Papers by Author: F. Lin

Abstract: A new procedure is proposed for the exit electron wave reconstruction using a small set of high-resolution electron microscopy (HREM) images. This procedure is similar to that proposed by van Dyck and coworkers, but the relative shifts between different HREM images are obtained via the genetic algorithm instead of the more widely used cross-correlation function (XCF) method. The new procedure is demonstrated using simulated HREM images with added noise, and shown to be able to deal with situation where the scheme based on the method of XCF is not applicable.

Abstract: A Monte Carlo Potts model has been used to investigate cube-texture strengthening during grain growth in rolled high-purity Ni-tapes. The initial conditions for the simulations have been taken from electron back-scatter pattern (EBSP) orientation maps of already fully recrystallized samples. Experimentally, grain growth leads to an increase in the cube volume fraction to >95% , accompanied by an approximately ten-fold increase in the grain size. High cube volume fractions can be predicted under a number of conditions, though a small surface energy advantage of just 2% for cube-oriented grains is required to match the texture strengthening to the grain size change. An additional issue of interest is the influence on the grain growth of the large area-fraction of twin boundaries in the fully recrystallized condition. The presence of boundaries with low energy has a strong influence on the simulated microstructural evolution.

Abstract: After primary recrystallization of highly rolled (>98% reduction) high purity Ni (99.999%) tapes the cube texture fraction can range from 45 - 65%. Annealing at temperatures >1000oC leads to cube texture volume fractions of >95% as a result of grain growth. A Monte Carlo Potts model was used to simulate this annealing process. The starting microstructures for the simulations were generated from experimental data taken using electron backscatter pattern analysis. The simulation results suggest that in addition to the grain boundary misorientation and energy functions used, the misorientation texture and grain sizes are also determining factors in the grain growth process. As the grain size after recrystallization is comparable to the tape thickness, the surface energy of the grains may also be an important factor. Simulations were therefore also carried using a surface energy term. If the cube grains have a lower surface energy then a stronger cube texture is predicted.