Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.

http://dx.doi.org/10.1073/pnas.1517193112

The authors thank Prof. W. D. Nix for his insightful and constructive comments on this paper. X. W., M. Y., F. Y., and Y. W. are funded by the National Natural Science Foundation of China (11572328, 11072243, 11222224, 11472286, and 51471039) and Ministry of Science and Technology (2012CB932203, 2012CB937500, and 6138504). Y. Z. is funded by the US Army Research Office (W911 NF-12-1-0009), the US National Science Foundation (DMT-1104667), and the Nanjing University of Science and Technology.

Wu XL,Yang MX,Yuan FP,et al. Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility[J]. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA,2015,112(47):14501-14505.