Annealing behavior and mechamical property in pure copper processed by equal channel angular extrusion and cryo-rolling
| Autor: | Chia-Hao Yang, 楊家豪 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Ultrafine-grained (UFG) and nanocrystalline (NC) metals usually have higher strength than the coarse-grained counterpart but also exhibit low tensile ductility at room temperature. Recently, much attention has been drawn to improve the tensile ductility in the UFG/NC metals. In this study, pure copper (99.99%) was processed by equal channel angular extrusion (ECAE) and cryo-rolling to a rolling reduction of 95%. The as-deformed sample was then annealed at various temperatures ranging from 100oC to 320oC for 1 hour. The mechanical properties and microstructure of the as-deformed and isochronally annealed samples were investigated. to study the mechanical and annealing behavior of the NC copper. Low stacking fault energy (SFE) copper facilitates twin formation. Twins and/or stacking faults can hinder dislocation slip and increase dislocation accumulation and consequently increase work hardening rate and enhance tensile ductility. The yield stress (YS) is increased to 510MPa and the total tensile elongation is 6.1% in the as-deformed copper. The as-deformed microstructure appears to be lamellar structure and dislocation density within the grain interior is high. The annealed samples show that the average boundary spacing increases with increasing annealing temperature. When the NC copper was annealed at temperature below 200oC, the boundary spacing followd a stable growth rate and exhibits continuous recrystallization phenomenon, When the annealing temperature is above 200oC, the average boundary spacing increased dramatically and shows discontinuous recrystallization phenomenon. Samples annealed at 200oC for 30 minutes and 160oC for 5 hours appear to have better mechanical properties (higher strength and ductility combination) than other samples. However, the ductility of the NC copper is still fairly limited in the present work. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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