Reaction of Sn to Nanocrystalline Surface Layer of Cu by Near Surface Severe Plastic Deformation

Abstract

The near surface ultrafine grains (NSUFG) layer with grain sizes of about 35nm to 200nm from surface to about 10 μm was prepared in the OFHC-Cu sheet with coarse grains size of about 7.2 μ m (CG-Cu) by Near Surface Sever Plastic Deformation method. The solid reactions of Sn to NSUFG layer and CG-Cu were basically investigated at 379K to 493K for 1x10 3 to 6x10 6 s. The Cu 6 Sn 5 (η) and Cu 3 Sn (e) layers were formed between Cu and Sn. The thickness of the e layer in NSUFG-Cu/Sn was similar to that in CG-Cu/Sn one, while the thickness of the η layer in NSUFG-Cu/Sn reaction was about two times thicker than that in CG-Cu/Sn one. This enhancement of the η layer growth in NSUFG-Cu/Sn reaction was due to the large supply of Cu atoms to the reaction layer by the grain boundary diffusion in the NSUFG-Cu. The rate-controlling processes of layer growth were boundary diffusion mechanism in reaction layer at lower temperatures in shorter annealing time, and volume diffusion mechanism at higher temperatures in longer annealing times.