Papers by Keyword: CSL

Abstract: The present study investigates the occurrence and effectiveness of the dissociation mechanism of Σ3 CSL boundaries into its variants such as Σ9 and Σ27a-b during strain-annealed grain boundary engineering (GBE) of Hastelloy-X. Multiple cold-rolling strain levels and annealing conditions are studied and it is observed that the density of ∑3 boundaries decreases proportionally to the amount of strain induced boundary migration (SIBM) during the GBE process. The dissociation mechanism of Σ3 annealing twins is activated at the onset of SIBM, causing an increase in the density of the Σ3ⁿ variants. It is shown that at high annealing times or temperatures, the rate of generation of CSL boundaries through dissociation mechanism is lower than their annihilation rate. It is further suggested that the dissociation mechanism of ∑3 boundaries during GB migration is more efficient when the amount of applied strain prior to annealing is kept low, thus promoting disruption of the random GB network.

Abstract: In a trench MOSFET structure, p+ trench bottom implant (also called p+ shielding region) is commonly used to protect the gate oxide from high electric field stress, however, if the design and fabrication process are not optimized properly, the p+ shielding region together with n-drift and the p-base region will form a parasitic JFET which severely degrades the on-state performance of the device. This paper presents this parasitic JFET effect with experimental results and the optimization work that has been done to eliminate the parasitic JFET.

Abstract: To improve our understanding of the mechanisms of gold deposition, a comparison was made of the microstructures of a natural gold sample with a synthetic gold foil of similar alloy composition (approximately Au 90%, Ag 10%). The aim was to identify any similarities between the samples that could help increase our knowledge of how the natural gold microstructures formed and were modified post-mineralisation. The samples were analysed using electron backscatter diffraction to map their microstructure, with the synthetic gold foil then heated to and mapped at 400°C, 500°C, 600°C and 700°C. Both the natural and synthetic sample exhibited a dominance of ∑3 twin boundaries, but these were much less abundant in the synthetic sample prior to heating. The natural sample is dominated by coarse grains exhibiting lattice distortion and low angle grain boundaries, which more closely resemble the synthetic gold foil microstructure after recrystallisation has taken place, than the initial microstructure, implying that the grains have had time to grow. Performing experiments such as these allows direct comparison of gold microstructures where the formation conditions are known and the controlling mechanisms can be determined. This will improve our understanding of the important mechanisms behind gold deposition.

Abstract: Effect of coil temperature on the texture and microstructure evolution during cold rolling and annealing were investigated by OM, ODF and EBSD. The results indicate that the {223}<110> and {114}<110> textures appeared after cold rolling are inherited followed by annealing, whose intensities would be higher as the coil temperature decreased. Lower coil temperature could improve the uniformity of grain size and increase the fraction of low-angel grain boundaries as well as coincidence site lattice boundaries. And the {111}//ND texture is improved in the lower coil temperature cold and annealing steel sheet, which is beneficial for the deep-drawability.

Abstract: This paper deals with the investigation of grain boundary engineering processes in case of AISI 304 type austenitic stainless steel. The effects of the thermo-mechanical treatments for the modification of the grain boundary structure are demonstrated on the special grain boundaries. The proper thermo-mechanical treatments can increase the fraction of the CSL-boundaries. Since the CSL-boundaries are resistant against intergranular degradation processes, materials owning enhanced properties can be developed due to these treatments. The investigation of the grain boundary character distribution is carried out by automated electron back scattered diffraction (EBSD) measurements after different thermo-mechanical treatment processes. The effect of the heat treatment duration on the grain boundary structure is examined; the optimal treatment is represented. It is shown by experimental results, that the parameter settings of the evaluation method strongly influence the obtained results.

Abstract: AISI 304 type austenitic stainless steel samples were subjected to different thermomechanical treatments in order to investigate the effect of thermo-mechanical treatment on the grain boundary structure of the material. Electron back scatter diffraction measurements have been carried out in order to obtain information about the boundaries of the treated specimen. The measurements showed that achieving the same deformation with the same number of deformation cycles and same heat treatment temperature, the application of shorter heat treatment holding time was advantageous in aspect of grain boundary structure comparing to the thermo-mechanical treatments with longer holding time. The frequency of the special Σ3n type CSL-boundaries excluding coherent twin boundaries was significantly decreased by increasing the heat treatment holding time of the samples from the very short heat treatment periods. Extending the holding time further, the frequency of the special Σ3n type CSL-boundaries excluding coherent twin boundaries increased and reached the results applying the shorter heat treatment periods.

Abstract: Recrystallization texture in grain oriented silicon steel at different annealing temperature is investigated. Normalized x-ray intensities of various orientation components observed in Orientation Distribution Function are used for comparison. The computed CSL boundary distributions about Goss component with annealing condition were calculated. The misorientation angle distribution is also measured in order to find the importance of high-energy boundary with misorientation 20~45° range for the secondary recrystallization of Goss grain. From the analysis of CSL boundary distribution and misorienation angle distribution, the distribution of CSL boundaries does not evidently show any preferred difference between Goss and other texture components. Whereas, the misorientation angle analysis shows that the number of 20°~45° misoriented boundaries is higher around the Goss grains than around other texture components.

Abstract: Three different types of austenitic stainless steel (SUS 304, SUS 304L and SUS 316) samples were cold formed in order to investigate the effect of cold forming on the grain boundary structure of the material. SUS 304L and SUS 316 samples were cold rolled, SUS 304 samples were tensile loaded in different manner at room temperature. Electron back scatter diffraction measurements have been carried out in order to obtain information about the boundaries of the treated specimen. The measurements showed that the frequency of the special Σ3n type CSLboundaries was significantly decreased by increasing the deformation of the samples.