What do jet engines and spiderwebs have in common? They’re both made of remarkably strong yet lightweight materials. Spider silk is one of nature’s strongest and toughest fibres, woven from flexible, interconnected protein chains to create delicate threads stronger than steel.
In some ways, lamellar titanium aluminide (TiAl) is the aerospace sector’s spider silk: formed from alternating nanometre-thin layers of both metals, it’s a light and durable alloy with a high strength-to-weight ratio. Lamellar TiAl stays strong, even at extreme temperatures, making it a good choice for jet engine parts that heat up while operating, such as turbine blades.
However, at room temperatures, lamellar TiAl lacks ductility; compared to more common alloys like steel, it's brittle and prone to cracking, explained Balaji Selvarajou, a Scientist at A*STAR’s Institute of High Performance Computing (IHPC).
“The main hindrance to lamellar TiAl’s wider adoption is its low damage tolerance,” Selvarajou commented. “In steel, even if microscopic cracks form during fabrication or operation, it takes a considerable amount of force to propagate them. However, with lamellar TiAl, these cracks can grow with very little extra loading.”
This means making crack-free components from lamellar TiAl is difficult and expensive. Currently, the alloy is a viable material only for manufacturers who can absorb high costs, such as the aerospace and automotive industries, Selvarajou added.
Aiming to understand why lamellar TiAl tolerates damage poorly, Selvarajou and colleagues teamed up with the School of Materials Science and Engineering, Nanyang Technological University, Singapore, to design a study that investigated the different mechanisms involved when the alloy deforms. They developed a computational model that simulates how the alloy behaves under stress based on its microstructural features and external environment.
The computational model was powered by crystal plastic finite element modelling (CPFEM), which tracks microstructure formation under a range of loading forces and temperatures. To build the model, the researchers gathered published data on TiAl alloys fabricated under a wide range of experimental conditions.
“CPFEM allows us to incorporate both the effects of individual deformation mechanisms, and the interactions between them, on the alloy’s mechanical responses,” explained Selvarajou. “It captures all key aspects for deformation modelling including anisotropy, temperature and microstructure effects.”
Based on their simulation data, the researchers recommended adjustments that may improve lamellar TiAl’s hardiness, such as introducing trace elements or heat-treating the alloy before shaping. In addition, their work also overturned a common assumption in the field.
“It’s widely assumed that one way to increase TiAl ductility is to decrease the lamellar width,” said Selvarajou, referring to the distance between the alloy’s alternating layers. “However, we found that beyond a specific critical value, a thinner lamellar width doesn’t improve damage tolerance.”
The work creates the foundation for stronger future TiAl alloys that can be used in landbound industries such as nuclear power and chemical processing. “We would consider our work a success if it inspires other follow-up studies that help evolve lamellar TiAl into a widely used structural material,” said Selvarajou.
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing (IHPC).