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[en] The critical resolved shear stresses (CRSSs) and flow curves for the seven possible slip systems in Ti-6Al-4V with a lamellar microstructure were determined via high-temperature uniaxial compression testing. For this purpose, samples with a rectangular cross section were cut from single colonies grown using a float-zone technique and then tested at 815 deg. C. Each sample was oriented for single slip along one of seven different slip systems in the alpha phase; i.e., one of the three <112-bar 0>{101-bar 0} (prism < a>), the three <112-bar 0>{0001} (basal < a>), or the < c + a> (pyramidal) systems was activated by orienting specific samples to have the highest Schmid factor on that particular system. Measurements of the CRSS at yielding and the subsequent flow behavior revealed a strong dependence of mechanical behavior on colony orientation/activated slip system. The anisotropy in the CRSS and the tendency for flow softening at large strains was rationalized on the basis of the Burgers orientation relationship between the alpha (hcp) lamellae and the beta (bcc) matrix and hence the orientation of alpha slip directions relative to those in the beta phase.

[en] Physics-based models for predicting the mechanical behavior of Ni-based superalloys as a function of microstructure features require the use of microstructure data for calibration and verification. Accurate representation of the heterogeneity of microstructure features requires accurate selection of the representative microstructure data size (i.e. image size). Thus, this work is carried out to address the influence of microstructure data size on the accuracy of a discrete dislocation dynamic model in predicting the critical resolved share stress (CRSS) of IN100. Microstructure features from backscattered electron images were extracted using image processing techniques. Single point statistics (e.g. area fraction, precipitate size, and distance between γ' particles) and higher order statistics using two-point correlations were calculated from segmented 2-D images. Modified Bhattacharyya Coefficient analysis techniques were employed to calculate three-dimensional particle size distributions. Results indicate a significant influence of the microstructure data size on the calculated CRSS.

[en] The effect of preheat temperature and inter-pass reheating on microstructure and texture evolution during unidirectional hot rolling of Ti-6Al-4V in the alpha + beta field was investigated. Three different heating schedules were used to roll plates at 10% reduction per pass to a 3:1 total reduction (true strain = 1.15): (1) preheat at 955 deg. C with inter-pass reheating for 3 min, (2) preheat at 955 deg. C without inter-pass reheating, and (3) preheat at 815 deg. C with inter-pass reheating for 3 min. Following rolling, each plate was air cooled to simulate production practice. The microstructures and textures were determined using electron-backscatter and X-ray diffraction techniques. The results revealed that the intensity of basal poles decreased along the rolling direction and increased along the normal and transverse directions with decreasing rolling (furnace) temperature or the elimination of reheating between passes

[en] A method for separating the textures of primary alpha (α_p) and secondary alpha (α_s) in alpha/beta titanium alloys with a duplex microstructure was developed. Utilizing electron backscatter diffraction (EBSD) and energy-dispersive spectroscopy (EDS), the approach relies on the non-uniform partitioning of alloying elements between primary alpha and regions containing secondary-alpha lamellae and residual beta matrix phase. The method was evaluated using samples of Ti-6Al-4V for which vanadium partitions strongly to secondary alpha + beta regions. The technique thus provides a useful tool for quantifying the evolution of deformation texture in the primary alpha and transformation texture in secondary alpha formed via decomposition of the beta matrix following hot working or final heat treatment

[en] The purpose of this study was to evaluate the role of magnetic resonance spectroscopy (MRS) in nonlesional temporal lobe epilepsy. Subjective and methods: Between April 2011 and December 2013, a total of 30 patients having partial seizures with or without secondary generalization were selected from the Neurology Department, Sayed Galal Hospital, Al Azhar University and were studied in this work. All patients included in the study had clinical history, seizure symptoms, inter-ictal electro encephalography and neuroimaging findings that were consistent with non-lesional epilepsy of temporal lobe origin. We mean by non-lesional epilepsy that those cases are not secondary to other pathological lesions e.g. tumor, vascular insult or post inflammatory. Mesial temporal sclerosis was considered as nonlesional temporal lobe epilepsy. Each patient was thoroughly asked about the detailed clinical history after reviewing the referring imaging request and laboratory findings. The MRI and MRS examinations were performed in all the patients in one session. They were performed at 1.5 T super conducting system. Results: MRS was performed in a total of 30 patients. Sixteen patients were males and 14 were females. The average age of the patients was 32 years (range: 17-47 years). Seventeen patients (56.7% of total patient number) were found to have clinical and EEG criteria of epileptic activity related to temporal lobe origin on the right side, while 11 patients (36.7% of total patient number) were found to have these findings on the left side. Two patients (6.6% of total patients number) were having bilateral temporal lobe epileptic activity. Twenty six patients (about 87% of total patient number) were able to be lateralized with MRS using asymmetry index, 16 cases lateralized to the right side (about 53% of total patient number) and 10 cases lateralized to the left side (about 34% of total patient number). The remaining 4 patients (about 13% of total patient number) failed to be lateralized in our study. The sensitivity and specificity of the Conventional MRI and MR spectroscopy for detection of mesial temporal lobe epilepsy were 60% and 65% and 86% and 83% respectively. Conclusion: MR spectroscopy is a very sensitive guiding tool in predicting the temporal lobe epilepsy (TLE) and the side of involvement in patients with TLE even in patients with MR negative studies. It helps in detecting abnormal spectra of various brain metabolites. MR spectroscopy has demonstrated consistent metabolic abnormalities in partial seizures. MRS can also detect bilateral affection with the ipsilateral side more affected

[en] Research highlights: → EBSD analysis of cold-rolled titanium revealed three stages of structure evolution. → These stages are defined by plots of the boundaries density as a function of strain. → The first stage is associated with twinning. → Dislocation density increases and substructure forms at the second stage. → The third stage is related to the formation of high-angle boundaries. - Abstract: The evolution of microstructure in commercial-purity titanium during cold rolling to a thickness strain of 2.6 was quantified using electron backscatter diffraction. The measurements were analyzed in terms of the mean grain size and the density of boundaries (the ratio of total boundary length to the scanned area). The density of high-angle boundaries as a function of thickness strain had three distinct stages, each of which was associated with a different mechanism of microstructure formation, i.e., (i) twinning, (ii) an increase in dislocation density and the formation of substructure, and (iii) the formation of deformation-induced high-angle boundaries. The influence of twinning on the kinetics of microstructure evolution was also interpreted.

[en] High-resolution X-ray diffraction (XRD) line-profile analysis was used to characterize slip activity and twinning in commercial-purity titanium (CP-Ti) during hot rolling. The effect of {10.1} and {10.2} twins on XRD patterns was deduced using the DIFFAX software. The density of twin boundaries was then incorporated into the XRD pattern-fitting procedure for evaluating dislocation densities, slip activity, and subgrain size. It was found that < a> and < c + a> type slip occurred during hot rolling. The X-ray data revealed 0.07(±0.02)% twin-boundary frequency for the {10.2} twin family, but zero twinning (within the experimental accuracy) in the {10.1} family. Electron backscatter diffraction (EBSD) data confirmed the X-ray findings

[en] High-resolution electron back-scatter diffraction (EBSD) analysis was employed to establish mircostructure evolution in heavily cold-rolled alpha-titanium. After thickness reductions of 75% to 96%, significant microstructure and texture changes were documented. The surface area of high-angle grain boundaries was almost tripled, thus giving rise to an ultra-fine microstructure with a mean grain size of 0.6 μm. Moreover, orientation spread around typical ‘split-basal’ rolling texture substantially increased. These effects were suggested to be related to the enhancement of pyramidal 〈c+a〉 slip