Significance of homologous temperature in softening behavior and grain size of pure metals processed by high-pressure torsion

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-09, Vol.528 (25-26), p.7514-7523
• Main Authors: Edalati, Kaveh, Horita, Zenji
• Format: Article
• Language: English
• Subjects: Aluminum; Cross-disciplinary physics: materials science; rheology; Deformation, plasticity, and creep; Exact sciences and technology; Grain size; Hardness; High-pressure torsion; Materials science; Microstructure; Physics; Severe plastic deformation; Softening; Stacking fault energy; Torsion; Treatment of materials and its effects on microstructure and properties; Ultrafine-grained materials; Zinc
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.06.080

► Metals with low melting points (In, Sn, Pb, Zn) were processed by high-pressure torsion (HPT). ► An unusual softening behavior was observed in these metals after processing by HPT. ► The hardness-strain behavior is represented by homologous temperature in HPTed metals. ► The steady-state grain size is significantly influenced by homologous temperature. ► The effect of stacking fault energy on grain size is minor at a given homologous temperature. High purity metals with low melting temperatures such as indium (99.999%), tin (99.9%), lead (99%), zinc (99.99%) and aluminum (99.99%) were processed using high-pressure torsion (HPT). An unusual softening behavior was observed in all these metals after processing by HPT at room temperature. Pure copper (99.99%) and palladium (99.95%) were used to simulate the softening behavior due to a thermal effect by processing and subsequently holding at the temperatures equivalent to room temperature of pure Al. It is shown that a hardness peak appears in any metal by static softening after processing by HPT at a homologous temperature of 0.32 which is equivalent to room temperature of pure Al. The contribution of dynamic softening on hardness decrease becomes more important as the homologous temperature and stacking fault energy increase. Microstructural examinations indicate that, although the stacking fault energy influences the rate of the microstructural evolution, the homologous temperature appears to be a dominant parameter to determine the steady-state grain size after processing by HPT.