Metal fatigue conquered


Rebecca Pool

Friday, March 10, 2017 - 13:15
Image: Beating fatigue in steel [MIT]
A team of researchers from the US, Japan and Germany have developed a novel steel that resists microcracks, that lead to fatigue failure.
By incorporating a laminated nanostructure to the steel the researchers induced a bone-like resilience that allows the steel to to deform without the propagation of microcracks.
"Fatigue failure creates enormous risks for all engineered structures, as well as for human lives," highlights Professor Cemal Cem Tasan from MIT. "Inspired by the excellent fracture toughness of bone, we decided to explore the fatigue resistance in metastability-assisted multiphase steels."
 A major factor in bone’s fracture resistance is its hierarchical and laminated structure, so the researchers set out to design a similar substructure to this, in steel.
The team focused on two key steels with an intrinsic hierarchical structure, comprising laminated martensite and metastable austenite phases, and made additional enhancements to the alloys to increase crack propagation resistance.
Cyclic mechanical loading indicated the steels had an exceptional fatigue limit and fatigue life relative to conventional steels used in automotive applications, with superior crack resistance.
Researchers developed a steel with three characteristics that help it resist microcracks that lead to fatigue failure: a layered nanostructure, a mixture of microstructural phases with different degrees of hardness, and a metastable composition. They compared samples of metal with just one or two of these key attributes (top left, top right, and bottom left) and with all three (bottom right). The metal alloy with all three attributes outperformed all the others in crack resistance. [MIT]
"Our results reveal that tuning the interface structure, distribution and phase stability to simultaneously activate the multiple micromechanisms that resist crack propagation is key to the leap in mechanical response," highlights Tasan.
According to Tasan, it remains to be seen what would be needed to scale up the material to the quantities required for commercial applications.
But as he adds: "This is an alloy that would be more expensive than a basic low-carbon steel but its property benefits have been shown to be quite exceptional, and it's with much lower amounts of alloying metals than other proposed materials."
Research is published in Science.
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