Researchers from RMIT University and the University of Sydney have developed a new class of strong, ductile, tunable, and sustainable titanium alloys. This research was conducted in collaboration with Hong Kong Polytechnic University and Swedish software developer Hexagon’s Manufacturing Intelligence division.
Titanium alloys are incredibly useful materials, and are prized for their strength, low weight, and resistance to corrosion and high temperatures. However, traditionally manufactured titanium alloys are expensive to produce.
This new research is said to offer potential for a new class of sustainable and cheap high-performance titanium alloys for use in aerospace, biomedical, chemical engineering, space, and energy applications. The team integrated alloy and 3D printing process design to develop their new titanium alloys, which are 3D printed from metal powders using Laser Directed Energy Deposition (L-DED).
According to lead researcher Professor Ma Qian from RMIT, the research team embedded circular economy into their design. These novel alloys can be produced from waste products and low-grade materials, without the need for expensive additives such as vanadium and aluminum. Instead, oxygen and iron, which are both cheap and abundant, are used.
“Reusing waste and low-quality materials has the potential to add economic value and reduce the high carbon footprint of the titanium industry,” commented Qian.
Lead author Dr Tingting Song from RMIT claimed that the team is “at the start of a major journey, from the proof of our new concepts here, towards industrial applications”.
“There are grounds to be excited – 3D printing offers a fundamentally different way of making novel alloys and has distinct advantages over traditional approaches. There’s a potential opportunity for industry to reuse waste sponge titanium-oxygen-iron alloy, ‘out-of-spec’ recycled high-oxygen titanium powders or titanium powders made from high-oxygen scrap titanium using our approach,” added Song.
The team’s research paper titled ‘Strong and ductile titanium-oxygen-iron alloys by additive manufacturing’, has been published in the journal Nature.
Developing new 3D printed titanium alloys
The team’s alloys consist of a mixture of two forms of titanium crystals, alpha-titanium phase and beta-titanium phase, called Ti-6Al-4V. Each form corresponds to a specific arrangement of atoms.
The most common titanium alloy, Ti-6Al-4V has been traditionally produced using 6% aluminum and 4% vanadium, and makes up over 50% of the entire titanium market. This new research replaces aluminum and titanium with oxygen and iron. In addition to being readily available and inexpensive, these elements are two of the most powerful stabilizers and strengtheners of alpha- and beta-titanium phases.
Traditionally, titanium alloys incorporating high levels of titanium and oxygen have faced challenges which have hindered their development and adoption.
“One challenge is that oxygen – described colloquially as ‘the kryptonite to titanium’ – can make titanium brittle, and the other is that adding iron could lead to serious defects in the form of large patches of beta-titanium,” said Qian.
L-DED 3D printing, a process generally used for manufacturing large and complex parts, allowed the researchers to overcome these challenges.
Using L-DED allowed the team to tune the mechanical properties of the alloys. The scientists produced nanoscale-sized titanium crystals within the alloy, carefully controlling the distribution of oxygen and iron atoms. This resulted in some specific parts of the alloy being strong, and others that are ductile, ensuring the material is not brittle under tension.
Using the DED module in Hexagon’s Simufact Welding program, the team 3D printed and tested a series of these configurations. After testing, the researchers found that their alloys could rival the ductility and strength of other commercial titanium alloys.
“The critical enabler is the unique distribution of oxygen and iron atoms within and between the alpha-titanium and beta-titanium phases,” explained Professor Simon Ringer, co-lead researcher from the University of Sydney.
“We’ve engineered a nanoscale gradient of oxygen in the alpha-titanium phase, featuring high-oxygen segments that are strong, and low-oxygen segments that are ductile allowing us to exert control over the local atomic bonding and so mitigate the potential for embrittlement.”
Developments in 3D printing alloys
This is not the first time 3D printing has been used in the development of metal alloys. Last year, researchers from RWTH Aachen University’s Chair for Digital Additive Production (DAP) used Extreme High-Speed Laser Material Deposition (EHLA) 3D printing to develop new alloys for laser powder bed fusion (PBF).
EHLA was originally developed in 2017 as Fraunhofer ILT’s take on high-volume directed energy deposition (DED). RWTH’s investigation compared both printing technologies’ process characteristics, yielding promising results with regards to the transferability of their material capabilities. From their findings, the DAP team deduced that it could qualify EHLA as a rapid alloy development platform for PBF 3D printing.
Elsewhere, NASA, the US National Aeronautics and Space Administration, have developed a novel metal 3D printing alloy for use in high-performance aerospace systems. Called GRX-810, this new material is an example of an oxide dispersion strengthened (ODS) alloy, a metal containing nanoscale oxide particles. This alloy is reportedly incredibly strong and durable, capable of withstanding temperatures of over 1090°C (2000°F).
“The nanoscale oxide particles convey the incredible performance benefits of this alloy,” commented Dale Hopkins, deputy project manager of NASA’s Transformational Tools and Technologies project.
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Featured image shows an Atomic-scale microstructure across an alpha-beta interphase interface from a new alloy 3D-printed by the team using laser directed energy deposition. Image via Ma Qian Simon Ringer and colleagues.
