Compressive mechanical properties of nanostructured intermetallic alloys Al₃Ti-X (X = Mn or Fe)

The mechanical behavior of the sintered nanostructured intermetallic alloys, Al₆₇Ti₂₅Mn₈ and Al₆₇Ti ₂₅Fe₈ has been investigated by means of compression tests as a function of temperature. These intermetallic materials are produced by mechanical alloying and spark plasma sintering. The sintered alloys have been characterized by X-Ray Diffraction and Transmission Electron Microscopy. Their nanostructure consists of a single-phase with an L1₂ (cubic) structure and an average grain size in the nanoscale (lower than 30 nm). These nanostructured intermetallics show considerably high ductility in compression at high temperature but are brittle at temperatures below 400°C. In such cases the compressive fracture strength can reach values as high as 1.8 GPa (Al ₆₇Ti₂₅Fe₈). At 500°C, some ductility is found together with a relatively high flow stress (around 1 GPa), the corresponding deformation curve shows strain hardening and in some cases stress serrations (strain aging). At 600°C, a low flow stress is measured (∼300 MPa) with high ductility. At 700 and 800°C, a quasi-superplastic behavior is found with a total deformation of around 45 and very low flow stresses. No evidence of dislocation motion is found at temperatures above 700°C suggesting a deformation mechanism based on grain boundary sliding.