Wei Xiong in the Physical Metallurgy and Materials Design Laboratory. Photo: University of Pittsburgh.When creating an alloy out of multiple metals, defects and structural instability can sometimes occur in the material. Now, researchers at the University of Pittsburgh Swanson School of Engineering are harnessing those imperfections to make the material stronger while retaining its flexibility.
The researchers are designing metastable alloys that can overcome the well-known trade-off between strength and ductility, revealing a strategy for creating alloys suited to a broad range of applications. They report their work in a paper in Science Advances.
“Our work is showing how we can include intentional flaws in an alloy to make it stronger while retaining the ductility, or flexibility, of the material,” said Wei Xiong, assistant professor of mechanical engineering and materials science, whose Physical Metallurgy and Materials Design Laboratory led the study. “The techniques we are developing can be used to make materials fit for earthquake construction, naval ships, aerospace, nuclear energy, or even transportation for oil or hydrogen – all applications where a strong but flexible material is crucial.”
This study looks at two mechanisms for metastability engineering that can be used to create strong, ductile alloys: transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). TRIP and TWIP both utilize changes in the microstructure of an alloy that occur under pressure to form purposeful defects that can improve its strength.
“You can think of the strength and ductility of a material like plastic versus glass,” explained Xiong. “Plastic is much more ductile and flexible: it is not as strong, but you can bend it with your hands. Glass is stronger than plastic, but it’s also much less flexible and will break if you try to bend it. This is the trade-off that we are trying to overcome with alloys – something that has both strength and ductility.”
To conduct their study, Xiong worked with lead author Xin Wang, a graduate student in the Physical Metallurgy and Materials Design Laboratory, as well as researchers at the Illinois Institute of Technology and Northwestern University.
Using a modeling technique known as CALPHAD, supported by density functional theory calculations, the team was able to derive fundamental knowledge that they could then apply to developing metastable alloys with TRIP/TWIP for enhanced strength-ductility synergy. The same approach also can be applied to concentrated alloys like steel and nickel.
“We want to understand the unstable microstructure so we can predict the instability, and then we can use the defects to further increase strength and elongation,” said Wang. “The resulting material is then self-strengthening – deform it, and it actually gets stronger.”
This story is adapted from material from the University of Pittsburgh, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.