Abstract
Superplasticity is characterized by an elongation to failure of >300% and a measured strain rate sensitivity (SRS), close to 0.5. The superplastic flow is controlled by diffusion processes; it requires the testing temperature of 0.5Tm or greater where Tm is the absolute melting temperature of metals. It is well established that a reduction in grain size improves the optimum superplastic response by lowering the deformation temperature and/or raising the strain rate. The low-temperature superplasticity (LTSP) is attractive for commercial superplastic forming, in view of lowering energy requirement, increasing life for conventional or cheaper forming dies, improving the surface quality of structural components, inhibiting quick grain growth and solute-loss from the surface layers, thus resulting in better post-forming mechanical properties. This paper will summarize the dependence of superplasticity on grain size and shape in various metallic materials, including ferrous and non-ferrous alloys, which has been considered as an effective strategy to enable the LTSP.
Highlights
Superplasticity is the ability of metals to exhibit extremely large elongations of at least 300% prior to tensile failure, when deformation is imposed at relatively low strain rates (e.g., ε_ 10−3 to 10−5 s−1) and elevated temperatures (T > 0.5Tm), where Tm is the melting temperature of metals (Edington, 1982; Langdon, 1982)
Taking into account the grain size effect on high-temperature deformation, a model on superplastic deformation was proposed by Lou and Woo (2002), based on the theory of GBS and the theory of cavity growth, as follows: FIGURE 3 | Total elongation against inverse grain size for several superplastic materials. + Ti-6Al-4V deformed at 1200 K and 2.0 × 10−4 s−1; Ternary brass deformed at 874 K and 1.67 × 10−4 s−1; 7475 Al alloy deformed at 789 K and 3.0 × 10−4 s−1; × Al-Mg-Sc alloy deformed at 698 K and 3.0
This work summarized the dependence of superplasticity of various metals on grain size and shape, including Al alloy, Ti alloy and ferrous alloy, etc
Summary
Role of Grain Size and Shape in Superplasticity of Metals. Superplasticity is characterized by an elongation to failure of >300% and a measured strain rate sensitivity (SRS), close to 0.5. It is well established that a reduction in grain size improves the optimum superplastic response by lowering the deformation temperature and/or raising the strain rate. The low-temperature superplasticity (LTSP) is attractive for commercial superplastic forming, in view of lowering energy requirement, increasing life for conventional or cheaper forming dies, improving the surface quality of structural components, inhibiting quick grain growth and solute-loss from the surface layers, resulting in better post-forming mechanical properties. This paper will summarize the dependence of superplasticity on grain size and shape in various metallic materials, including ferrous and non-ferrous alloys, which has been considered as an effective strategy to enable the LTSP
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