Forming of metallic glass by rapid capacitor discharge forging
A forging apparatus and method of uniformly heating, rheologically softening, and thermoplastically forming metallic glasses rapidly into a net shape using a rapid capacitor discharge forming (RCDF) tool are provided. The RCDF method utilizes the discharge of electrical energy stored in a capacitor to uniformly and rapidly heat a sample or charge of metallic glass alloy to a predetermined “process temperature” between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy in a time scale of several milliseconds or less. Once the sample is uniformly heated such that the entire sample block has a sufficiently low process viscosity it may be shaped into high quality amorphous bulk articles via forging in a time frame of less than 1 second.
1. A method of shaping an amorphous metal formed of an alloy comprising:
heating the entirety of the amorphous metal at a rate of at least 500 K/sec to a temperature between the glass transition temperature of the amorphous metal and the equilibrium melting point of the alloy;
applying a deformational force to the amorphous metal to shape the amorphous metal into an amorphous article; and
cooling said amorphous article to a temperature below the glass transition temperature of the amorphous metal.
2. The method of claim 1 , wherein the amorphous metal has a resistivity that does not increase with temperature.
3. The method of claim 1 , wherein the amorphous material has a relative change of resistivity per unit of temperature change (S) of no greater than about 1×10 −4 ° C. −1 and a resistivity at room temperature (po) between about 80 and 300 μΩ-cm.
4. The method of claim 1 , wherein the processing temperature is about halfway between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy.
5. The method of claim 1 , wherein the processing temperature is such that the viscosity of the heated amorphous material is from about 1 to 10 4 Pas-sec.
6. The method of claim 1 , wherein the amorphous material is an alloy based on an elemental metal selected from the group consisting of Zr, Pd, Pt, Au, Fe, Co, Ti, Al, Mg, Ni and Cu.
7. The method of claim 1 , wherein the said heating generates an electrical field in said amorphous metal, and wherein the electromagnetic skin depth of the dynamic electric field generated is large compared to the radius, width, thickness, and length of the charge.
8. The method of claim 1 , wherein the heating step occurs through at least two electrodes connected to opposite ends of said amorphous metal.
9. The method of claim 1 , wherein the heating and shaping of the amorphous metal are complete in a time of between about 100 μs to 1 s.