Most mechanisms used for strengthening crystalline materials lead to the reduction of ductility. Selective laser melting produces a stainless steel with both significantly enhanced strength and ductility. 3D-printed part for nuclear fusion test reactor. Courtesy of Leifeng Liu, University of Birmingham. A joint research team from the University of Birmingham, Stockholm University, and Zhejiang University in China developed the technique to 3D-print metals — involving a widely used stainless steel — and achieved exceptional levels of both strength and ductility when compared to counterparts from more conventional processes. The research counters skepticism about the ability to make strong and ductile metals through 3D printing, so the discovery is crucial to moving the technology forward for the manufacturing of heavy-duty parts. "Strength and ductility are natural enemies of one another — most methods developed to strengthen metals consequently reduce ductility," said University of Birmingham researcher Leifeng Liu. “The 3D printing technique is known to produce objects with previously inaccessible shapes, and our work shows that it also provides the possibility to produce the next generation of structural alloys with significant improvements in both strength and ductility." This has been made possible thanks to the ultrafast cooling rate, estimated to range from 1000 °C per second to 100 million °C per second — something that was not possible in bulk metal production processes until the emergence of 3D printing. The researchers found that the improved mechanical properties can be attributed to the cooling down of the metal to a so-called nonequilibrium state. "This work gives researchers a brand new tool to design new alloy systems with ultramechanical properties,” said Liu. “It also helps metal 3D printing to gain access into the field where high mechanical properties are required, like structural parts in aerospace and automotive industry." 3D printing has long been recognized as a technology that can potentially change manufacturing, allowing the rapid production of objects with complex and customized geometries. With the accelerating development of the technology in recent years, 3D printing, especially metal 3D printing, is quickly progressing toward widespread industrial application. The research has been published in the journal Materials Today (doi.org/10.1016/j.mattod.2017.11.004).