Metallic glasses: viable tool materials for the production of surface microstructures in amorphous polymers by micro-hot-embossing

Abstract

Metallic glasses possess unique mechanical properties which make them attractive materials for fabricating components for a variety of applications. For example, the commercial Zr-based metallic glasses possess high tensile strengths (≈2.0 GPa), good fracture toughnesses (≈10-50 MPa √ m) and good wear and corrosion resistances. A particularly important characteristic of metallic glasses is their intrinsic homogeneity to the nanoscale because of the absence of grain boundaries. This characteristic, coupled with their unique mechanical properties, makes them ideal materials for fabricating micron-scale components, or high-aspect-ratio micro-patterned surfaces, which may in turn be used as dies for the hot-embossing of polymeric microfluidic devices. In this paper we consider a commercially available Zr-based metallic glass which has a glass transition temperature of T g ≈ 350 • C and describe the thermoplastic forming of a tool made from this material, which has the (negative) microchannel pattern for a simple microfluidic device. This tool was successfully used to produce the microchannel pattern by micro-hot-embossing of the amorphous polymers poly(methyl methacrylate) (T g ≈ 115 • C) and Zeonex-690R (T g ≈ 136 • C) above their glass transition temperatures. The metallic glass tool was found to be very robust, and it was used to produce hundreds of high-fidelity micron-scale embossed patterns without degradation or failure.

A thermoplastic forming map of a Zr-based bulk metallic glass

“…Since the channels are long enough compared to their width, and there are a large number of them aligned in parallel, we employed a plane strain idealization in our simulations and consider only continuous bends with suitable boundary conditions [26,36]. A friction coefficient of 0.25 between the silicon and the metallic glass was selected.…”

“…Taking advantage of BMGs' superplastic flow in the supercooled liquid region (SCLR), thermoplastic forming (TPF) has been widely employed to fabricate precise and versatile geometries on length scales ranging from 10 nm to several centimeters [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The formability has been proposed to be the key property that determines the suitability of BMGs for TPF [37][38][39][40][41][42].…”

Criticality in Bulk Metallic Glass Constituent Elements

“…14 These properties have triggered wide commercial exploration of BMGs. [15][16][17] One of the most unusual and useful attributes of BMGs are that they escape the typical materials trade-off of processibility versus properties. 18 The high stability against crystallization results in a supercooled liquid region that enables thermoplastic forming (TPF) similar to the processing of thermoplastics.…”

“…18 Thus, BMGs can be considered high-strength metals that can be processed like plastics. 18,19 TPF-based processes for BMGs like blow-molding, 18 extrusion, 20,21 compression molding, 22,23 micro-and nano-molding, 17,24 and hot-rolling 25 permit BMGs to be formed into many complex shapes on various length scales.…”

Manufacturing microstructured tool inserts for the production of polymeric microfluidic devices

“…Further, the micro-machining process usually leaves machining marks and burrs, which can result in a poor surface finish [12].…”