Super-strong, highly ductile and ultra-light alloys are now possible thanks to the innovative use of additive manufacturing (AM), or 3D printing, according to a materials research team at City University of Hong Kong (CityU).

The CityU-led project opens a new area in AM for the design of unprecedented titanium (Ti) alloys that are unachievable by conventional manufacturing methods and that hold great promise for a rich variety of structural applications.

“Our alloy development team unveils the promising possibility of utilising AM to design unique heterogeneous alloys with novel microstructure and supreme properties,” explained Professor Liu Chain-tsuan, University Distinguished Professor in the College of Engineering at CityU.

Professor Liu is the main supervisor behind this project while Dr Zhang Tianlong, a postdoc in the Department of Materials Science and Engineering, conducted the experiments and alloy design. Their paper has been published in top academic journal Science as “In situ design of advanced titanium alloy with concentration modulations by additive manufacturing”.

The new Ti-alloys are significant for several reasons, one being their weight. Whereas steel is generally 7.9 grammes per cubic centimetre, the new alloys are only 4.5 grammes per cubic centimetre, making them more than 40% lighter. 

“Light materials are hugely beneficial to, for instance, the design of airplanes,” Professor Liu explained.

The method for constructing the new alloys is notable, too, according to Dr Zhang, who completed his PhD earlier this year at CityU under Professor Liu’s supervision. 

“AM is a totally different process from conventional methods for material manufactures, and its unique features provide us with a greater freedom in designing alloy microstructures and properties,” said Dr Zhang. 

“Our innovative pathway can design materials by using a technique called laser-powder bed fusions to modulate the concentration of metals,” he added. Laser-powder bed fusions uses a tiny laser or electron beam to meld together the material powders. Adding microscopic materials such as iron into the mix during the AM process using this technique can make the overall alloy much, much stronger. 

This procedure is important because metallurgists tend to think that a lack of uniformity in alloy composition is undesirable because it leads to bad material properties. However, the team found that they can actively control the uniformity of the new alloys for advanced microstructures and properties. 

“What we have unveiled in our Science paper is the potential of AM in designing materials rather than simply designing geometries. Specifically, we have proposed a partial homogenisation method to produce Ti-alloys with micrometre scale concentration gradients with the aid of AM, which is not achievable by any conventional methods,” Dr Zhang added.

The next stage of the project is to conduct further tests on the strength, ductility, etc. of the new Ti-alloys with the aim to transfer the research results to industries related to materials science and engineering at a future date, said Professor Liu. 

“Our unprecedented research has excellent prospects for developing excellent new materials for industry,” he said.

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