Over the 2010s technological improvements allowed metal additive manufacturing to graduate from a prototyping tool to a widespread, full-scale manufacturing process. Among the capabilities still under development, however, is the ability to locally tailor alloy composition and properties to fabricate bulk, complex geometry functionally graded materials (FGMs), eliminating the need for dissimilar-metal welds and joints. The challenge of compositional grading involves overcoming chemical, metallurgical, and thermal property differences to achieve a continuous structure between a wide range of selected combinations of alloys. In this review, examples are discussed of fabricating FGMs joining a variety of combinations of stainless, nickel, titanium and copper alloys, and FGMs joining metals to ceramics and metal-matrix composites. The change in design strategy enabled by practical FGMs may lead to effective use of biomimetic designs that are both much more efficient as well as aesthetically pleasing.

Increasing demand for energy and reduction of carbon dioxide emissions has revived interest in nuclear energy. Designing materials for radiation environments necessitates a fundamental understanding of how radiation-induced defects alter mechanical properties. Ion beams create radiation damage efficiently without material activation, but their limited penetration depth requires small-scale testing. However, strength measurements of nanoscale irradiated specimens have not been previously performed. Here we show that yield strengths approaching macroscopic values are measured from irradiated ~400 nm-diameter copper specimens. Quantitative in situ nanocompression testing in a transmission electron microscope reveals that the strength of larger samples is controlled by dislocation–irradiation defect interactions, yielding size-independent strengths. Below ~400 nm, size-dependent strength results from dislocation source limitation. This transition length-scale should be universal, but depends on material and irradiation conditions. We conclude that for irradiated copper, and presumably related materials, nanoscale in situ testing can determine bulk-like yield strengths and simultaneously identify deformation mechanisms.