Sub-Micron Feature Patterning of Thermoplastics using Multi-Scale BMG Tooling

Abstract

One potential application for Bulk Metallic Glasses (BMGs) is in dies with micro- and nano-sized features. Three basic characteristic sets inherent to BMGs make them ideal materials for micro/nano-tooling applications: (1) excellent compressive strength, wear and corrosion resistance; (2) amorphous structure which presents no microstructural length scale limitation to cutting and forming operations; (3) the presence of a glass transition temperature above which they can be easily formed. There are many potential applications for multi-scale BMG tooling, including in production of microfluidic and other precision biomedical devices. In the current work, discs were cut from 5 mm diameter cylindrical specimens of Zr44Cu40Al8Ag8 BMG produced via arc melting and casting into water-cooled copper molds. The cylindrical specimens were then thermoplastically formed into thin coin-like disc samples. The thin disc-shaped plates were then ground and polished to create a smooth flat surface. Sub-micron-sized features were patterned into the plates via a focused ion beam. We demonstrated that such feature sizes are not achievable in conventional crystalline metallic tool materials. The patterned BMG tools were then set in a compression press where the platen temperature was precisely controlled and a series of load-controlled embossing trials were carried out in which the features of the BMG tooling were replicated in poly(methyl methacrylate) (PMMA) sheet. An exercise in mapping out the size limitation of such a multi-scale embossing operation is reported.