Fine-tuning alloys for high temps

Superalloys that withstand extremely high temperatures soon could be tuned even more finely for specific properties, such as mechanical strength, as a result of new findings.

A phenomenon related to the invar effect — which enables magnetic materials like nickel-iron alloys to keep from expanding with increasing temperature — was reported to have been discovered in paramagnetic, or weakly magnetized, high-temperature alloys.

Levente Vitos, professor at KTH Royal Institute of Technology in Stockholm, said the breakthrough research, which includes a general theory explaining the new invar effect, promises to advance the design of high-temperature alloys with exceptional mechanical stability. The research team was led by him and composed of KTH Royal Institute of Technology researchers Zhihua Dong, Wei Li and Stephan Schönecker.

A piece of alloy is stress-tested at a lab at KTH Royal Institute of Technology. Image courtesy of L. Vitos

Short for “invariant,” invar plasticity allows magnetically disordered nickel-iron alloys to show practically invariant deformation behavior over a wide temperature range, making them ideal for turbines and other mechanical uses in extremely high temperatures.

The invar effect, however, never has been fully understood, and Vitos said these new findings help explain the peculiar high-temperature properties of special alloys used in jet engines, such as nickel-base superalloys.