Strain-hardening in metallic glasses

March, 2020

Strain(work)-hardening is the main reason that alloys are significant structural materials. It ensures that flow is delocalized, imparts ductility and inhibits catastrophic mechanical failure. Metallic glasses (MGs) have desirably high yield stress and elastic strain limit, but they show strain-softening, leading to severe flow localization in shear bands and thereby to failure in tension without significant ductility. A collaboration between the IMR (Shenyang, China) and DMSM has now overturned the paradigm that MGs must strain-soften.

The generally accepted explanation of strain-hardening was given by G.I. Taylor in 1934: plastic flow involves the motion and proliferation of dislocations, and the hardening reflects increasing inhibition of their motion. In 1956, P.B. Hirsch’s group observed motion of dislocations. These firsts at Cambridge are now followed by work, which (after 85 years) reveals an entirely new type of strain-hardening in alloys ‒ accompanied by a fall in the energy of the sample, rather than a rise as in Taylor’s case.