Superplasticity of fine-grained ceramics and intermetallics

Abstract

The tensile elongation of fine-grained ceramics is shown to increase as a strong function of decreasing flow stress, even though the values of strain-rate-sensitivity exponent remain high. The tensile ductility dependence on grain size was also investigated for many fine-grained ceramics either under a constant strain rate condition or a constant stress condition. The large increase of tensile ductility with the decrease of grain size under a constant strain rate, is primarily attributed to the decrease in flow stress accompanying grain size refinement. Tensile elongation behavior of some fine-grained intermetallic alloys appears similar to that typically observed in fine-grained ceramics, indicating similar failure mechanism shared by both materials.

Mechanical Alloys in the Al-Rich Part of the Al-Ti Binary System

“…Re-equilibration of this material was shown by thermal analysis to result in the formation of the L1 2 (at 365 °C), D0 23 (at 454 °C) and D0 22 (at 637 °C) phases [10]. A preliminary study investigating mechanical alloys in the Al-Al 3 Ti compositional range and limited to temperatures below 600 °C, essentially confirmed this transformation sequence for all compositions [11]. In order to relate the re-equilibration processes in mechanical alloys to ignition and combustion behavior, their total energetic destabilization must be characterized, and the relaxation process must be described until equilibrium is achieved.…”