3D printing, or additive manufacturing, of metals uses a direct energy source, such as a laser or electron beam, to alloy powders, but has succeeded for only a few metals. Often, large columnar grains and cracks are generated during the solidification stage. In this paper, John Martin et al. confront this problem for aerospace-grade aluminium alloys that could not previously be 3D-printed. They decorate the metal powder feedstock with grain-refining nanoparticles that target each alloy. The composition of these nanoparticles was computed by identifying matching crystallographic lattice spacing and density to provide a low-energy nucleation barrier. During solidification, these nucleants generated small equiaxed grains which more easily accommodated the stresses generated during solidification, reducing the likelihood of cracks forming. The mechanical properties of the resulting structures were superior to those achieved without the grain refiners and comparable to those of wrought metal.
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