Brittle-to-Ductile Transition in Metallic Glass Nanowires

Abstract

When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure.

Damage Accumulation in Silica Glass Nanofibers

“…Yet, recent experimental measurements revealed that nanoscale silica fibers become increasingly ductile as the size is decreased. [7][8][9][10][11][12] The origin of this puzzling sizeinduced brittle to ductile transition is still debated with possible explanations based on surface fluidization. 9,10 Indeed, experiments and simulations report evidence of a boundary layer where atoms are more mobile.…”

“…For example, silica glasses quenched under increasingly high pressures show enhanced ductility, 6 suggesting a role for increased defect concentration. Recent results are changing the conventional view of the brittle-to-ductile transition (BDT) suggesting that it is possible to induce ductility just by reducing the sample size towards the nanoscale, [7][8][9][10][11][12] as demonstrated for silica glass nanofibers under tensile load. 9,10 The physical origin of this sample-size induced BDT in silica glasses is currently debated.…”

“…than in metallic glass nanofibers11 where the crack is oriented at 45 • with respect to the loading direction, in SiO 2 glasses 9 the crack is oriented at 90 • . This is due to the fact that metallic glasses fail along the direction of maximum shear, while silica glasses fail along the direction of maximum tensile stress.…”

A dual fracture transition mechanism in nanotwinned Ni

“…Many researchers have observed brittle fracture and brittle-to-ductile transition (BDT) by experiments and simulations in materials, such as Silicon [1,2], Body Centred Cubic (BCC) [3][4][5] and glass [6], where the BDT was attributed to the ledge formation [1] and phase transformation [2,5]. Previous experiments showed that the bulk or coarsegrained Face Centred Cubic (FCC) materials tended to be a ductile fracture.…”

Rigidity-Controlled Crossover: From Spinodal to Critical Failure

“…In this Letter, we use an analytically tractable meanfield model to show that both spinodal and critical scaling behaviors can coexist near the threshold of the brittleto-ductile transition [25][26][27][28][29][30][31]. Ductile response is understood here in the sense of stable development of small avalanches representing micro-failure events [32,33].…”