The mechanical behavior of a cryomilled Al–10Ti–2Cu alloy

Abstract

The mechanical behavior of a cryomilled Al–10Ti–2Cu (wt.%) alloy has been studied by performing uniaxial tension tests at temperatures ranging from room temperature to 525°C. Elastic–nearly perfectly plastic stress–strain behavior is observed at all temperatures. Tension–compression asymmetry of the room temperature yield stress is also observed. These characteristics are in agreement with those recently reported in the literature for single-phase NC materials. The flow stress (700 MPa at room temperature) decreases dramatically with increasing temperature. Testing of material following thermal exposures suggests that microstructural coarsening alone cannot account for the decrease in strength with increasing temperature. From a coarsening standpoint, this material appears to be very thermally stable. The ductility is influenced by several factors. Low levels of internal porosity along with the presence of fine oxide and carbide dispersoids contribute to lower ductility. The absence of work hardening exhibited by the Al–10Ti–2Cu also leads to reduced strain to failure. The features observed on fracture surfaces suggest that fracture occurs by the nucleation and growth of voids at particle–matrix interfaces. Evidence of fracture along prior powder particle boundaries is present as well. The microstructure consists primarily of regions containing grains measuring in the range 30–70 nm. Large grained regions consisting of nominally pure Al ranging in size from 300 to 500 nm are also present. No evidence of dislocation activity within either the fine or large grained regions can be found in the as extruded material. Specimens deformed at room temperature and 93°C reveal evidence of dislocation activity within the large grain regions. Dislocation configurations suggest an Orowan bypass mechanism. No dislocations are found within the 30–70 nm size grains following tensile deformation.