8 A new generation of superalloys is opening up new opportunities for UAV and space system design with additive manufacturing, writes Nick Flaherty. US space agency NASA is licensing a 3D-printable superalloy that can handle extreme temperatures to four US companies. At the same time, researchers at Purdue University have developed a superalloy of aluminium. The GRX-810 alloy developed by NASA has been used for liquid rocket engine injectors, combustors, turbines and hotsection components capable of enduring temperatures in excess of 1100 C. The laser 3D-printing process fuses metals together, layer by layer. Nanoparticles containing oxygen atoms spread throughout the alloy enhance its strength. Compared to other nickel-base alloys, GRX-810 can endure higher temperatures and stress, and it can last up to 2,500 times longer. It is also nearly four times better at flexing before breaking and twice as resistant to oxidation damage. “GRX-810 represents a new alloy design space and manufacturing technique that was impossible a few years ago,” said Dr. Tim Smith, materials researcher at NASA’s Glenn Research Centre, which developed the superalloy. In the USA, this has been licensed to Carpenter Technology of Reading in Pennsylvania, Elementum 3D of Erie in Colorado, Linde Advanced Material Technologies of Indianapolis and Powder Alloy of Loveland in Ohio. The engineers at Purdue University created a patent-pending process to develop ultra-high-strength aluminium alloys combining cobalt, iron, nickel and titanium using nanoscale, laminated, deformable intermetallics. These transition metals have traditionally been avoided in the manufacture of aluminium alloys. Intermetallics have crystal structures with low symmetry and are known to be brittle at room temperature, but this method forms the transitional metal elements into colonies of nanoscale, intermetallic lamellae that aggregate into fine rosettes. These nanolaminated rosettes can largely suppress the brittle nature of the intermetallics. “Our work shows that the proper introduction of heterogenous microstructures and nanoscale medium-entropy intermetallics offers an alternative solution to designing ultra-strong, deformable aluminium alloys via additive manufacturing,” said Prof Xinghang Zhang at Purdue. “These alloys improve upon traditional ones that are either ultrastrong or highly deformable, but not both.” Researcher Anyu Shang said: “Most commercially available, high-strength aluminium alloys cannot be used in additive manufacturing. They are highly susceptible to hot cracking, which creates defects that could lead to the deterioration of a metal alloy.” “The highest strength that these alloys achieve is in the range of 300500 megapascals, which is much lower than what steels can achieve, typically 600-1,000 megapascals,” said Prof Haiyan Wang. “There has been limited success in producing high-strength aluminium alloys that also display beneficial, large, plastic deformability.” “The heterogeneous microstructures contain hard, nanoscale intermetallics and a coarse-grain aluminium matrix, which induces significant back stress that can improve the work hardening ability of metallic materials. “Additive manufacturing using a laser can enable rapid melting and quenching, and thus introduce nanoscale intermetallics and their nanolaminates,” she added. During tests, the alloys showed a combination of prominent plastic deformability and high strength over 900 megapascals. The micropillar tests displayed significant back stress in all regions, and certain regions had flow stresses exceeding a gigapascal. Materials 3D-printable superalloy survives extreme temperatures Platform one August/September 2024 | Uncrewed Systems Technology A superalloy for space applications (Image courtesy of NASA)
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