"Micrograined" or "structural" superplasticity is the ability of policrystalline materials (metals, ceramics, composites) with very fine grain size (d<10 μm) to show high tensile elongations under low flow stresses, when deformed at high temperatures (T > 0.4 T m, where T m is the absolute melting point) and low strain rates (ε̇ = 10 -5 to 10 -1 s -1). The main microstructural requirements for the observation of superplastic behaviour in high strength materials (the aluminum alloys AA7012, AA7075 and AA7475, the precipitation hardening stainless steel 17- 4 PH [AISI 630] and the nickel-based superalloy IN- 718) are presented and discussed. The chemical compositions of the tested materials are reported in tables 1, 2, and 3, while the microstructures of the as-received alloys are shown in fig. 1. Taking into account the main deformation mechanism (grain boundary sliding), an important role is played not only by the presence of a fine-grained microstructure (stable at high deformation te...
Aspetti metallurgici nella superplasticità
GARAGNANI, Gian Luca
1997
Abstract
"Micrograined" or "structural" superplasticity is the ability of policrystalline materials (metals, ceramics, composites) with very fine grain size (d<10 μm) to show high tensile elongations under low flow stresses, when deformed at high temperatures (T > 0.4 T m, where T m is the absolute melting point) and low strain rates (ε̇ = 10 -5 to 10 -1 s -1). The main microstructural requirements for the observation of superplastic behaviour in high strength materials (the aluminum alloys AA7012, AA7075 and AA7475, the precipitation hardening stainless steel 17- 4 PH [AISI 630] and the nickel-based superalloy IN- 718) are presented and discussed. The chemical compositions of the tested materials are reported in tables 1, 2, and 3, while the microstructures of the as-received alloys are shown in fig. 1. Taking into account the main deformation mechanism (grain boundary sliding), an important role is played not only by the presence of a fine-grained microstructure (stable at high deformation te...I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
