Papers by Author: Wei Guo Wang

Abstract: A wedge-shaped 304 austenitic stainless steel with varied thickness longitudinally was cold rolled into a flat one and then annealed at 1323K for 10 min. The grain boundary character distributions (GBCDs) in the specimen as processed were examined by the means of Electron backscatter diffraction (EBSD). The results showed that, at the regions with low pre-strains ranged from 4% to 6%, quite high fractions of S3ⁿ (n=0,1,2,3) grain boundaries and large-sized S3ⁿ (n=0,1,2,3) grain clusters are introduced compared with the regions of quite low ( less than 2.5%) or relatively high pre-strain. The surface appearance of after corrosion test reveals that grain dropping due to intergranular corrosion (IGC) is depressed and the penetration of IGC from the surface into the interior in the cross-section is arrested significantly as well in the regions with high fractions of S3ⁿ boundaries and large-sized S3ⁿ grain clusters.

Abstract: The grain boundary character distributions (GBCDs) of two 304-type austenitic stainless steel samples, which are cold rolled with the same thickness reduction of 6% and then subjected to different annealing treatments are examined by Electron back-scatter diffraction (EBSD) techniques. The results indicate that, after 6% cold rolling, the two-step annealing (900°C/1 h+1050°C/5 min, Sample B) resulted in a quite different GBCDs compared with that obtained by single-step annealing (1050°C/5 min, Sample A) regardless of nearly the same fractions of S3 boundaries developed in the two samples. It was evidenced that large-sized cluster of grains interfaced by S3n boundaries (S3n CG) emerged in sample B, in which there are moderate preferential grain orientation distribution and {111} grain boundary plane distributions. Further discussions highlighted that, in the case of two-step annealing, the first annealing at relatively low temperature (900°C) for short time (1h) contributes a lot to the final optimization of GBCD and strain induced preferential boundary migration (SIBM) accompanied by multiple twinning via the migration and interactions between mobile S3n boundaries, especially incoherent S3 boundaries, might be the responsible mechanisms.

Abstract: Five samples of Pb-Ca-Sn-Al alloy with different initial microstructures were processed in the same way including cold rolling with thickness reduction of 30% at the temperature of liquid nitrogen and then annealing at 270oC (0.9Tm) for 1 to 10 minutes. Electron back-scatter diffraction (EBSD) analyses indicated the initial microstructure which is at the end of primary recrystallization with a averaged grain size around 10 microns, a fair quantity of annealing twins and a random orientation can definitely result in a final grain boundary character distribution (GBCD) mainly composed of special boundaries (SBs) of which its fraction is higher than 75%, and the averaged SB cluster size exceeds 200 microns, implying the GBCD is optimized in satisfaction. However, the initial microstructures of partial recrystallization or full recrystallization but with coarser grain size are not good at producing high fraction SBs, whereas the initial microstructure of deformation with very strong textures is harmful to the formation of SBs in the processing of rolling followed by annealing. High resolution EBSD measurements revealed that the interactions between mobile incoherent ∑3 boundaries which were probably introduced by the continuous recrystallization from the distorted coherent ∑3 ones could be the formation mechanisms of the GBCD containing high fraction SBs.

Abstract: Grain boundary character distributions (GBCD) of type 304 stainless steel cold rolled and then annealed at 1173K were analyzed by electron back scatter diffraction (EBSD). The results showed that low strain (~6%) followed by long-time annealing (96h) resulted in a GBCD containing a high fraction of Σ9 and Σ27 boundaries. The connectivity of general high angle grain boundary (HAB) network was interrupted significantly by Σ3n(n=1,2,3) boundaries(special boundaries).

Abstract: The progress of grain boundary engineering (GBE) is overviewed and the challenges for further investigations emphasized. It points out that, the electron backscatter diffraction (EBSD) reconstruction of grain boundaries, which gives the information of connectivity interruption of general high angle boundaries (HABs), is more significant than purely pursuing high frequency of so-called special boundaries. The criterion for the optimization of grain boundary character distribution (GBCD) needs to be established. The energy spectrum and the degradation susceptibility of grain boundaries of various characters including HABs and low Σ（Σ≤29） coincidence site lattice (CSL) needs to be studied and ascertained. And finally, the newly proposed model of non-coherent Σ3 interactions for GBCD optimization are discussed.