Forest Products Laboratory

Title: Shear transformation zone activation during deformation in bulk metallic glasses characterized using a new indentation creep technique

Author: Puthoff, J.B.; Cao, H.B.; Jakes, Joseph E.; Voyles, P.M.; Stone, D.S.

Date: 2009

Source: Local structure and dynamics in amorphous systems [electronic resource]. Materials Research Society symposium proceedings ; v. 1152. Warrendale, Pa. : Materials Research Society, [2009] : [6] pages. ISBN: 9781605111247: 1605111244.

Description: We have developed a novel type of nanoindentation creep experiment, called broadband nanoindentation creep (BNC), and used it to characterize the thermal activation of shear transformation zones (STZs) in three BMGs in the Zr-Cu-Al system. Using BNC, material hardness can be determined across a wide range of strain rates (10^–4 to 10 s^–1) in a single experiment at room temperature. This data can be used to characterize the kinetics of deformation, including the free energy function (ΔG) for thermally-activated deformation. We have found that the activation energy agrees with the theory of Johnson and Samwer, in which ΔG ∝ [(τ_c – τ)/τ_c]^3/2, where τ is the flow stress and τ_c is the flow stress at 0K. In the context of their model, we estimate that the volume of an STZ is ~ 100-300 atomic volumes and the activation energies for low-stress deformation are 5-10 eV. From these measurements, it is possible to reproduce the temperature dependence of the flow stress.

Keywords: Metallic glasses, materials, creep, testing, strains, stresses, deformations, nanotechnology, nanostructured materials, measurement, zirconium, copper, aluminum, hardness, shear, temperature, elasticity, broadband nanoindentation creep, BNC, creep, kinetics, nanoindentation

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Citation

Puthoff, J.B.; Cao, H.B.; Jakes, Joseph E.; Voyles, P.M.; Stone, D.S.  2009.  Shear transformation zone activation during deformation in bulk metallic glasses characterized using a new indentation creep technique.   Local structure and dynamics in amorphous systems [electronic resource]. Materials Research Society symposium proceedings ; v. 1152. Warrendale, Pa. : Materials Research Society, [2009] : [6] pages. ISBN: 9781605111247: 1605111244..