Tailored hardening of ZrCuAl bulk metallic glass induced by 2D gradient rejuvenation

Autor: Wookha Ryu, Junji Saida, Rui Yamada
Rok vydání: 2020
Předmět:
Zdroj: NPG Asia Materials. 12
ISSN: 1884-4057
1884-4049
Popis: The work hardening behavior of bulk metallic glasses has not been previously ascribed to their intrinsic structure but rather to the introduction of other components that act as hardening elements. Here, we present clear evidence of a 2D gradient rejuvenation state that can induce tailored hardening of a monolithic bulk metallic glass. We show that the local free volume content related to the rejuvenation state controls the shear band angle and the maximum effective shear stress. Hence, shear band propagation is prohibited, and the formation of a complete shear plane transecting the whole specimen is blocked. The generation of plastic strain is accompanied by an increase in the critical shear stress, resulting in sustainable apparent hardening. In this way, we present a bulk metallic glass that has a tailored hardening mechanism and establish an experimental link between a gradient rejuvenation state and mechanical properties. A new apparatus for asymmetric heating of metallic glass can help these stronger-than-steel alloys avoid catastrophic failure. The random atomic structure of metallic glasses makes them tough and flexible, but also imparts uneven fatigue resistance that can cause cracks to form unexpectedly. Wookha Ryu and colleagues from Tohoku University in Sendai, Japan have now developed a technique to reinforce these alloys using controlled deformations to harden their structure. The team developed a device that contacts the top surface of a metallic glass for heating, or the bottom surface for rapid cooling. This approach introduces a gradient structure in which the gaps between atoms gradually widen. The increased free space changes the amount of atomic friction in the glass, enabling it to be hardened through deformation without creating stress points that initiate fractures. Tailored hardening behavior of monolithic bulk metallic glass (BMG) is demonstrated experimentally. A 2D gradient rejuvenation is introduced into ZrCuAl BMG by a novel heat treatment method. The gradual change of free volume realizes sustainable hardening until fracture. The local free volume related to the rejuvenation state controls the shear band angle and the maximum effective shear stress. Hence, shear band propagation is prohibited and the formation of a complete shear plane transecting the whole specimen is blocked. The current approach offers a new paradigm for utilizing hardening capability of BMG as practical engineering materials.
Databáze: OpenAIRE
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