PT  - JOURNAL ARTICLE
AU  - Zhou, X.
AU  - Li, X. Y.
AU  - Lu, K.
TI  - Enhanced thermal stability of nanograined metals below a critical grain size
AID  - 10.1126/science.aar6941
DP  - 2018 May 04
TA  - Science
PG  - 526--530
VI  - 360
IP  - 6388
4099  - http://science.sciencemag.org/content/360/6388/526.short
4100  - http://science.sciencemag.org/content/360/6388/526.full
SO  - Science2018 May 04; 360
AB  - 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. 526The 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.