Electron backscatter diffraction in materials characterization

Electron Back-Scatter Diffraction (EBSD) is a powerful technique that captures electron diffraction patterns from crystals, constituents of material. Captured patterns can then be used to determine grain morphology, crystallographic orientation and chemistry of present phases, which provide complete characterization of microstructure and strong correlation to both properties and performance of materials. Key milestones related to technological developments of EBSD technique have been outlined along with possible applications using modern EBSD system. Principles of crystal diffraction with description of crystallographic orientation, orientation determination and phase identification have been described. Image quality, resolution and speed, and system calibration have also been discussed. Sample preparation methods were reviewed and EBSD application in conjunction with other characterization techniques on a variety of materials has been presented for several case studies. In summary, an outlook for EBSD technique was provided

Microstructure evolution in deformed and recrystallized electrical steel

A processing route has been developed for recovering the desired lambda fiber in ironsilicon electrical steel needed for superior magnetic properties in electric-motor application. The lambda fiber texture is available in directionally solidified iron-silicon steel with the columnar grains but was lost after heavy rolling and recrystallization required for motor laminations. Two steps of light rolling each followed by recrystallization were found to largely restore the desired fiber texture. This strengthening of the fiber texture had been predicted on the basis of the strain induced boundary migration mechanism during recrystallization of lightly rolled steel from existing grains of near the ideal orientation, due to postulated low stored energies. Taylor and finite element models supported the idea of the low stored energy of the lambda fiber grains. A novel methodology has been developed for converting the nanoindentation loaddisplacement data into indentation stress-strain curves and extracting the elastic and postelastic behavior. Extracted variations of effective indentation modulus with orientation were in excellent agreement with previously developed model. Furthermore, an intrinsic orientation dependence of indentation yield strength was extracted in a strain-free material. Developed nanoindentation methodology was successfully used for characterization of microstructure evolution in terms of stored energy variation with orientation during plane strain compression. Variations in stored energy at the grain-scale level were extracted from an increment in indentation yield due to increase in dislocation density. It was found that nanoindentation yield strength is about 2 times the yield strength of homogeneous compression. Moreover, higher indentation yield strength was observed in regions that have rotated during deformation to non-lambda orientations with higher Taylor factors. Experimental results have supported idea of correlation between the Taylor factor and stored energy that was used in multistage processing for successful recovery of lambda texture. Hypothesis for observed much higher strain hardening in nanoindentation than in homogeneous plane strain compression is that the rate of generation of new dislocations is dependent on the dislocation density alone while the rate of annihilation of dislocation is strongly dependent on both dislocation density and the type of dislocations being generated which can be influenced by deformation mode.Ph.D., Materials Science and Engineering -- Drexel University, 200

Raptor packets: a packet-centric approach to distributed raptor code design

In this paper, we address the problem of distributed Raptor code design over information packets located across the network nodes. We propose a novel approach to this problem that consists of generating, encoding and dispersing Raptor packets across the network. Unlike recent node-centric proposals, where network nodes are responsible for collecting information packets and performing Raptor encoding, in the proposed packet-centric approach this task is assigned to Raptor packets. In a two-step encoding procedure that corresponds to precoding and LT-coding step of standard Raptor encoding, Raptor packets randomly traverse the network, collect and encode sufficient number of information packets following exactly a given degree distribution, and finish their paths in a random network node. The efficiency of the distributed Raptor coding scheme is confirmed by simulation results, where their performance is demonstrated to approach closely the performance of standard (centralized) Raptor codes

Thermomechanical processing for recovery of desired < 001 > fiber texture in electric motor steels

A processing route has been developed for recovering the desired lambda fiber in iron-silicon electrical steel needed for superior magnetic properties in electric motor application. The lambda fiber texture is available in directionally solidified iron-silicon steel with the < 001 > columnar grains but was lost after heavy rolling and recrystallization required for motor laminations. Two steps of light rolling each followed by recrystallization were found to largely restore the desired fiber texture. This strengthening of the < 001 > fiber texture had been predicted on the basis of the strain-induced boundary migration (SIBM) mechanism during recrystallization of lightly rolled steel from existing grains of near the ideal orientation, due to postulated low stored energies. Taylor and finite element models supported the idea of the low stored energy of the lambda fiber grains. The models also showed that the lambda fiber grains, though unstable during rolling, only rotated away from their initial orientations quite slowly