Stored energy, vacancies and thermal stability of ultra-fine grained copper

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 492; no. 1; pp. 74 - 79
• Main Authors: Cao, W.Q., Gu, C.F., Pereloma, E.V., Davies, C.H.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25-09-2008; Elsevier
• Subjects: Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; ECAP; Exact sciences and technology; Materials science; Other heat and thermomechanical treatments; Physics; Recrystallization; Stored energy; Thermal stability; Treatment of materials and its effects on microstructure and properties; Vacancy; Vacancy; ECAP; Stored energy; Thermal stability; Recrystallization; Grain size; Stored energy,Vacancy,Thermal stability,Recrystallization,ECAP; Differential scanning calorimetry; Vacancies; Cold rolling; High angle boundary; Transition elements; Fine grain structure; Copper; Microstructure; Activation energy
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2008.02.048

The stored energy and thermal stability of oxygen-free high conductivity copper processed by equal channel angular pressing up to 16 passes at room temperature was studied by differential scanning calorimetry. Stored energy increased with strain up to four passes, after which it saturated at 0.95
±
0.05
J/g. This saturation value is 20% higher than from conventional cold rolling. The microstructure of the copper after eight passes was characterized by an average subgrain size of about 0.21
μm and high-angle boundary fraction of about 35%. The contributions to the stored energy from defects were calculated and compared, suggesting that the stored energy mainly originates from boundaries and vacancies. The restoration activation energy after eight passes was between 77 and 80
kJ/mol. The higher stored energy and lower activation energy compared to cold-rolled copper is attributed to excess vacancies.