3D printing is revolutionizing many areas of manufacturing and science. In particular, 3-D printing of metals has found novel applications in fields as diverse as customized medical implants, jet engine bearings and rapid prototyping for the automotive industry. While many techniques can be used for 3-D printing with metals, most rely on computer-controlled melting or sintering of a metal alloy powder by a laser or electron beam. The mechanical properties of parts produced by this method have been well studied, but not enough attention has focused on their electrical properties.

Now in a paper appearing this week on the cover of the journal Applied Physics Letters, from AIP Publishing, a team of University of Melbourne and University of Western Australia researchers report creating a resonant microwave cavity that they 3-D printed via an aluminum-silicon alloy (Al-12Si). It exhibits superconductivity when cooled below the critical temperature of aluminum (1.2 Kelvin). 

"Conductivity is a measure of how easily an electrical current flows through a material, while 'superconductivity' is this measure taken to its extreme," explained Professor Michael Tobar, University of Western Australia node director of the Center for Engineered Quantum Systems. "It's an effect observed within a number of materials, characterized by the complete vanishing of any resistance to the flow of electrical current when cooled below a certain temperature."

Superconducting cavities are useful for numerous areas of physics -- from quantum physics to particle accelerators. But designing superconducting cavities is becoming more complex, often involving nonstandard geometries and arrays of resonators, which makes conventional machining more challenging. 

So two groups at the University of Western Australia -- one led by Professor Tim Sercombe, an expert in materials and 3-D printing, and the other led by Tobar, an expert in engineered quantum systems and novel cavity designs -- combined their expertise and launched a pilot study to explore the superconducting properties of 3-D printed parts. 

"The physics of superconductivity is well understood, and it has been known for decades that aluminum exhibits superconductivity," Tobar said. "But the 3-D printing process relies on aluminum that's far from pure and it undergoes several processes -- atomization, laser melting, furnace annealing, etc. So we wanted to explore whether a range of known superconducting metals could successfully be 3-D printed and retain their desirable electrical property."