The Progress Report for CAS-Croucher Funding Scheme for Joint Laboratories On Study of Mechanical Properties of Advanced Materials with Nanotwins Overview of progress Since City University of Hong Kong (CityU) and Institute of Metal Research, Chinese Academy of Science (IMR-CAS) Joint Laboratory of Nanomaterials & Nanomechanics was set up in 2008, their collaboration has been developing. A joint research team was built up between IMR-CityU through a high level research project supported by CROUCHER Foundation in 2010. In order to develop a leading position in the nanotwinned materials preparation for structural applications with optimized mechanical behaviors, both teams from IMR and CityU have carried out a series of preliminary experiments for forming nanotwins in different metals through plastic deformation to understand the mechanism of the nucleation of nanotwin via experimental and numerical means and to look for the strength-ductility synergy. The main deliverables have been obtained as follow: • A modified version of SMAT machine has been built in CityU and IMR. A larger sample can be treated by the machines with rotational function, and the extraordinary intrinsic tensile plasticity in gradient nano-grained Cu was revealed; • New routes was developed for forming nanotwins in different metals and alloys (for example: Cu, 316 stainless steel etc.) through high speed or cryogenic dynamic plastic deformation, and for enhanciing the strength-ductility synergy by static rescrystallization of nanotwinned structures; • The relations of magnitude of strain rates and the mechanism of formation of nanotwins of a metal are revealed; • A quantitative mechanism-based plasticity model has been developed and used as a tool to enhance the overall strength and ductility of the materials through optimizing the thickness of the twin lamellae and grains microstructures; • A micromechanics-based model has been developed to optimize the microstructures and distribution of the grain sizes to achieve the ultimate goal of high strength and high ductility of polycrystalline metals. Key events In order to maintain an efficient communication between the Hong Kong team, IMR-CAS team, both the Hong Kong and IMR-CAS teams have joined annual meeting of CAS-Croucher Funding Scheme for Joint Lab with academic exchanges. The details are listed as follow: 1. 2010 Annual Meeting of CAS-Croucher Funding Scheme for Joint Lab was held at 19-21 Nov in Shenzhen. 2. 2011 Annual Meeting of CAS-Croucher Funding Scheme for Joint Lab was held at 27-30 Nov in Hong Kong. Grant applications Prof. K. LU and Prof. J. LU have led several top research teams including IMRCAS, several universities, and industrial parties in China to apply a joint-research project of National Key Scientific Research by Ministry of Science and Technology of China (MOST) on Research on fabrication of multi-scale hierarchical nanostructured metallic materials and its exceptional properties in 2011. The project is granted successfully. The kickoff meeting of this project was held in February 2012 in Shenzhen. Awards The study on revealing extraordinary intrinsic tensile plasticity in gradient nanograined copper was selected as one of the Top Ten Progresses of China Science in 2011. Publications In this period sixteen papers have been published related to this project including one published in Science and seven in Acta Materialia. • H.L. Chan, H.H. Ruan, A.Y. Chen, J. Lu, Optimization of strain-rate to achieve exceptional mechanical properties of 304 stainless steel using high speed ultrasonic SMAT. Acta Materialia, 58(2010)5086-5096. • Y.D. Wang, W.J. Liu, L. Lu, Y. Ren, Z.H. Nie, J. Almer, S. Cheng, Y.F. Shen, L.A. Zuo, P.K. Liaw, K. Lu, Low temperature deformation detwinning-a reverse mode of twinning. Advanced Engineering Materials, 12(2010)906-911. • L. Lu, K. Lu, Metallic materials with nano-scale twins. Acta Metallurgica Sinica, 46(2010)1422-1427. • Y.T. Zhu, R.Z. Valiev, T.G. Langdon, N. Tsuji, K. Lu, Processing of nanostructured metals and alloys via plastic deformation. MRS Bulletin, 35(2010) 977-981. • X.H. Chen, L. Lu, K. Lu, Grain size dependence of tensile properties in ultrafinegrained Cu with nanoscale twins. Scripta Materialia, 64(2011)311-314. • H.L. Wang, Z.B. Wang, K. Lu, Interfacial diffusion in a nanostructured Cu produced by means of dynamic plastic deformation. Acta Materialia, 59(2011) 1818-1828. • T. H. Fang, W. L. Li, N. R. Tao, K. Lu, Revealing extraordinary intrinsic tensile plasticity in gradient nano-grained copper. Science, 331(2011)1587-1590. • L.M. Wang, Z.B. Wang, K. Lu, Grain size effects on the austenitization process in a nanostructured ferritic steel. Acta Materialia, 59(2011)3710-3719. • A.Y. Chen, H.H. Ruan, J. Wang, H.L. Chan, Q. Wang, Q. Li, J. Lu, The influence of strain rate on the microstructure transition of 304 stainless steel. Acta Materialia, 59(2011)3697-3709. • Z.B. Wang, K. Lu, G. Wilde, S.V. Divinski, Effects of grain growth on interface diffusion in nanostructured Cu. Scripta Materialia, 64(2011)1055-1058. • G.H. Xiao, N.R. Tao, K. Lu, Strength-ductility combination of nanostructured CuZn alloy with nanotwin bundles. Scripta Materialia, 65(2011)119-122. • L.L. Zhu, H.L. Ruan, X.Y. Li, M. Dao, H.J. Gao, J. Lu, Modeling grain size dependent optimal twin spacing for achieving ultimate high strength and related high ductility in nanotwinned metals. Acta Materialia, 59(2011)5544-5557. • B. Yao, Z. Han, Y.S. Li, N.R. Tao, K. Lu. Dry sliding tribological properties of nanostrucured copper subjected to dynamic plastic deformation. Wear, 271(2011)1609-1616. • L.L. Zhu, J. Lu, Modeling the plastic deformation of nanostructured metals with bimodal grain size distribution. International Journal of Plasticity, 3031(2012)166-184. • H.L. Wang, Z.B. Wang, K. Lu. Enhanced reactive diffusion of Zn in a nanostructured Fe producedby means of surface mechanical attrition treatment. Acta Materialia, 60 (2012)1762-1770. • L.M. Wang, Z.B. Wangy, S. Guo, K. Lu, Annealing-induced grain refinement in a nanostructured ferritic steel. Journal Materials Science & Technology, 28(2012)41-45. • F.K. Yan, G.Z. Liu, N.R. Tao, K. Lu, Strength and ductility of 316L austenitic stainless steel strengthen by nano-salce twin bundles. Acta Materialia, 60(2012)1059-1071.