Carbon molds for use in the fabrication of bulk metallic glass parts and molds

Abstract

Novel molds and methods for Bulk Metallic Glass (BMG) molding using carbon templates obtained from pyrolyzed materials are provided. The method employs the Carbon MEMS (C-MEMS) technique to derive molds of different geometries and dimensions. The resultant carbon structures are stable at very high temperatures and have sufficient mechanical strength to be used as master molds for the thermoplastic forming of BMGs.

1 . A method for shaping a bulk-metallic glass material using thermoplastic forming comprising:
 patterning a master shape into a material, said material having the ability to substantially maintain its shape during pyrolysis;   pyrolyzing said master shape into a carbon mold, said carbon mold being capable of withstanding the temperatures and pressures necessary to shape the bulk-metallic glass under thermoplastic forming conditions; and   thermoplastically forming the bulk-metallic glass material on the carbon mold to form a shaped bulk-metallic glass article.   
     
     
         2 . The method of  claim 1 , wherein the material is a polymeric material selected from the group consisting of photoresists and organic polymers. 
     
     
         3 . The method of  claim 2 , wherein the polymeric material is selected from the group consisting of SU-8, poly(methyl methacrylate) (PMMA), phenolic resins, polyfurfuryl alcohols, cellulose, polyvinyl chloride and polyimides. 
     
     
         4 . The method of  claim 1 , wherein the step of patterning includes a process selected from the group consisting of stamping, casting, machining, CNC machining, electrical discharge machining (EDM), electrochemical machining (ECM), wet bulk machining, milling, ion beam milling), lithography, photolithography, X-ray lithography, gray-scale lithography, electron beam lithography (EBL), nanoimprint lithography (NIL) and focused-ion beam (FIB). 
     
     
         5 . The method of  claim 1 , wherein the step of patterning is carried out by photolithography, and further comprising inserting a filler between the photolithographic light source and the material to prevent T-topping in the master shape. 
     
     
         6 . The method of  claim 4 , wherein the step of patterning is carried out by photolithography, and wherein the photolithographic pattern is formed by a high-resolution chromium-on-quartz photomask patterned with an e-beam tool. 
     
     
         7 . The method of  claim 1 , wherein the master shape is formed of a pre-patterned biomaterial. 
     
     
         8 . The method of  claim 1 , wherein the master shape comprises a free-standing structure. 
     
     
         9 . The method of  claim 8 , wherein the master shape is formed on a substrate, and wherein the substrate layer in contact with the master shape and the material of the master shape have good coefficient of thermal expansion matching. 
     
     
         10 . The method of  claim 9 , wherein the substrate layer in contact with the master shape and the master shape are formed of the same material. 
     
     
         11 . The method of  claim 10 , wherein the material is SU-8. 
     
     
         12 . The method of  claim 9 , wherein the substrate layer in contact with the master shape comprises a transparent polymeric film. 
     
     
         13 . The method of  claim 12 , wherein the transparent polymeric film is selected from the group consisting of polyimide or polyester. 
     
     
         14 . The method of  claim 1 , wherein the master shape comprises undercuts and overlays. 
     
     
         15 . The method of  claim 14 , wherein the polymeric master shape is patterned using a process selected from the group consisting of multi-layer photolithography and grayscale lithography. 
     
     
         16 . The method of  claim 1 , wherein the material is disposed on a substrate during patterning, and wherein the substrate is made from a material selected from the group consisting of silicon, silicon oxide, silicon nitride, glass, quartz, polyethylene terephthalate, polyimide and the polymeric material. 
     
     
         17 . The method of  claim 1 , wherein the material is patterned such that the walls of said master shape have a positive slope. 
     
     
         18 . The method of  claim 1 , further comprising separating the bulk-metallic glass article from said carbon mold. 
     
     
         19 . The method of  claim 18 , wherein the step of separating uses a process selected from the group consisting of wet immersion, plasma ion etching, reactive ion etching, isotropic etching, mechanical scraping, thermal heating, sonication, and a combination thereof. 
     
     
         20 . The method of  claim 1 , wherein the bulk-metallic glass is selected from the group consisting of Zr-based, Ti-based, Fe-base, Ni-based, Mg-based, Cu-based and Co-based alloys. 
     
     
         21 . The method of  claim 1 , wherein the bulk-metallic glass has a supercooled liquid region (ΔTsc) of at least 30° C. 
     
     
         22 . The method of  claim 1 , wherein the step of thermoplastically forming comprises a technique selected from the group consisting of net-shape processing, micro-replication, nano-replication, extrusion, and superplastic forming. 
     
     
         23 . The method of  claim 1 , further comprising shaping a further material on said bulk-metallic glass article. 
     
     
         24 . The method of  claim 23 , wherein the step of shaping includes using the bulk-metallic glass article as a mold. 
     
     
         25 . The method of  claim 23 , wherein the further material is a polymer, metal or bulk-metallic glass having a molding temperature lower than that of the underlying bulk-metallic glass article. 
     
     
         26 . The method of  claim 24 , wherein the bulk-metallic glass mold is crystallized and the further material is the same bulk-metallic glass material used to make the mold. 
     
     
         27 . The method of  claim 1 , wherein the material is partially carbonized. 
     
     
         28 . The method of  claim 27 , wherein the step of thermoplastic forming further includes infiltrating the bulk-metallic glass material into the partially carbonized mold. 
     
     
         29 . The method of  claim 28 , wherein the bulk-metallic glass article formed is one of either a bulk-metallic glass foam or a carbon/bulk-metallic glass composite. 
     
     
         30 . The method of  claim 1 , further comprising using the carbon mold to form a new master shape and pyrolyzing this new polymeric master shape such that the features of the master shape undergo isometric reduction in size prior to thermoplastically forming the bulk-metallic glass. 
     
     
         31 . The method of  claim 30 , further comprising repeating the step of forming a new master shape until feature sizes of desired dimension are obtained. 
     
     
         32 . The method of  claim 1 , wherein the critical dimensions of the features of the master shape are less than 100 nm. 
     
     
         33 . A mold for thermoplastically forming a bulk-metallic glass comprising a carbonized master shape, wherein said carbonized master shape is formed of a material capable of withstanding the temperatures and pressures necessary to shape the bulk-metallic glass under thermoplastic forming conditions. 
     
     
         34 . The mold of  claim 33 , wherein the carbonized master shape is formed from a glass-like-carbon, and wherein the glass-like-carbon is formed by carbonizing a material selected from the group consisting of photoresists and organic polymers. 
     
     
         35 . The mold of  claim 33 , wherein the master shape comprises undercuts and overlays. 
     
     
         36 . The mold of  claim 33 , wherein the walls of the master shape have a positive slope. 
     
     
         37 . The mold of  claim 33 , wherein the critical dimensions of the features of the carbonized polymeric master shape are less than 100 nm.