Thermo-mechanical Process for Enhanced Quality of Grain Boundary Networks in High-purity Metals

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Thermo-mechanical process to enhance the quality of grain boundary networks
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Inventors
Professor Christopher Schuh
Department of Materials Science and Engineering, MIT
External Link (schuh.mit.edu)
Koichi Kita
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Thermo-mechanical process to enhance the quality of grain boundary networks

US Patent 8,876,990
Publications
The Hall–Petch breakdown at high strain rates: Optimizing nanocrystalline grain size for impact applications
Applied Physics Letters, Vol. 93, Issue 17, 1916 (2008)
Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys
Physical Review B, Vol. 79, 094112 – Published 24 March 2009

Applications

The thermo-mechanical process can be applied to high-purity metals including various kinds of face centered cubic (FCC) metals such as pure copper, other copper alloys, brass, pure nickel, nickel alloys and various kinds of austenitic stainless steels. This technique would be of benefit to tool manufacturing and materials development. 

Problem Addressed

One important cause of non-uniform dissolution is thought to be the non-uniformity of grain boundaries in metal anodes. Metal anodes are typically used for electroplating due to one of their most important properties: the uniformity of dissolution. Grain boundaries are less chemically stable than the interior regions of crystal grains, so grain boundaries are preferentially dissolved during the electroplating process. There is a certain kind of grain boundaries often called "special" grain boundaries that show much better properties than others.  By increasing the fraction of "special" grain boundaries in copper metal anodes though Grain Boundary Engineering (GBE), it is expected to be effective in reducing non-uniform solution. However, the most effective GBE technologies reported to date involve many cycles of cold work/hot annealing, which would be especially inefficient in practice at large scales.

Technology

This invention is a new method to change the internal structure of metals through a process of deformation and annealing. It pertains to changing the crystallographic types of grain boundaries to increase the fraction of “special” grain boundaries and to tailor desirable physical and chemical properties in metals. Instead of running cycles of "deformation at ambient temperature" and "annealing at apparently higher temperature than ambient temperature", the new isothermal thermo-mechanical process can help avoid time and energy-consuming heating and cooling steps.

Advantages

  • More effective that previously known grain boundary engineering (GBE) processes
  • Avoids the energy-consuming steps of heating and cooling the system
  • Applicable to various kinds of FCC metals, not just pure copper
  • More suitable for practical manufacturing application