Journal Article

Enhanced thermal stability of nanograined metals below a critical grain size

Lu, K., Li, X. Y., Zhou, X.

2018

Overview

Synthesizing metals with extremely small (nanoscale) grain sizes makes for much stronger materials. However, very small–grained materials start to coarsen at relatively low temperatures, wiping out their most desirable properties. Zhou et al. discovered a way to avoid this problem by mechanically grinding copper and nickel at liquid nitrogen temperatures. The processing method creates low-angle grain boundaries between the nanograins, which promotes thermal stability. Science , this issue p. 526 Low-temperature plastic deformation creates nanoscale metals more resilient to higher-temperature grain coarsening. The limitation of nanograined materials is their strong tendency to coarsen at elevated temperatures. As grain size decreases into the nanoscale, grain coarsening occurs at much lower temperatures, as low as ambient temperatures for some metals. We discovered that nanometer-sized grains in pure copper and nickel produced from plastic deformation at low temperatures exhibit notable thermal stability below a critical grain size. The instability temperature rises substantially at smaller grain sizes, and the nanograins remain stable even above the recrystallization temperatures of coarse grains. The inherent thermal stability of nanograins originates from an autonomous grain boundary evolution to low-energy states due to activation of partial dislocations in plastic deformation.

• Publisher: The American Association for the Advancement of Science
• Subject: Ambient temperature / Coarsening / Copper / Deformation / Dislocations / Grain boundaries / Grain size / Heavy metals / High temperature / Liquid nitrogen / Low temperature / Materials science / Nanomaterials / Nickel / Particle size / Plastic deformation / Recrystallization / Stability / Thermal stability