By integrating alloying and 3D printing techniques, a team of researchers has created a new class of titanium alloys that are strong under stress and not brittle. The work, described as a breakthrough, promises a new class of more sustainable high-performance titanium alloys for applications in aerospace, biomedical, chemical engineering and energy. Leading the innovation were the Royal Melbourne Institute of Technology (RMIT) and the University of Sydney, in collaboration with Hong Kong Polytechnic University and Melbourne-based Hexagon Manufacturing Intelligence.
The team incorporated the idea of a circular economy into its design, creating promising opportunities for manufacturing the new titanium alloys from industrial waste and low-value materials, explained Ma Qian, RMIT professor and lead researcher. This offers added economic value and can reduce the high carbon footprint of the titanium industry, he said.
Alpha titanium phase and beta titanium phase
The team's titanium alloys consist of a mixture of two forms of titanium crystals, called alpha titanium phase and beta titanium phase, each corresponding to a specific arrangement of atoms. Since 1954, industrial titanium alloys have been produced primarily by adding aluminum and vanadium. The research team now investigated the use of oxygen and iron, two of the strongest stabilizers of the alpha and beta titanium phases.
"One challenge is that oxygen can embrittle titanium, and the other is that the addition of iron can lead to serious defects in the form of large areas of beta titanium," Qian explained.
The researchers combined their alloy concepts with the Laser Directed Energy Deposition (L-DED) 3D printing process. This allowed them to exert control over local atomic bonding and reduce the potential for embrittlement. In this way, they identified a series of strong, ductile and easy-to-print alloys that can compete with those of commercial alloys.
"We have developed a nanoscale oxygen gradient in the alpha titanium phase that has high oxygen content segments that are strong and low oxygen content segments that are ductile. This research provides a new titanium alloy system that offers a broad and tunable range of mechanical properties, high manufacturability, tremendous potential for emissions reduction, and insights for material design in related systems," said, University of Sydney Professor Simon Ringer, pro-vice-chancellor and co-principal investigator.
"Oxygen embrittlement is a major metallurgical challenge not only for titanium, but also for other important metals such as zirconium, niobium and molybdenum and their alloys. Our work could provide a template to reduce these oxygen embrittlement issues through 3D printing and microstructure design," added co-lead author Dr. Zibin Chen.
The team's research, "Strong and ductile titanium-oxygen-iron alloys by additive manufacturing," was published in the journal Nature.
