Surface damage induced by mechanical polishing of cold-rolled and annealed Pd specimens was examined by cross-sectional electron backscatter diffraction (EBSD) measurements. Fine grains with high-angle grain boundaries were detected in the outermost layer in both specimens. Less granular but layered gradation of crystallographic orientation was detected in the sub-surface layer of the annealed specimen. In the cold-rolled specimen, a lot of elongated grains were detected in the entire inner layer. The formation of the sub-surface layer seemed to be prevented in the cold-rolled specimen by pre-introduced microstructures. In the annealed specimen, the depth of the surface damage layer was dependent on the crystallographic orientation of the matrix grain. This study clearly demonstrated the application of cross-sectional EBSD analysis for evaluating surface damage in metallic materials.
Mater. Trans. 62 (2021) 41-47に掲載.Table 3, Figs. 1, 3, 4のキャプションを修正.
Cu fine-particle paste is a promising material to form a low-cost interconnect for flexible electronics devices. It has been reported that Cu particles can be sintered at low temperature (well below the half of the melting point) through two-step heat treatment processes of oxidation and reduction. However, the mechanism of the low temperature sintering is not clear yet. In this study, we investigated the oxidation sintering process of Cu fine particles by thermal gravimetric analysis (TGA) in the temperature range of 200-300℃, X-ray diffraction (XRD), and microstructural observation. It was found from TGA that the oxidation process was initially rate-controlled by surface reaction and then by Cu diffusion at grain boundaries of Cu2O. Transmission electron microscopy observation revealed the formation of a core (Cu)-shell (Cu2O) structure during the oxidation process. The adjacent Cu2O shells were bonded to each other resulting in a cross-linked structure. The subsequent reduction process led to the formation of a porous structure by oxygen removal, but the cross-linked structure was maintained, which would make the low-temperature sintered Cu body as robust as solidified solder and sintered Ag paste.
Young Author Best Paper Award 2023