Researchers from Skoltech — a VEB.RF group institution — and their colleagues from State Marine Technical University and elsewhere have found a way to improve the balance between the mechanical strength and ductility of 3D-printed aluminum bronze. An alloy of copper and aluminum with a minor addition of iron, this material is a promising candidate for making additively manufactured heat exchange units that cool sensitive electronic components, such as processors. When these components have to operate under extreme conditions on aircraft, rockets, and electric cars, optimizing the strength and ductility of the constituent materials becomes a major concern. The study came out in the Journal of Alloys and Compounds.
“The heat exchanger is a unit in electronics that moves heat away from the processor or other heat-generating components. To do its job well, it has to be made of a material with a high thermal conductivity and has to have the right geometry,” says the study’s lead author, Anastasia Filippova, a PhD student in Skoltech’s Mathematics and Mechanics program. “While 3D-printed aluminum bronze offers a good combination of thermal properties and control over geometry, suboptimal mechanical characteristics may result from the printing process. This is a concern particularly in electronics used in rockets and other vehicles subjected to shock, vibration, and repeated thermal and mechanical loading.”
Pure copper provides exceptional thermal conductivity, but for that very reason — as well as due to its high reflectivity — it is difficult to process using conventional infrared laser 3D printing techniques. Besides this, the high plasticity of copper makes thin parts made of that metal prone to deformation under mechanical loads. Alloying copper with 10% aluminum and 1% iron allows both issues to be addressed, but there’s a catch: reduction of thermal conductivity. The rapid solidification during printing can produce local compositional variations and a nonequilibrium phase structure. These microstructural features can affect the strength and ductility of the printed alloy.
After observing the tell-tale nonequilibrium microstructural regions in aluminum bronze samples obtained by 3D printing with a scanning electron microscope, the team hypothesized that heat treatment — a standard postprocessing approach — might resolve the inhomogeneity problem.
“However, 3D-printed materials are always somewhat different in terms of their microstructure, compared with the same alloy processed by other techniques. This means that a conventional postprocessing method like heat treatment will not necessarily work. In fact, it might even make the properties worse. And it may require fine-tuning in terms of heating parameters, which is how it turned out to be,” says the principal investigator of the study, Associate Professor Stanislav Evlashin from the Center for Materials Technologies at Skoltech.
