Cracks of Cu-Cr-Zr Alloy Bars under Planetary Rolling

The paper investigated grain sizes and cracks between the edge and the center of Cu-Cr-Zr alloy bar through macrostructure and microstructure. A crack in the center was explored by images of transverse and longitudinal sections with scanning electron microscope (SEM). Results show that the grain size in the edge is obviously finer than that in the center as completely dynamic recrystallization occurs easily; the microcrack of about 40 μm is formed in the center by second phase particles. Some bcc type precipitates Cr and intermetallics such as Cu51Zr14 and Cu5Zr are the source of microcracks initiation owing to coarse grains decreasing the strength. Therefore, refining of grains in the center is necessary to prevent microcracks. The formation mechanism of cracks can be explained by a dislocation model of microporosity nucleating, growing and polymerizing (MNGP).