Quasicrystal-reinforced aluminum metal matrix composites exhibit combinations of properties that are attractive for metal additive manufacturing. It is challenging to evaluate such systems due to ...difficulties in modeling the solidification and microstructural evolution. Here, laser glazing in a powder bed fusion instrument was used as an efficient method to evaluate an Al85Cu6Fe3Cr6 alloy, and the resulting microstructures were characterized using electron microscopy. The arc-melted alloy contained only crystalline phases, but pre-glazing of the surface gave a refined microstructure comprising I-phase quasicrystals, Al2Cu and FCC Al. Individual laser tracks produced in this layer under different conditions exhibited an extremely fine and uniform phase mixture with over 70% by volume of I-phase in a FCC Al matrix with a thin film of Al2Cu at the interface, and no cracking or macrosegregation. The reasons for the formation of I-phase, rather than the D-phase that has been reported previously in this alloy, are discussed.
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Using first-principles computations we provide comprehensive energetics at zero Kelvin of Guinier-Preston zone (GPZ) formation and topologies of GPZs in two classical Al binaries: Al-Cu and Al-Ag. ...Without a priori geometric and morphological assumptions, we conclusively show that GPZs in Al-Cu prefer a planar arrangement of {100} layers while GPZs in Al-Ag consist of clusters with {111} facets. We expand the model to 34 additional elements from the fourth and the fifth rows of the periodic table. The morphologies can be entirely related to directional nature and hybridization of Al 3s and 3p orbitals in the presence of secondary elements.
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One advance is the discovery that, with certain multicomponent alloys involving zirconium-, iron-, and magnesium-base systems, it is possible to achieve the amorphous state in bulk volumes during ...slow cooling of the liquid or during intense deformation of layered component assemblies. The second development concerns a growing number of alloys, including aluminum-- base and iron-base alloy systems, that can be processed as glasses by rapid liquid quenching.
Al-Ce and Al-Co binary alloys with compositions of 0.5, 1.0, and 3.0 at.% were arc-melted, allowed to solidify, and then characterized by a combination of X-ray diffraction and electron microscopy ...techniques. In case of the Al-Ce system, α-Al and Al11Ce3 phases were observed for all three compositions. The 0.5% and 1.0 at.% Al-Ce alloy microstructures contain pro-eutectic α-Al and a α-Al/Al11Ce3 eutectic, whereas the 3 at.% Al-Ce alloy is fully eutectic. These eutectics are lamellar in each case. The Al-Co system reveals pro-eutectic α-Al phase and an Al/Al9Co2 eutectic for the 0.5 at.% composition, a largely eutectic microstructure for the 1 at.% alloy, and dendrites of the Al9Co2 phase, surrounded by a sheath of α-Al, with pockets of eutectic between these features for the 3 at.% composition. For the 0.5 at.% and 1 at.% Al-Co alloys the eutectic is rod-like. The orientation relationships between the intermetallic and α-Al phase were determined for the eutectics using electron diffraction, and the morphology was related to the interfacial lattice matching between the phases.
•Both AlCe and AlCo alloys exhibit characteristic eutectic microconstituents.•In AlCe the Al/Al11Ce3 eutectic is lamellar with pronounced interfacial facets.•Facets correspond to planes of low interfacial misfit between the two structures.•In AlCo the Al/Al9Co2 eutectic is rod-like with no interfacial facets.•Many low misfit planes about the rod axis giving less anisotropic interface energy.
Two-dimensional (2D) dynamic image analysis (DIA) is often used to measure particle size and shape distributions of metal powders in terms of various size and shape parameters. In this present work, ...five titanium alloy (Ti–6Al–4V or Ti64) powders that were previously characterized with DIA are now characterized in three dimensions (3D) using a combination of X-ray computed tomography (XCT) and mathematical analysis, with various size and shape parameters, including porosity, measured and calculated for each particle. Measured 3D XCT-measured parameters are compared to 2D DIA-measured parameters. The 3D characterization was also used to mathematically generate 2D projection data, with particle orientation averaged over many directions, so that comparisons could be directly made to the previous DIA measurements. The 3D characterization is used to clearly see differences between the powders, including internal porosity and the percentage of single near-spherical particles (SnS) and non-spherical (NS) particles (mostly multi-particles) in each powder. In addition, the 3D data was used to generate 2D projections that were oriented along different directions, which was employed to show that the DIA instrument generated particle projections that were partially oriented along different dimensions of the particles. This partial orientation was apparent in the 2D particle shape data, not the particle size data. All these results show that current powder standards, which all five powders met, are inadequate to completely characterize powder size and shape parameters that could be important in a metal additive manufacturing process.
In structural applications bulk metallic glasses are almost inevitably exposed to repeated elastic loading and unloading. This communication highlights changes in the thermomechanical and ...calorimetric behavior of a Cu50Hf41.5Al8.5 bulk metallic glass with cyclic elastic deformation. The calorimetric analysis shows a stabilization of the amorphous phase with cyclic deformation at room temperature. The thermomechanical behavior of the metallic glass following the cyclic elastic deformation resembles the effect of annealing. The results demonstrate that a repeated elastic deformation can affect the phase stability of metallic glasses.
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