Metals get stronger as their grain size is reduced. This behavior, described by the Hall-Petch relation, is exemplified by nanocrystalline metals. Their exceptionally small grains give them extraordinary strength, but there are drawbacks. Among these are the difficulty in achieving a nanoscale grain size and maintaining it during processing. The smaller the grain size, the more favorable it is for the grains to coalesce and grow. The grains can be “stabilized” at a small size by adding a second element or second phase. The secondary addition will either reduce the driving force for grain growth (thermodynamic stabilization) or will physically hinder the grain growth (kinetic stabilization). There are specific parameters required of the solute(s) added to the metal. Often these are elements or compounds that are significantly different in size or stable at high temperature. Two examples are zirconium or tungsten added to copper. Zirconium atoms are much larger than copper atoms and they segregate to grain boundaries and reduce the driving force for growth. Tungsten, on the other hand, exists in the form of discrete particles which pin the grain boundaries from moving. Images of these materials are below (click on images for full resolution).
Related publications are listed below (for full list, see Publications).
Publications on Nanocrystalline Metals and Alloys:
- Vincent H. Hammond, Mark A. Atwater, Kristopher A. Darling, Hoang Q. Nguyen, Laszlo J. Kecskes. Equal-Channel Angular Extrusion of a Low-Density High-Entropy Alloy Produced by High-Energy Cryogenic Mechanical Alloying. JOM; 66 (10), pp. 2021-2029 (2014)
- K.A. Darling, M.A. Tschopp, B.K. VanLeeuwen, M.A. Atwater, Z. K. Liu. Mitigating grain growth in binary nanocrystalline alloys through solute selection based on thermodynamic stability maps. Computational Materials Science; 84 pp. 255-266 (2014)
- D Roy, BV Mahesh, MA Atwater, TE Chan, RO Scattergood, CC Koch. Grain size stability and hardness in nanocrystalline Cu–Al–Zr and Cu–Al–Y alloys. Materials Science and Engineering: A; 598 pp. 217-223 (2014)
- Mark A Atwater, Suhrit Mula, Ronald Scattergood, Carl C. Koch. Thermal Stability of Nanocrystalline Copper Alloyed with Antimony. Metallurgical and Materials Transactions A; 44 (12) pp. 5611-5616 (2013)
- Kris Darling, Laszlo Kecskes, Mark Atwater, John Semones, Carl Koch, Ronald Scattergood. Thermal Stability of Nanocrystalline Nickel with Yttrium Additions. Journal of Materials Research; 28 pp. 1813-1819 (2013)
- D. Roy, M. A. Atwater, R. O. Scattergood, C. C. Koch. Studies on thermal stability, mechanical and electrical properties of nanocrystalline Cu99.5Zr0.5 alloy. Journal of Alloys and Compounds. Journal of Alloys and Compounds; 558 pp. 44–49 (2013)
- Mark A. Atwater, Hamed Bahmanpour, Ronald O. Scattergood and Carl C. Koch. The thermal stability of nanocrystalline cartridge brass and the effect of zirconium additions. Journal of Materials Science; 48 pp. 220-226 (2013)
- M. A. Atwater, R. O. Scattergood, C. C. Koch. The stabilization of nanocrystalline copper by zirconium. Materials Science and Engineering: A; 559 pp. 250–256 (2013)
- Mark A. Atwater, Debdas Roy, Kristopher A. Darling, Brady G. Butler, Ronald O. Scattergood, and Carl C. Koch. The thermal stability of nanocrystalline copper cryogenically milled with tungsten. Materials Science and Engineering: A; 558 pp. 226–233 (2012)
- Mark A. Atwater, Kris A. Darling. A Visual Library of Stability in Binary Metallic Systems: The Stabilization of Nanocrystalline Grain Size by Solute Addition: Part 1. U.S. Army Research Laboratory Technical Report; pp. 1-70 (2012)
- Hamed Bahmanpour, Khaled M Youssef, Jelena Horky, Daria Setman, Mark A Atwater, Michael J Zehetbauer, Ronald O Scattergood, Carl C Koch. Deformation twins and related softening behavior in nanocrystalline Cu-30%Zn alloy. Acta Materialia; 60(8) pp. 3340–3349 (2012)
- S. Mula, H. Bahmanpour, M. Atwater, W. Jian, R. O. Scattergood, C. C. Koch. Thermodynamic feasibility of solid solubility extension of Nb in Cu and their thermal stability. Materials Science and Engineering: A; 539 pp. 330-336 (2012)