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The team, from City University of Hong Kong (CityU), said the research could lead to more alloys with ‘unprecedented’ structures and properties suitable for structural applications.
Most people consider 3D printing as a technology that can produce machine parts with complex shapes in just one step, said first author Dr Zhang Tianlong. “However, we unveiled that it has important potential in designing materials, rather than simply designing geometries.”
Metallurgists tend to think that a lack of uniformity in alloy components is undesirable because it leads to bad properties, such as brittleness. One of the key issues in additive manufacturing is how to eliminate this inhomogeneity during fast cooling. Dr Tianlong’s previous modelling and simulation found that a certain degree of heterogeneity in components can produce unique and heterogeneous microstructures that enhance alloy properties, however, so he tried to put those findings into reality.
"The unique features of additive manufacturing provide us with a greater freedom in designing microstructures," Dr Tianlong said.
"Specifically, we have developed a partial homogenisation method to produce alloys with micrometre-scale concentration gradients with the aid of 3D printing, which is unachievable by any conventional methods of material manufacturing.”
The method involves melting and mixing two different alloy powders and stainless steel powders using a focused laser beam. By controlling parameters like laser power and scanning speed during the 3D printing process, the team successfully created non-uniform composition in a controllable way.
"In addition to the use of additive manufacturing, the composition of the two-powder mixture is another key to creating the unprecedented lava-like microstructures with a high metastability in the new alloy,” said research leader Professor Liu Chain-Tsuan. "These unique microstructures give rise to the supreme mechanical properties, allowing the alloy to be very strong but ductile, and lightweight.”
While stainless steel is generally 7.9g/cm3, the new alloy is only 4.5g/cm3, making it roughly 40% lighter. In the team’s experiments, the titanium alloy with lava-like microstructures exhibited a high tensile strength of about 1.3 gigapascals, with a uniform elongation of about 9%. It also had an excellent work-hardening capacity of over 300 megapascals, which provides a large safety margin prior to fracture.
"These excellent properties are promising for structural applications in various scenarios, such as the aerospace, automotive, chemical, and medical industries," said Professor Chain-Tsuan.
"As the first team to use 3D printing to develop new alloys with unique microstructures and properties, we will further apply this design idea to different alloy systems, to further explore other properties of the new alloys."
The research was published in Science.
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