Superplastic deformation in coarse-grained Fe-27Al alloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1998-12, Vol.258 (1-2), p.236-242
• Main Authors: CHU, J. P, LIU, I. M, WU, J. H, KAI, W, WANG, J. Y, INOUE, K
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Deformation and plasticity (including yield, ductility, and superplasticity); Exact sciences and technology; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Other heat and thermomechanical treatments; Physics; Treatment of materials and its effects on microstructure and properties
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(98)00939-3

The microstructure and high-temperature tensile properties of Fe-27Al (in at.%) alloy have been investigated. Tensile tests are performed in a temperature range of 600-800 deg C in air under an initial strain rate of 1x10 exp -4 s exp -1 . Important characteristics such as up to 300% elongation, strain-rate sensitivities of approx0.3 and low flow activation energy confirm that our Fe-27Al alloy with a coarse grain-size of approx700-800 mu m exhibits superplasticity at temperatures at or > 700 deg C. The low flow activation energy, approx250 kJ mol exp -1 , indicates the mechanism operating during the superplastic deformaiton is not likely controlled by the lattice diffusion. Our microstructural observations reveal several important features such as the low dislocation density, grain refinement, grain-boundary migration, cavity coalescence and grain-boundary cavity. The refined grain structure (approx100-200 mu m in size) is presumably attributed to the continuous grain-boundary migration, as evidenced by the presence of irregular curve-shaped grain boundaries. Interestingly, this strain-induced boundary migration might actually increase the surface energy, as opposed to the surface-tension-induced boundary migration that reduces the surface energy during a normal annealing process. Further studies are suggesteed in order to establish a better understanding of the mechanism for this grain-boundary migration and its roles on the superplasticity.