atom” is used to simulate the intercalant molecule. This model enables us to study different IC 8 type GAC in the same program, the extended Huckel energy band method is developed and the resulting band structures and Fermi surface properties of GAC (FeCl 3 , AsF 5 ) thus obtained are discussed and compared with the present data.

A cluster model is proposed. The most stable geometry of LiC 6 is determined by minimizing the total energy of the cluster calculated by the charge self-consistent EHT method. The charge transfer between Li and C, and the density of states are calculated. It is found that LiC 6 is a donor compound with metallic properties. According to the SCF charge transfer, the modified ionization potential of different atoms in the cluster can also be worked out and can be used as parameters for the tight-binding band calculation.