A piece of alloy stress tested in Levente Vitos' lab at KTH. (Photo courtesy Levente Vitos.)
A piece of alloy stress tested in Levente Vitos' lab at KTH. (Photo courtesy Levente Vitos.)

Scientists at the KTH Royal Institute of Technology in Stockholm, Sweden, have developed a new way to improve the mechanical strength of superalloys that withstand extremely high temperatures.

Levente Vitos, professor at the institute, found that a phenomenon related to the invariant (invar) effect, which enables magnetic materials such as nickel-iron (Ni-Fe) alloys to keep from expanding with increasing temperature, was present in paramagnetic, or weakly magnetized, high-temperature alloys.

Invar has two known effects: thermal expansion and elasticity (the ability to spring back after bending). Because both of these effects are linked with the interplay between temperature and magnetic order, they are considered to be specific to magnetically-ordered alloys. Using first-principles quantum mechanical modeling, the researchers identified how invariant plasticity also occurs in non-magnetic alloys, when a structural balance exists at the atomic level between cubic and hexagonal close-packed structures.  

Invar plasticity enables magnetically-disordered Ni-Fe alloys to show practically invariant deformation behavior over a wide temperature range – making them suitable for turbines and other mechanical uses in extremely high temperatures. While the invar effect has never been fully understood, the new findings could help explain the high-temperature properties of special alloys used in jet engines, such as nickel-based superalloys, Vitos said.

‘Our findings create a new platform for tailoring high-temperature properties of technologically relevant materials towards plastic stability at elevated temperatures,’ said Vitos.

The research was supported by the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Swedish Foundation for International Cooperation in Research and Higher Education (STINT).

This story uses material from KTH, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.