Thermomechanical Behavior of Molded Metallic Glass Nanowires

Abstract

Metallic glasses are disordered materials that offer the unique ability to perform thermoplastic forming operations at low thermal budget while preserving excellent mechanical properties such as high strength, large elastic strain limits, and wear resistance owing to the metallic nature of bonding and lack of internal defects. Interest in molding micro- and nanoscale metallic glass objects is driven by the promise of robust and high performance micro- and nanoelectromechanical systems and miniature energy conversion devices. Yet accurate and efficient processing of these materials hinges on a robust understanding of their thermomechanical behavior. Here, we combine large-scale thermoplastic tensile deformation of collections of Pt-based amorphous nanowires with quantitative thermomechanical studies of individual nanowires in creep-like conditions to demonstrate that superplastic-like flow persists to small length scales. Systematic studies as a function of temperature, strain-rate, and applied stress reveal the transition from Newtonian to non-Newtonian flow to be ubiquitous across the investigated length scales. However, we provide evidence that nanoscale specimens sustain greater free volume generation at elevated temperatures resulting in a flow transition at higher strain-rates than their bulk counterparts. Our results provide guidance for the design of thermoplastic processing methods and methods for verifying the flow response at the nanoscale.

The Mechanical Properties of Nanowires

“…The AFM‐based three‐point bending test has been used for characterizing the elastic modulus of various NWs, including Si, Ge, BN,LaB 6 , TiSi 2 , NiC, SiC, Na 4 Mn 9 O 18 , SiO 2 , SrB 2 O 4 , Co 3 O 4 /CoO, ZnO, and metallic glasses . A sharp AFM tip may cause damage to the NW being tested, as shown in Figure b.…”

Synthesis and characterization of ultralong SiC nanowires with unique optical properties, excellent thermal stability and flexible nanomechanical properties

“…To date, various techniques for measuring the mechanical behaviors and properties of individual NWs have been developed, such as in situ bending tests 11 , tensile tests 12 – 15 , resonant frequency tests 16 and nanoindentation 17 , and investigations on the mechanical properties of the NWs have been reported in the literature. Lieber et al .…”

Fabrication and Properties of Micro‐ and Nanoscale Metallic Glassy Wires: A Review

“…[68] In addition, the prediction shown in Figure 11 that the critical length scale varied with strain rate is consistent with experiments in a literature. [75,76] [72] The critical length scale of the transition decreases with increasing temperature at intermediate temperatures (300-400 K).…”

“…If the diameters of MG wires are smaller than the sizes of STZs, no physical model could tell how the deformation of the wires would be mediated, and no experiment has been done to shown that because MG samples with thickness comparable to STZ size have not been fabricated. [57] In addition, surface induced strong free volume gradient [75] or stress gradient [82] may exist at this small length scale and increase strength. However, many research works suggested that surface diffusion effect would dominate the deformation of MG at the length scale of STZ (i.e., %1 nm) [41,59,80,81] and decrease the strength.…”

“…Cohen and Turnbull [1] had predicted that metallic liquid would had gone through glass transition, if it had been sufficiently undercooled and crystallization had been bypassed, when Duwez reported the first rapid quenched MG of Au 75 Si 25 in 1960. [2] The stage for the explosive growth of work on MGs had been set by Pond and Maddin [3] who invented a melt-spun technique for preparing MG ribbons, because it opened the possibility of large scale production.…”