Smaller and stronger: the power of nano-crystalline structures
Professors J. Lu and K. Lu have been research partners in collaboration since 1997 with support from the National Natural Science Funding of China, long before the Joint Laboratory of Nanomaterials and Nanomechanics was set up in 2008 between the Polytechnic University of Hong Kong (PolyU) and the Institute of Metal Research at the Chinese Academy of Science (IMR-CAS). As J. Lu moved to the City University of Hong Kong (CityU) in 2010, a joint research team was set up between IMR-CityU through a high-level research project supported by the Croucher Foundation (CAS-Croucher Funding Scheme).
Nano-grained metals have been known to be brittle and thermally unstable. “Our main objective is to achieve strain delocalisation and strain-hardening to increase tensile strength without compromising ductility,” K. Lu explained. “We published our first paper together in 1999 on surface nano-crystallisation of metallic materials by a novel method named surface mechanical attrition treatment,” he described. “Then, in 2008, we reported another novel technique called surface mechanical grinding treatment, which reduces the surface roughness of metallic materials.” More work followed and in 2011, they introduced the idea of tension-induced softening and hardening of grains in the same sample simultaneously. Just this year, their latest findings include enhancement of fatigue resistance by phase-gradient nanostructure modification of metallic surfaces.
Their current joint-laboratory continues to work on these novel metallic surface processing techniques to alter metal and alloy surfaces into nanocrystalline structures with better strength and enhanced physical properties like greater ductility so they do not break easily when deformed, for example. They develop the techniques and apply them to different materials, such as copper, iron, and chromium. Their latest research aim is to develop the ideal architecture of gradient nanostructures.
Materials with such nano-crystalline structures on their surfaces can be used in the automotive industry, on aeroplane engines, and even in the nuclear industry. Currently, Baosteel and other steel manufacturers are using their novel concepts and techniques, and further developing them for industrial purposes. For example, steel with a nano-crystalline surface is currently used in rollers of heavy machinery due to its wear resistant properties.
J. Lu and K. Lu told us during an interview, “We are very productive research collaborators in that we have the largest number of collaborated joint publications inside of our respective publication lists, have regular meetings, and around 40 joint publications so far!” They hope that their research will expand to include more industry involvement and have biomedical and aerospace applications in the near future.
J. Lu is currently the vice-president (Research and Technology) and the dean of Graduate Study at CityU, while K. Lu is a professor at Shenyang National Laboratory for Materials Science, IMR-CAS. Their study on revealing extraordinary intrinsic tensile plasticity in gradient nano-grained copper was selected as one of the Top Ten Progresses of China Science in 2011.
In this period, 13 papers have been published related to this CAS-Croucher joint project.
For more information about CAS-Croucher Joint Laboratories, please click here.