Perpendicular Grain Boundary Research Articles

Comparison of fatigue lives between grain boundaries and component single crystals of copper bicrystals

Abstract Fatigue lives of grain boundaries (GBs) and component crystals were measured by using [123]/[335] and [5 9 13]/ [579] Cu bicrystals with a perpendicular GB at room temperature in air. The results show that the GBs were always the preferential sites for fatigue crack initiation and propagation in the two groups of bicrystals under cyclic tensiontension loading as well as push-pull straining control. When an [123]/[335] bicrystal with reduced section area was tested by cyclic tension-tension loading, the [335] component crystal always had a relatively higher fatigue life than the [123] component crystal. As a result, the fatigue life increased in the order of GB, [123] and [335] component crystals. When the two groups of bicrystals were subjected to cyclic push-pull straining, the GB of the [5 9 13]/[579] bicrystal showed a higher fatigue life than that of the [123]/[335] bicrystal, which was suggested to be partially attributed to the difference in the component crystal orientations in the two bicrystals. By using scanning electron microscopy and electron channeling contrast techniques, the fatigue damage features on the surfaces and fatigue fractography were examined. Based on the present results, the fatigue cracking mechanisms along GBs and persistent slip bands in Cu bicrystals are discussed.

Effect of grain boundary direction on blistering in deuterium-exposed tungsten materials: Parallel grain boundary versus perpendicular grain boundary

The effect of grain boundary (GB) direction with respect to the exposed surface on blistering in tungsten (W) is studied. Four types of W materials were used in this work and classified according to GB directions: one with GBs parallel to the exposed surface (parallel GBs) and the other with GBs perpendicular to the exposed surface (perpendicular GBs). After exposure to high flux deuterium plasmas, blisters were observed and found to be related to GBs in all types of materials. It is found that large-size blisters were originated from parallel GBs rather than perpendicular GBs. Blisters were supposed to grow faster in parallel GBs than in perpendicular GBs. Moreover, the exfoliation of blister caps was observed in the materials with parallel GBs but not in that with perpendicular GBs. This study provides a new insight into the role of GB direction on blistering.

High-Performance Recessed-Channel Germanium Thin-Film Transistors via Excimer Laser Crystallization

This letter demonstrates the excimer laser crystallization (ELC) of germanium (Ge) thin films with the recessed-channel (RC) structure for high-performance p-channel Ge thin-film transistors (TFTs). Using ELC, large longitudinal grains with a single perpendicular grain boundary (GB) in the center of the recessed region were formed. This can be attributed to the lateral grain growth from un-melted Ge solid seeds in the thick region toward the complete melting recessed region during ELC. Consequently, the proposed p-channel RC-ELC Ge TFTs possessing large longitudinal grains without the perpendicular GB in the channel region exhibited a superior field-effect hole mobility of 447 cm2V−1s−1 with minor performance deviation.

Comparison of fatigue lives between grain boundaries and component single crystals of copper bicrystals

Fatigue lives of grain boundaries (GBs) and component crystals were measured by using [123]/[335] and [5 9 13]/ [579] Cu bicrystals with a perpendicular GB at room temperature in air. The results show that the GBs were always the preferential sites for fatigue crack initiation and propagation in the two groups of bicrystals under cyclic tension-tension loading as well as push-pull straining control. When an [123]/[335] bicrystal with reduced section area was tested by cyclic tension-tension loading, the [335] component crystal always had a relatively higher fatigue life than the [123] component crystal. As a result, the fatigue life increased in the order of GB, [123] and [335] component crystals. When the two groups of bicrystals were subjected to cyclic push-pull straining, the GB of the [5 9 13]/[579] bicrystal showed a higher fatigue life than that of the [123]/[335] bicrystal, which was suggested to be partially attributed to the difference in the component crystal orientations in the two bicrystals. By using scanning electron microscopy and electron channeling contrast techniques, the fatigue damage features on the surfaces and fatigue fractography were examined. Based on the present results, the fatigue cracking mechanisms along GBs and persistent slip bands in Cu bicrystals are discussed.

Grain boundary effects on the fatigue deformation and cracking behavior of copper bicrystals

Fatigue tests were performed on two types of [134] iso-axial copper bicrystals for studying the grain boundary (GB) effects on the cyclic deformation and fatigue cracking behavior and the corresponding mechanism in copper bicrystals. One bicrystal contains a perpendicular GB and the other contains a tilting one with respect to the loading axis. Both the grain boundaries are nearly 180° rotated. It was shown that both the perpendicular and tilting grain boundaries have little effect on the cyclic hardening and saturation behavior of the bicrystals, but show strong effects on the slip deformation and fatigue cracking behavior. The microcracks were found to prefer to nucleate and propagate at the GB, leading to intergranular cracking. However, the crack nucleation behavior was found to be different for the above two iso-axial copper bicrystals. Two types of intergranular fatigue cracking mechanisms were proposed based on the specimen geometry with respect to the dominant slip system and the GB orientation.