Controllable nanoimprinting of metallic glasses: effect of pressure and interfacial properties

Kumar, Golden; Bławzdziewicz, Jerzy; Schroers, Jan

doi:10.1088/0957-4484/24/10/105301

Cited by 49 publications

(20 citation statements)

References 27 publications

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“…Further increase in strain rate results in solid-like yielding and inhomogeneous (shear-localized) deformation in MG supercooled liquids [40,41]. Low strain rates are used for thermoplastic molding because the Newtonian behavior of MG supercooled liquids can be precisely described using constitutive equations to model the shaping process [44,45]. In addition, low strain rate loading minimizes the risk of premature template failure.…”

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confidence: 99%

High strain rate thermoplastic demolding of metallic glasses

Hasan

Kumar

2016

Scripta Materialia

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Silicon templates are ideal for thermoplastic patterning of metallic glasses but their thermal expansion mismatch prevents demolding without chemical etching. Besides limiting the template life, chemical exposure alters the surface chemistry and properties of metallic glasses. To overcome these issues, we develop thermoplastic demolding which enables template reusability and fabrication of pristine metallic glass structures. Chemicalfree demolding allows decoupling of topographic and compositional effects on properties of metallic glasses. We show that mechanically and chemically demolded samples exhibit distinct wetting behavior despite similar topography. The versatility of demolding technique is demonstrated for structures of different shapes and metallic glass formers.Patterning is an effective route to change the surface properties such as adhesion [1][2][3][4], cell-response [5,6], friction [7,8], reflectance [9,10], and wetting [3,11,12]. Numerous techniques such as lithography [13][14][15], embossing [16][17][18], self-assembly [19,20], electrochemical etching [21], and laser processing [22] have been developed for patterning of semiconductors and polymers. These methods are either not readily applicable to metals or require complex hardware. Metallic glasses (MGs) are unique alloys of metals which can be patterned by simple thermoplastic methods due to the existence of their supercooled liquid state [23][24][25][26][27]. This is achieved by molding of MGs against templates heated above the glass transition temperature (T g ) followed by cooling below T g and demolding [27]. MG surfaces textured with micro [28-30], nano [31][32][33], and hierarchical [34] structures have been synthesized by using suitable templates. Structures harvested from the patterned surfaces have also been used for characterization of size-effects in MGs [35]. However, in all these cases the templates are chemically etched away to release the MGs. Use of chemicals not only limits the template reusability but can also affect the properties of molded MGs. It has been reported that KOH typically used for wet etching of silicon and alumina templates can de-alloy some Zr-based MGs [36]. KOH is known to decrease the hydrophobicity of materials by altering the surface chemistry and topography [37]. Size-effects are also very sensitive to the processing conditions in MGs due to their metastable structure [38]. Therefore, chemical-free demolding of templates is essential to use thermoplastic fabrication for surface engineering and characterization of small structures in MGs.Mechanical separation of templates and MGs after thermoplastic molding is prevented by their thermal expansion mismatch (Fig. 1). The coefficient of thermal expansion (α) for MG formers is often higher than templates (Table 1). But any combination of mismatch in α (α MG N α template or α MG b α template ) results in thermal stress build up on the multiple MG-template interfaces during cooling below T g (Fig. 1a). To estimate the extent of residual thermal stress, a 2D th...

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Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

High strain rate thermoplastic demolding of metallic glasses

Hasan

Kumar

2016

Scripta Materialia

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“…Compared to conventional polycrystalline alloys, BMGs exhibit high strength, hardness, wear resistance, and elastic strain limit [4,5]. When heated into the supercooled liquid state near the glass-transition temperature T g , they show good plastic formability (fluidity) [6] which can exploited both for such macroscopic processes as blow-molding [7] as well as precision forming on micrometer and even nanometer scales [8]. The combination of high strength and high formability is considered particularly attractive.…”

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confidence: 99%

Influence of cyclic loading on the onset of failure in a Zr-based bulk metallic glass

et al. 2014

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Samples of Zr 62.5 Cu 22.5 Fe 5 Al 10 bulk metallic glass are subjected to uniaxial compression. Comparison of tests in monotonic loading and cyclic loading (repeated loading to the onset of plasticity, then unloading) shows that the compressive plasticity of the glass is drastically reduced under cyclic loading. It is argued that this effect arises from stress reversal accelerating the concentration of shear on a dominant shear band. The link with compression-compression fatigue results, and the consequences for low-cycle fatigue of metallic glasses are considered.

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“…Prior work on nanoscale forming of BMGs has implicitly assumed no size-dependence in process-relevant thermophysical properties. [2][3][4][5][6][7] However, deviations from bulk behavior have been reported for performance-related properties including strength, 8 plasticity, 9,10 and elasticity, 11 even though their origin is still debated. 12 From this perspective, the question of sizedependence of thermophysical properties of BMGs is a fundamentally compelling one which also has important implications for engineering nanofabrication processes using BMGs.…”

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Finite size effects in the crystallization of a bulk metallic glass

Gopinadhan

Shao

Liu

et al. 2013

Applied Physics Letters

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Articles you may be interested inTemperature dependence of the thermoplastic formability in bulk metallic glasses Wetting of bulk metallic glass forming liquids on metals and ceramicsWe explore finite size effects in the crystallization of a bulk metallic glass with nm-scale dimensions. Nanorods of Pt 57.5 Cu 14.7 Ni 5.3 P 22.5 are produced by thermoplastic extrusion of supercooled liquid through a nanoporous template. The nanorods exhibit remarkable differences in their crystallization behavior above the glass transition. Crystallization for 100 and 200 nm diameter nanorods occurred at 6 and 24 C lower, respectively, than the nominal crystallization temperature for bulk material while the glass transition temperatures were unchanged from the bulk value. Size dependent crystallization kinetics is discussed within a framework of classical nucleation theory, as well as possible shear and surface-induced effects. V C 2013 AIP Publishing LLC. [http://dx.

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Controllable nanoimprinting of metallic glasses: effect of pressure and interfacial properties

Cited by 49 publications

References 27 publications

High strain rate thermoplastic demolding of metallic glasses

High strain rate thermoplastic demolding of metallic glasses

Influence of cyclic loading on the onset of failure in a Zr-based bulk metallic glass

Finite size effects in the crystallization of a bulk metallic glass

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