Dec 11, 2017 | By Benedict

A joint research team from the UK, Sweden, and China has developed a new stainless steel SLM 3D printing technique that results in high levels of strength and ductility. The process could be used to make heavy-duty parts for the aerospace and automotive sectors.

While users of plastic 3D printers have found plenty of success printing rubbery and stretchy objects using flexible 3D printer filaments, achieving ductility in the metal 3D printing world has proven rather more difficult.

The general outlook seems to be that one can’t additively manufacture a metal part that has high levels of both strength and ductility, since one trait normally compromises the other. Strong 3D printed metal parts therefore tend to be rigid and brittle—fine for many applications, but not for all.

But sometimes the key to unlocking a breakthrough is collaboration, and researchers from three universities across the world—the University of Birmingham, UK; Stockholm University, Sweden; and Zhejiang University, China—recently came together to develop a new metal 3D printing process that overcomes the additive manufacturing strength-ductility bottleneck.

Their new Selective Laser Melting (SLM) technique, which also enables the printing of “previously inaccessible shapes,” offers an ultrafast cooling rate—1000°C per second to 100 million °C per second—which leads to some highly desirable mechanical results, which could make 3D printed stainless steels a more attractive proposition to manufacturers of cars and aircraft, amongst other things.

The technique's rapid cooling rate, which could not have been achieved with a metal production process besides additive manufacturing, puts the metal into a non-equilibrium state. This can produce microstructures like a sub-micro-sized dislocation network, which in turn results in desirable mechanical properties like strength and ductility.

Ultimately, this dislocation network means greater flexibility for engineers who need complex metal shapes that aren’t necessarily rigid or brittle.

"This work gives researchers a brand new tool to design new alloy systems with ultra-mechanical properties,” says Dr. Leifeng Liu, lead author, who recently moved to the University of Birmingham from Stockholm University as an AMCASH research fellow. “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.”

Liu’s University of Birmingham team—Dr. Yu-Lung Chiu, Dr. Ji Zou, and Dr. Jing Wu, all of whom are part of the university’s School of Metallurgy and Materials—were responsible for establishing a micro and nano material testing system inside electron microscopes, allowing the researchers to analyze the performance of the 3D printed metal sample during mechanical tests.

This testing system reportedly helped the researchers understand the physical mechanisms at play, and to identify effective microstructural features of the printed metals.

The researchers’ study, “Dislocation network in additive manufactured steel breaks strength–ductility trade-off,” has been published in Materials Today.



Posted in 3D Printing Technology



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Mike K wrote at 12/11/2017 4:30:37 PM:

This is not true, strong and ductile parts have been fabricated by SLM for many years. The process inherently provides a very high cooling rate.

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