Method and System for Fabricating Bulk Metallic Glass Sheets

Abstract

This invention describes a method and hardware of how to deform metallic glasses under low force and stabilized conditions to fabricate thin and large area metallic glass sheets. It is based on a combination of thermoplastic rolling and stretching and typically combined with a pre-heating method. The predominant mode of deformation is dependent on the BMG conditions such as thickness, viscosity, and crystallization time.

1 . A method of fabricating a bulk metallic glass sheet, the method comprising the steps of:
 a) preheating a bulk metallic glass feedstock to a temperature sufficient to soften the bulk metallic glass feedstock but that does not significantly contribute to a consumed crystallization time of the bulk metallic glass; and   b) thermoplastically rolling the pre-heated bulk metallic glass feedstock between a set of heated rollers maintained at a processing temperature of the bulk metallic glass; and   c) stretching the bulk metallic glass sheet after the bulk metallic glass sheet exits the set of heated rollers;   wherein the bulk metallic glass feedstock is reduced in thickness to produce a bulk metallic glass sheet; and   wherein processing conditions during steps a) to c) are such that a Reynolds number Re<10 −3  of the bulk metallic glass is maintained.   
     
     
         2 . (canceled) 
     
     
         3 . The method according to  claim 1 , wherein the pre-heating temperature is between about 0.8 times the glass transition temperature, T g , and 1.4 times the glass transition temperature, as measured in degrees Celsius, of the bulk metallic glass feedstock. 
     
     
         4 . (canceled) 
     
     
         5 . The method according to  claim 1 , wherein stretching occurs in a negative temperature gradient. 
     
     
         6 . The method according to  claim 1 , wherein stretching occurs by a controlled velocity. 
     
     
         7 . The method according to  claim 1 , wherein steps a) to c) are repeated to obtain a desired thickness of the bulk metallic glass sheet. 
     
     
         8 . The method according to  claim 1 , wherein steps a) and b) are conducted in air. 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         12 . The method according to  claim 1 , wherein the thermoplastic rolling step reduces perturbations in thickness that can grow in magnitude during the subsequent stretching step. 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . The method according to  claim 1 , wherein the bulk metallic glass feedstock comprises a plurality of bulk metallic glass pieces, wherein the plurality of bulk metallic glass pieces are joined in step b). 
     
     
         16 . The method according to  claim 15 , wherein the joining locations are controlled, wherein only portions of the bulk metallic glass pieces are joined. 
     
     
         17 . The method according to  claim 1 , wherein stretch rolling increases the bending ductility of the bulk metallic glass sheet. 
     
     
         18 . The method according to  claim 1 , further comprising the step of imposing a pattern on the bulk metallic glass sheet after step c). 
     
     
         19 . The method according to  claim 18 , wherein the pattern is imposed on the bulk metallic glass sheet by rolling the bulk metallic glass sheet through a set of patterned rollers, wherein the set of patterned rollers are maintained at a processing temperature of the bulk metallic glass sheet, wherein the rollers impose the pattern onto the bulk metallic glass sheet. 
     
     
         20 . The method according to  claim 18 , wherein after step c) a molding step is performed to impose the pattern onto the bulk metallic glass sheet. 
     
     
         21 . The method according to  claim 18 , wherein after step c) a molding step is performed to mold the bulk metallic glass sheet into a mold cavity. 
     
     
         22 . The method according to  claim 21 , wherein a shearing step is performed to cut the bulk metallic glass sheet into outlines set by the mold cavity. 
     
     
         23 . The method according to  claim 21 , wherein a deformation step is performed to corrugate the bulk metallic glass sheet into out of plane deformations set by the mold cavity. 
     
     
         24 . The method according to  claim 18 , wherein the pattern has a length scale of less than 1 mm. 
     
     
         25 . The method according to  claim 24 , wherein the pattern has a length scale of less than 0.5 mm. 
     
     
         26 . The method according to  claim 18 , wherein the pattern comprises mold cavities. 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . (canceled) 
     
     
         30 . (canceled) 
     
     
         31 . (canceled) 
     
     
         32 . A system for fabricating a bulk metallic glass sheet, the system comprising:
 a) a set of pre-heating plates, wherein the set of pre-heating plates are capable of sandwiching a bulk metallic glass feedstock therebetween to preheat the bulk metallic glass feedstock to a temperature sufficient to soften the bulk metallic glass feedstock but that does not significantly contribute to a consumed crystallization time of the bulk metallic glass;   b) a set of rotatable heated rollers maintained at a processing temperature of the bulk metallic glass, wherein as the set of heated rollers rotates, the heated rollers thermoplastically roll the bulk metallic glass feedstock received from the step of pre-heating plates therebetween to thin the bulk metallic glass feedstock into a bulk metallic glass sheet, wherein the set of heated rollers comprise a hard metal that is sufficiently strong at the processing temperature of the bulk metallic glass; and   c) a stretching mechanism capable of stretching the rolled bulk metallic glass sheet exiting the set of heated rollers under controlled velocity.   
     
     
         33 . The system according to  claim 32 , wherein the stretching mechanism moves along a negative temperature gradient. 
     
     
         34 . The system according to  claim 32 , wherein the stretching mechanism is controlled by velocity as it exits from the set of heated rollers. 
     
     
         35 . The system according to  claim 34 , wherein the stretching mechanism pulls the bulk metallic glass sheet at a faster rate than the bulk metallic glass proceeds through the set of heated rollers. 
     
     
         36 . The system according to  claim 34 , wherein the stretching mechanism comprises a set of rotatable cool rollers, wherein said set of rotatable cool rollers are maintained at a lower temperature than the set of heated rollers and receive the bulk metallic glass sheet therebetween as it exits from the set of heated rollers. 
     
     
         37 . The system according to  claim 34 , where in the stretching mechanism comprises a clamping device that receives the bulk metallic glass sheet therebetween as it exits from the set of heated rollers. 
     
     
         38 . The system according to  claim 36 , wherein the set of cool rollers rotate at a faster rate than the set of heated rollers. 
     
     
         39 . The system according to  claim 32 , further comprising a set of rotatable patterned rollers, wherein the patterned rollers impose a pattern onto the bulk metallic glass sheet after it exits the stretching mechanism. 
     
     
         40 . The system according to  claim 39 , wherein the set of patterned rollers are maintained at a processing temperature of the bulk metallic glass. 
     
     
         41 . (canceled) 
     
     
         42 . (canceled) 
     
     
         43 . (canceled) 
     
     
         44 . The system according to  claim 32  wherein the steps are performed in air. 
     
     
         45 . (canceled) 
     
     
         46 . (canceled)