Effects of stacking fault energy on the thermal stability and mechanical properties of nanostructured Cu-Al alloys durin
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Effects of stacking fault energy (SFE) on the thermal stability and mechanical properties of nanostructured (NS) Cu–Al alloys during thermal annealing were investigated in this study. Compared with NS Cu–5at.%Al alloy with the higher SFE, NS Cu–8at.%Al alloy exhibits the lower critical temperatures for the initiation of recrystallization and the transition from recovery-dominated to recrystallization-dominated process, which significantly signals its low thermal stability. This may be attributed to the large microstructural heterogeneities resulting from severe plastic deformation. With increasing the annealing temperatures, both Cu–Al alloys present the similar trend of decreased strength and improved ductility. Meanwhile, the remarkable enhancement of uniform elongation is achieved when the volume fraction of Static recrystallization (SRX) grains exceeds ~80%. Moreover, the better strength–ductility combination was achieved in the Cu–8at.%Al alloy with lower SFE. I. INTRODUCTION
Nanostructured (NS) and ultrafine-grained (UFG) materials have recently received considerable attention because of their extraordinarily high strength and hardness compared with that of their counterparts.1,2 Disappointingly, the introduction of profuse artifacts and saturation of defects during preparation deteriorates their ability to accumulate dislocations, which results in the inadequate ductility of these high-strength materials. This shortcoming has become an essential bottleneck keeping them far from practical utility.3 Of several strategies proposed to improve their ductility,4–8 an appropriate thermal annealing treatment can conveniently and effectively optimize the mechanical properties of NS/UFG metals.5,6 A superior combination of high strength and good ductility is achieved in the NS/UFG metals with a “bimodal” microstructure (NS matrix grains and micrometer-sized recrystallized grains) induced by thermal annealing. Thus, this toughening strategy has been used to experimentally improve the mechanical properties of NS/UFG metals with different crystallographic structures including face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystals.6,8–11 In these close-packed structures, stacking fault energy (SFE) plays crucial roles in the microstructures and mechanical behaviors during not only plastic deformation but also thermal annealing in metallic materials.12–14 Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2010.39 J. Mater. Res., Vol. 26, No. 3, Feb 14, 2011
Recently, bulk NS Cu–Al alloys with different SFEs were synthesized using equal channel angular pressing (ECAP), and the grain refinement mechanism, microstructures, and mechanical properties are markedly influenced by tailoring the SFE of the Cu–Al alloys.15–18 Although the overall mechanical properties were improved with decreasing the SFE of alloys, the uniform elongation was still limited. Therefore, the purpose of the present study is to apply a thermal annealin
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