Metallic glasses are metals with the disordered atomic structure of glass. To shape a metallic glass, it must be heated then cooled without it crystallizing. Crystallization can occur if the sample is heated too slowly.
William Johnson and colleagues, California Institute of Technology, USA, have found a way to heat a metallic glass faster than crystallization can occur. They use ohmic heating — applying a current to the metallic glass to heat it uniformly at rates of ~106 K/s, well above the critical heating rate of ~200 K/s.
Using this method, the team could apply an injection molding technique to a bulk metallic glass using molding conditions typical to plastic. They could heat and mold a metallic glass rod into a toroid that was free of defects within 30 ms. This enables the use of cheaper and quicker processing which could see metallic glasses used in applications from cell phones to aircraft parts.
- Beating Crystallization in Glass-Forming Metals by Millisecond Heating and Processing
W. L. Johnson, G. Kaltenboeck, M. D. Demetriou, J. P. Schramm, X. Liu, K. Samwer, C. P. Kim, D. C. Hofmann,
Science 2011, 332(6031), 828-833.