Lab profile: Ke Lu, Institute of Metal Research, CAS

Introducing nanostructure into materials like metals can produce surprising results. Making the grain size smaller in some metals such as copper can increase strength. Other material properties like conductivity, ductility, and melting point can also be affected by the nanostructure.

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Ke Lu wants to understand the mechanisms underlying these findings and develop ways of nanostructuring materials to control their properties. He has created a research group at the Shenyang National Laboratory for Materials Science (SYNL) to explore these questions and provide potential answers for real-world applications. The Institute of Metal Research (IMR) in Shenyang, which is part of the Chinese Academy of Sciences (CAS), is home to Lu’s Nanometals Group.

Ke Lu talked to Materials Today about his research and plans for the future…

How long has your team been running?

The group was established in April 1993 after I returned from a postdoc at the Max Planck Institute for Metals Research in Stuttgart, Germany. I was appointed a full professor at IMR at that time.

How many staff makes up your team?

The size of my group has varied over the years. Currently, it is at its largest, consisting of 11 research associates, three technicians, and a secretary. In addition, we have 27 graduate students working towards their PhDs.

What are the major themes of research in your lab?

As the name suggests, my group concentrates on experimental studies on nanostructured metals and alloys. Our major themes of research include the development of new processing techniques for producing novel nanostructures in metals, stabilization of nanostructures in metals in terms of the hierarchical architecture of interfaces, and mechanical behaviors of nanostructured metals. The ultimate aim of our research is to develop nanostructured metals with novel properties and performance and to drive their usage in industrial applications. 

How and why did you come to work in these areas?

As early as the 1980s, nanostructured materials (mainly metals at that time) came to our attention because they exhibit some unique properties, such as extremely high hardness and strength, greatly enhanced diffusivity, etc. These are very attractive attributes for structural materials where mechanical properties are primary concerns. More interestingly, the property enhancements found in nanostructured materials are not induced by traditional alloying. Instead, properties are elevated within a very wide range without changing the chemical composition of the materials. Our work provides a new approach to developing materials with structure modifications on the nanometer scale, in addition to the traditional alloying. As property enhancements are induced without changing chemical constitutions, this approach is less resource dependent. I believe this a promising way to drive materials development sustainably.

What has been your highest impact/most influential work to date?

I think there are two pieces of our work that have had the most impact.

Firstly, the discovery of a nano-twinned structure in Cu has proved very important. The introduction of nano-twins in Cu significantly strengthens the metal without compromising its ductility and electrical conductivity [8]. The interactions between dislocations and twin boundaries at the nanometer scale enables nano-twins to effectively strengthen materials while keeping considerable ductility [6]. Nano-twinned structures also exhibit excellent thermal stability because of their low excess energy [1]. These features have helped advance different classes of materials including superalloys, ceramics, diamond, as well as interconnect metals.  

Secondly, I believe our development of surface nanocrystallization techniques and the discovery of the gradient nanostructures effect on mechanical properties in metals has been significant. In metals with a gradient nanostructured surface layer, the strength-ductility synergy is greatly enhanced because strain localization is effectively suppressed [3, 5]. Gradient nanostructured surface layers can elevate the fatigue strength and fatigue life of various engineering metals and alloys significantly. In addition, gradient nanostructures can lower the dry friction coefficients of Cu alloys considerably with much reduced wear rates [2].

What facilities and equipment does your lab have?

We have some facilities and equipment specially developed for processing nanostructured materials. They include different types of surface nanocrystallization techniques for metals and alloys, such as surface mechanical attrition treatment (SMAT), surface mechanical grinding treatment (SMGT), and surface mechanical rolling treatment (SMRT). There are also some facilities for processing bulk specimens of nanostructured metals, including dynamic plastic deformation (DPD) facilities in which strain rates as high as 1000 per second can be achieved, pulsed and DC electrodeposition facilities for producing nano-twinned and nanograined metals. Microstructural, compositional, and property (mechanical, physical, chemical) characterization of the nanometals we produce can be performed in the common facilities provided by SYNL and IMR. 

Do you have a favourite piece of kit or equipment?

We are proud of our facilities for surface nanocrystallization techniques (SMAT, SMGT, SMRT) of metals and alloys that were developed by my group over the past decades. These facilities have proven to be very powerful for producing thick gradient nanostructured surface layers (thickness on the millimeter scale) in various metals and alloys. Such gradient nanostructures, which are elastically homogeneous but plastically graded, offer a unique architecture to enable strain delocalization which is effective in enhancing strength-ductility synergy and related performance aspects of materials such as fatigue, friction and wear, and corrosion. It also provides a unique way of systematically studying grain refinement mechanisms at the nanometer scale and the size-dependence of various metal properties.

What is the key to running a successful lab?

To run a successful group, you have to have a long-term visionary target for research with your own identity. Both persistence and creativity are needed for doing original research, which is the soul of a successful group.

How do you plan to develop your lab in the future?

I will run the group, as best as I can, towards our ultimate goal of novel nanostructured metals for industrial applications. To do this, we have to keep doing original research with more focused themes, especially on intrinsic nano-size effects on material properties. Meanwhile, I will reinforce my group to face upcoming challenges by recruiting more young talent from different backgrounds in the future. 

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Key publications

1. K. Lu. Stabilizing nanostructures in metals using grain and twin boundary architectures. Nature Review Materials, 1 (2016) 16019.
2. X. Chen, Z. Han, X.Y. Li, K. Lu. Lowering coefficient of friction in Cu alloys with stable gradient nanostructures. Science Advances, 2 (2016) e1601942.
3. K. Lu. Making strong nanomaterials ductile with gradients. Science, 345 (2014) 1455.
4. X.C. Liu, H.W. Zhang, K. Lu. Strain-induced ultrahard and ultrastable nanolaminated structure in nickel. Science, 342 (2013) 337.
5. 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.
6. K. Lu, L. Lu, S. Suresh. Strengthening materials by engineering coherent internal boundaries at the nano-scale. Science, 324 (2009) 349.
7. Q.S. Mei, K. Lu. Melting and superheating of crystalline solids: From bulk to nanocrystals. Progress in Materials Science, 52 (2007) 1175.
8. L. Lu, Y.F. Shen, X.H. Chen, L.H. Qian, K. Lu. Ultrahigh strength and high electrical conductivity in copper. Science, 304 (2004) 422.