Additive Manufacturing

JUL 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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Page 34 of 60

JULY 2018 Additive Manufacturing FEATURE / Metal Additive Manufacturing 32 order to deliver additional benefits," Herbert says. The company's recently launched CarTech Puris 5+ titanium alloy is an example of this sort of tweaking. This material grew out of the difficulty that CalRam (before its acquisition) was experiencing in 3D printing with Grade 5 titanium alloy (Ti-6Al- 4V), says Eric Bono, manager of Carpenter Technology's Additive Manufacturing Group. "They could not meet required mechan- ical properties with adequate ductility, and they came to us to solve the problem," he explains. While Ti-6Al-4V is widely used, Bono says, the material itself has some issues when paired with AM. Namely, oxygen. Per ASTM International standards, Grade 5 titanium can contain no more than 0.2 percent oxygen. However, each time titanium powder is used and recycled, the oxygen content increases. Stan- dard Grade 5 titanium powder used in critical applications has a starting oxygen content of approximately 0.17 percent, which doesn't leave much leeway for reuse. CalRam's application challenged Carpenter to create a low-oxygen titanium allow to facilitate more recycling, reduce overall cost, and provide a better guarantee of part quality. But it wasn't just a simple matter of reducing the oxygen content. "The problem is that low oxygen also results in low strength," Bono says, explaining that oxygen in dilute amounts is an im- portant strengthening agent in titanium and the reason for the 0.17 percent oxgyen content of standard Grade 5 titanium. Carpenter's technical team modified the alloy's chemistry to create a powder that was still within Grade 5 strength specifi- cation, but better tailored to additive manufacturing. "We were able to give them very low oxygen by tightly controlling several other strengthening elements," Bono says. The resulting material more than met the strength require- ments of Grade 5 titanium. In fact, in testing CarTech Puris 5+ alloy consistently exceeded Grade 5 strength requirements by 20 percent. The virgin powder has an oxygen content of 0.13 percent, providing more space for recycling and reuse, while also reducing the burden of testing and the risk in the final part. Fur- thermore, the new composition enabled CalRam to meet both the strength and ductility requirements of the application. "Our ability to improve the alloy ultimately drove im- provements in their process," Murtagh says, referencing lower rejection rates and increased part strength achieved through CalRam's use of CarTech Puris 5+. "It has since become our most popular titanium alloy," Bono says. "We solved one customer's problem, but it's really indicative of a problem across the entire industry." Customized materials like this could be a major boon to manufacturers in the middle term. But in the long term, AM materials development will mean going back to the drawing board and creating new powders that are optimized for additive applications and systems from the beginning. "I think we're just scratching the surface in terms of new material development," Murtagh says. "The more we understand about the actual printing technologies and the design capabili- ties of additive, the more we can work on the front end to tailor materials for throughput, speed, repeatability and the properties you want in the final part." Carpenter's CarTech Puris 5+ is an example of a material that has been customized for AM. The titanium alloy features a lower oxygen content than standard Grade 5 Ti-6Al-4V, supporting more recycling and greater reliability in the powder-bed fusion process.

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