Figure 48.

The central schematic presents an overview of the additive manufacturing process, whereby a directed energy source (laser or electron beam) melts a layer of metal powder (yellow), which solidifies (red to blue), fusing it to the previous (underlying) layer of metal (grey). (a) Conventional Al7075 powder feedstock. (b) Al7075 powder functionalized with nanoparticles. (c) Many alloys including Al7075 tend to solidify by columnar growth of dendrites, resulting in cracks due to solidification shrinkage. (d) Suitable nanoparticles can induce heterogeneous nucleation and facilitate equiaxed grain growth, thereby reducing the effect of solidification strain. (e) Many alloys exhibit intolerable microstructures with large grains and periodic cracks when 3D-printed using conventional approaches, as illustrated by the inverse pole figure. (f) Functionalizing the powder feedstock with nanoparticles produces fine equiaxed grain growth and eliminates hot cracking. (g) A 3D-printed, topologically optimized Al6061 piston on the build plate. (h) 3D-printed Al7075 HRL logo [185]. Copyright 2017. Adapted with permission from Springer Nature under the license number 4605280085008 (Figure 1 [185]), dated 7 April 2020.