In 1945, a short story by American sci-fi writer Murray Leinster described how a futuristic device “makes drawings in the air” out of plastic. More than half a century later, Leinster’s imagined device has come essentially to life through a technique we now call 3D printing.
3D printing has leapt out of the realm of science fiction and into standard industrial manufacturing practices, and even casual hobbyists can 3D sculpt and print their own creations at home. Difficult-to-print materials such as metals, however, require an alternative approach. In these cases, binder-jetting sprays blend powdered metals with binder particles made of cobalt before the mixture is heated to set the metal in the desired shape.
One of these base materials is an extremely hard metal called tungsten carbide (WC). The catch is that working with WC-cobalt blends is a serious occupational hazard. Zhengkai Xu, a research fellow at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech), explained that exposure to WC-cobalt materials leads to a chance of developing ‘hard metal lung disease’, a condition that has been linked to asthma, respiratory failure and even cancer.
In their study, Xu and colleagues explored a safer alternative—a binder made of nickel-chromium (Ni-Cr). This material is already widely used as an industrial coating to protect metal components from wear and tear.
The team’s investigation involved binder-jetting different WC-Ni-Cr parts and subjecting them to rigorous stress tests. They identified specific binder-jetting conditions where WC-Ni-Cr could be used to generate highly stable microstructures, improving the integrity of the final product. The researchers also found that Ni-Cr helped boost corrosion and wear resistance, creating metal parts that were significantly more resilient than those made using traditional cobalt binders.
While WC parts are currently manufactured by compressing tungsten carbide powder in a mould, this study opens up exciting design possibilities for 3D-printed WC parts. “We achieved over 98 percent density parts with good mechanical properties as well as corrosion and oxidation resistance,” said Xu, adding that these metrics should give manufacturers the confidence to swap their current protocols for binder jetting technologies.
Despite the promising performance, it will likely take a while before Ni-Cr becomes the new gold standard binder. “Using one material to replace another is a long process,” noted Xu. Meanwhile, the team plans to improve the physical properties of WC-Ni-Cr prints and further optimise the printing and heating process.
Still, Xu has high hopes for WC-Ni-Cr, noting that some manufacturers are already beginning to use this blend. “Although the replacement will not happen immediately, there are now more options out there for users,” Xu said.
The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology (SIMTech).