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Rapidly solidified nano-quasicrystalline Al 93 Fe 3 Cr 2 Ti 2 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 Al 93 Fe 3 Cr 2 Ti 2 at% alloy matrix, with the addition of 10 and 20 vol% 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. [ABSTRACT FROM AUTHOR]

We report a study of the structure-processing-property relationships in a high strength Al 93 Fe 3 Cr 2 Ti 2 nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to augment the ductility of the composites. [ABSTRACT FROM AUTHOR]

Nanoquasicrystalline Al-based alloys have been studied intensively for the last decade because of their promising mechanical properties. Recently quaternary nanoquasicrystalline alloys with improved thermal stability and better mechanical properties at elevated temperature have been reported. The present work describes an investigation into quaternary Al93Fe3Cr2Z2 (at.%) (with Z=Ti, V, Nb, Ta) and ternary Al93(Fe3Cr2)7, produced by melt spinning. Structural characterisation was carried out by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the thermal stability and decomposition of the quasicrystalline phase were studied by means of differential scanning calorimetry (DSC). All of the alloys showed a microstructure consisting of spherical icosahedral particles embedded in an α-Al matrix. The fourth component produced a significant refinement of icosahedral particle size. The decomposition of the quaternary alloys was observed at higher temperatures than for the ternary alloy with a broad exothermic peak. The new alloys containing Nb and Ta showed a multimodal transformation process extending up to the onset of melting. Icosahedral particles containing Ta or Nb were observed after heat treatment at 550 °C. [Copyright &y& Elsevier]

The microstructure, phase transformation and shape memory effect of the high temperature shape memory alloy Cu-11.4Al-3.2Ni-3Mn-0.5 Nb (wt%) were investigated for the first time. The shape recovery ratio can achieve 73% when submitted to 690 MPa and the compressive stress of fracture of the alloy is 1560 MPa. [ABSTRACT FROM AUTHOR]