Characteristic fatigue damage near the Σ3(111) coherent twin boundary in micron-sized copper specimen

Abstract

To investigate the effect of a Σ3(111) coherent twin boundary on the fatigue damage of micron-sized Cu, a tension–compression cyclic-deformation test was performed on a bicrystal specimen. The fatigue damage (extrusion/intrusion) occurred preferentially around the twin boundary, induced by stress concentration on one side of the specimen due to the deformation constraint between the crystals. Even though stress relaxation occurred on the opposite side, the fatigue damage along the twin boundary penetrated the specimen. The shapes of the extrusion and intrusion of the opposing sides were coincident, and the dislocation density in the damaged region was lower than that in the far region. These results indicate that the dislocations generated at the stress-concentration sites overcame the stress-relaxation effects and traveled along the twin boundary to escape from the opposite side because of the close distance between the surfaces in the specimen. The ease of dislocation ejection promoted the formation of extrusion/intrusion and decreased the fatigue strength of the specimen. The findings will facilitate the development of materials with improved resistance to fatigue damage.