There are many potential benefits to using additive manufacturing — also known as 3D printing — for making metal parts, rather than conventional manufacturing processes. For example, additive manufacturing is highly customizable, it can produce complex structures and it can be used for the economical production of low numbers of metal components. But to achieve the strict specifications needed for some applications, the microscopic structure of printed metal objects must be controlled. Writing in Nature, Zhang et al.1 describe titanium–copper alloys that produce practically useful microscopic structures during additive manufacturing, removing the need for subsequent treatment. The resulting materials exhibit promising combinations of mechanical properties, comparable to those of the ubiquitous structural alloy Ti-6Al-4V, produced using conventional and additive manufacturing processes.
In metal additive manufacturing, an alloy (in the form of powders or wires) is deposited in a layer and then melted by a rapidly moving heat source to form a solid mass; successive layers are built up to produce a 3D part. The process typically produces large temperature gradients, high solidification rates and repeated cycles of heating and cooling. A common characteristic of 3D-printed metals is coarse columnar grains that grow along specific directions of the crystal lattice that are favourably oriented with the heat flow (Fig. 1a).
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