Effect of Grain Size of Cu-Zn Alloys on Dislocation-Strengthening Factors

Relationship between dislocation multiplication and work hardening of tensile deformed Cu-Zn alloys with different grain sizes was investigated. X-ray diffraction line-profile analysis was employed to evaluate dislocation parameters. It was confirmed that dislocation multiplication was enhanced with a decrease in the grain sizes. This was mainly caused by GN (Geometrically Necessary) dislocation, which was characterized by KAM (Kernel Average Misorientation) in EBSD (Electron Back Scatter Diffraction). The strength of dislocation hardening was evaluated from the a value in the Bailey-Hirsch equation: sigma = sigma(0) + M-T alpha Gb root rho.The alpha values were estimated by plotting the flow stress against square root of dislocation density. The a values became smaller with the decrease in the grain sizes, suggesting that the strength of dislocations hardening for unit length of dislocation became smaller. In order to elucidate the origin of the relationship between the grain size and the a values, the influence of grain size on the fraction of GN dislocation density as well as the outer radius of dislocation strain field. Whereas the effect of the fraction of the GN dislocation on the a values was small, the outer radius of dislocation strain field strongly affected the alpha values.