Elevated temperature mechanical behaviour of nanoquasicrystalline Al93Fe3Cr2Ti2 alloy and composites

Abstract

Rapidly solidified nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy has previously shown outstanding tensile and compressive strength and microstructural stability up to elevated temperatures. Despite this, no study had previously assessed the effect of plastic deformation at elevated temperature to simulate thermal-mechanical forging processes for the production of engineering components. The present work analysed bars consisting of a nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy matrix, with the addition of 10 and 20vol% pure Al ductilising fibres, produced through gas atomisation and warm extrusion. The microstructure was made primarily of nanometre-sized icosahedral particles in an α-Al matrix. Compression tests were performed across a range of temperatures and strain rates. The measured yield strength at 350°C was over 3x that of “high strength” 7075 T6 Al alloy, showing outstanding thermal stability and mechanical performance. However, the microstructure was shown by XRD to undergo a phase transformation which resulted in the decomposition of the icosahedral phase around ~500°C into more stable intermetallic phases. Serrated flow associated with dynamic strain ageing was observed and a semi-quantitative analysis matching elemental diffusion speeds with dislocation speed at specific strain rates was performed, which tentatively identified Ti as the solute species responsible within the selected range of temperatures and strain rates.