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Quasicrystalline aluminium alloys and aluminium based nanocomposites with the advantage of high strength over commercial aluminium alloys have been studied for many years. In this work a nanoquasicrystalline Al-Fe-Cr-Ti alloy powder and a nanocomposite consisting of a mixture of a nanoquasicrystalline alloy and nanosize γ-Al 2 O 3 powders were produced through mechanical milling with different milling speeds. It has been observed that a higher milling time or milling speed can improve the homogeneity of the γ-Al 2 O 3 distribution. The α-Al crystallite size decreases and the hardness increases with the milling time. The smallest crystallite size (14 nm) and the highest hardness value (638 HV 10g ) were obtained for the nanocomposite after 30 h of milling at 250 rpm. As the α-Al crystallite size is the main change in the microstructure during the ball milling process, the change in the hardness of the milled powders was found to follow a Hall-Petch type relation with an exponent of 0.25. [ABSTRACT FROM AUTHOR]

Highlights: [•] The feasibility to produce nanoquasicrystalline Al–Fe–Cr–Nb bars was investigated. [•] Refined microstructures were obtained for a melt atomization temperature >1250°C. [•] Icosahedral particles were obtained in atomized powder sizes under 75μm. [•] Large fraction of icosahedral particles can be retained in bars extruded at 375°C. [•] Nanoquasicrystalline bars showed high ability to retain high strength at 250°C. [ABSTRACT FROM AUTHOR]

Quasicrystalline aluminium alloys have been studied in the past years achieving higher strength than commercial Al alloys and retaining high strength at high temperature. In this work a quasicrystalline Al alloy matrix nanocomposite containing nanoceramic particles has been manufactured using ball milling and hot extrusion. For that purpose a nanoquasicrystalline Al–Fe–Cr–Ti alloy was manufactured by powder atomisation. Nanocomposites consisting of a quasicrystalline Al–Fe–Cr–Ti alloy matrix and reinforcement of γ-Al 2 O 3 nano particles were manufactured. The effect of ball milling time on the microstructure and microhardness of the nanocomposite powders was investigated. Bulk materials were produced by consolidation and hot extrusion. The microstructure and microhardness of the extruded materials were characterised. The milling regime behaviour is discussed, and shows three different steps that have a significant effect on the rate of change of uniformity of the reinforcement distribution, matrix microstructure, powder size distribution and its microhardness. No significant decomposition of the quasicrystalline phase occurred over 30 h of milling. Strain increased and the crystallite size of the aluminium phase decreased with milling time, with the Al crystallite size reaching a steady state. Although the quasicrystalline phase decomposed during hot extrusion, the microhardness of the nanocomposite produced is significantly harder (227 ± 3 μHV 500 ) than both the unreinforced quasicrystalline alloy (159 ± 1 μHV 500 ) and crystalline aluminium nanocomposites reported in the literature [1] . Methods and analysis of material behaviour put forward in this work inform further understanding and optimisation of this and other nanocomposite systems containing a metastable microstructure matrix. [ABSTRACT FROM AUTHOR]

The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new and high performance lightweight materials. The development of nanostructured Al-based alloys and composites is a key direction towards solving this demand. High energy prices and decreased availability of some alloying elements open up the opportunity to use non-conventional elements in Al alloys and composites. In this work the application of Nb in rapid solidified Al-based alloys and Al alloys matrix composites is reviewed. New results that clarify the effect of Nb on rapid solidified Al alloys and composites are also presented. It is observed that Nb stabilises the icosahedral Al–Fe/Cr clusters, enhances the glass forming ability and shifts the icosahedral phase decomposition towards higher temperatures. Nb provides higher corrosion resistance with respect to the pure Al and Al–Fe–RE (RE: rare earth) alloys in the amorphous and crystalline states. The use of Nb as a reinforcement to produce new Al alloy matrix composites is explored. It is observed that Nb provides higher strength, ductility and toughness to the nanoquasicrystalline matrix composite. Nb appears as a new key element that can improve several properties in rapid solidified Al alloys and composites. [ABSTRACT FROM AUTHOR]

Highlights: [•] We evaluated the influence of the spray forming in the microstructure. [•] Refined microstructure with low level of segregation was obtained. [•] It were provided good mechanical properties at the end stage of the processing. [•] The artificial aging provided a fine nanosized distribution of η′ precipitates. [•] Spray forming showed to be a promissory route to reprocess 7000 Al alloys. [ABSTRACT FROM AUTHOR]

The behaviour of the martensitic phase transformation of a Cu-Al-Ni-Mn shape memory alloy was studied for as-atomized and heat-treated powders. X-ray diffraction, microscopy techniques and thermodynamic calculations were used to understand the different transformation behaviour observed during differential scanning calorimetry (DSC) analysis. Two overlapped transformation peaks were observed in the DSC curves for the as-atomized powder. After annealing, the peaks progressively became only single peak when the annealing temperature and time were increased. No difference in phase formation and microstructure was observed by X-ray diffraction and scanning electron microscopy when compared as-atomized and annealed powders, although transmission electron microscopy analyses showed that the as-cast powders had more dislocations trapped in the microstructure than the annealed samples. Considering the experimental results and thermodynamic considerations, it was concluded that the smooth double peak effect in the as-atomized powders occurred due to a different state of internal stresses and elastic energy accumulation during forward transformation. The absence of this effect after heat treatment shows that the internal stresses and defects were annihilated after annealing, changing the elastic energy accumulation and the transformation behaviour. Understanding the martensitic transformation on Cu-Al-Ni-Mn powders is important considering the potential use of powder metallurgy processing route. [ABSTRACT FROM AUTHOR]

Materials with high specific strengths as well as damage tolerance are of great importance for automotive and aerospace applications. Ceramic reinforced metal matrix composites (MMCs) show good potential for these uses but have been hampered by insufficient ductility and production issues, both of which this work looks to resolve. Nanoparticle reinforced 6061 aluminium alloy matrix composites have been produced by a powder metallurgy route and shown to exhibit high strength and Young’s modulus alongside good ductility and low density. A powder metallurgy route consisting of high energy ball milling, hot isostatic pressing (HIP) and extrusion has proved a highly effective process for achieving a homogeneous distribution of particles, with minimal clustering of the nanoparticles, at an industrially relevant scale. After heat treatment the composites display high strengths, owing to SiC nanoparticle reinforcement as well as the age hardening effect. The remarkable feature of nanoparticle reinforced MMCs compared to micron size reinforcements is that particle fracture does not occur and effective particle–matrix bonding can be taking place, resulting in a greater combination of strength and toughness. The combination of properties achieved by the composites studied in this work are superior to most of the micron sized particle reinforced MMCs reported elsewhere and are well beyond what is possible with traditional aluminium alloys. [ABSTRACT FROM AUTHOR]