Lab profile: Yong Yang, City University of Hong Kong

Glass has been used by humans for centuries and is a mainstay of modern optical technologies. Metallic glasses are a relative newcomer to the family but attract significant attention because of their unique combination of strength, formability, corrosion resistance, biocompatibility, and conductivity.

Yong Yang has always been fascinated by metallic glasses and has spent his career developing materials with advanced properties and new methods of production. He received a BS in mechanics and economics from Peking University and an MPhil from HKUST prior to gaining a PhD in solid mechanics and materials science from Princeton University. He joined City University of Hong Kong in 2012, where he is now a professor in mechanical engineering. He was awarded the Sayre Graduate Prize and Wu Prize for Excellence at Princeton and the President’s Award from City University of Hong Kong in 2016.

Yong talked to Materials Today about his current research and future plans.

How long has your group been running?

I have been running the group for over seven years since I joined CityU in 2012.

How many staff currently makes up your group?

At the current moment, I have 12 group members, including three postdocs and nine PhD students.

What are the major themes of research in your group?

The major themes of my research include the development of advanced structural materials with superior properties using a multi-scale methodology involving both experimental and computational mechanics. At the current time, we are mainly focusing on bulk metallic glasses, high entropy alloys, and 2D metals.

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

I was attracted to this area because of the unique properties of metallic glasses and high entropy alloys. Unlike conventional crystalline metals, metallic glasses do not possess well-defined long-range structural order. Although their mechanical strength is very high, easily reaching 1-2 GPa at room temperature, their mechanical behavior is more akin to a viscous liquid (or a deeply frozen liquid). As a result, they can easily lose their strength under certain extreme conditions and start to flow. This could lead to many fascinating applications yet to be fully explored.

On the other hand, high-entropy alloys are compositionally complex alloys without base elements. On the fundamental level, it is believed that they have a frustrated or distorted crystalline structure because of the atomic size misfit of their components and chemical randomness. Consequently, high-entropy alloys exhibit many unusual properties that are not commonly seen in conventional crystals.

Recently, we have developed several methods to fabricate large-area 2D metals or metallic nanosheets, including 2D high-entropy alloys and 2D metallic glasses. This is a new and emerging research area in my group. 

What facilities and equipment does your lab have?

In our group, we have and have access to various kinds of facilities, from materials development to characterization and computation. These include conventional facilities for materials development, such as furnaces for arc-melting and melt spinning, magnetron sputtering and electron beam sputtering, as well as ex-situ and in-situ nanoindentation systems for nanomechanical characterization and various microscopes, such as scanning electron microscope, transmission electron microscope, focused ion beam and 3D atom probe.

Do you have a favorite piece of kit or equipment?

My favorite piece of equipment is our multi-functional nanoindentation system. It enables us to do nano-mechanical experiments on different materials at various temperatures, with or without an electric voltage.

What do you think has been your most influential work to date?

I think that my research on structural heterogeneity in metallic glasses and their applications, such as cold joining, should have the highest impact. I believe that cold joining of metallic glasses may open up a new way to solve long-standing problems in the field of metallic glasses, such as the issue of glass forming ability and lack of tensile ductility. At the fundamental level, cold joining of metallic glasses is related to fast dynamics, dynamic heterogeneity, and anelasticity in metallic glasses.

What is the key to running a successful group?

Aside from securing research funding and recruiting good and passionate students, we schedule weekly meetings so that each PhD student can present their research to me and talk about their progress and difficulties – with immediate feedback. I believe that discussion is key to the success of our group.

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

In years to come, we will develop our strength in low dimensional metallic glasses/high-entropy alloys through inter-institutional and international collaborations.

Key publications

1. J. Ma, C. Yang, X.D. Liu, B.S. Shang, Q.F. He, F.C. Li, T.Y. Wang, D. Wei, X. Liang, X.Y. Wu, Y.J. Wang, F. Gong, P.F. Guan, W.H. Wang, Y. Yang. Fast surface dynamics enabled cold joining of metallic glasses. Science Advances (2019), accepted.
2. J.C. Qiao, Q. Wang, J.M. Pelletier, H. Kato, R. Casalini, D. Crespo, E. Pineda, Y. Yao, Y. Yang. Structural heterogeneities and mechanical behavior of amorphous alloys. Progress in Materials Science 104 (2019) 250-329. https://doi.org/10.1016/j.pmatsci.2019.04.005
3. Y.C. Hu, Y.W. Li, Y. Yang, P.F. Guan, H.Y. Bai, W.H. Wang. Configuration correlation governs slow dynamics of supercooled metallic liquids. Proc.  Natl. Acad.  Sci. USA (PNAS) 115 (2018) 6375-6380. https://doi.org/10.1073/pnas.1802300115
4. Q. Wang, J.J. Liu, Y.F. Ye, T.T. Liu, S. Wang, C.T. Liu, J. Lu, Y. Yang. Universal secondary relaxation and unusual brittle to ductile transition in metallic glasses. Materials Today 20 (2017), 293-300.  https://doi.org/10.1016/j.mattod.2017.05.007
5. Y.F. Ye, Q. Wang, J. Lu, C.T. Liu, Y. Yang. High entropy alloys: Challenges and prospects. Materials Today 19 (2016) 349-362. https://doi.org/10.1016/j.mattod.2015.11.026
6. Q. Wang, S.T. Zhang, Y. Yang, C.T. Liu, Y.D. Dong, J. Lu. Unusual fast secondary relaxation in metallic glass. Nature Communications, 6 (2015) 7876. https://doi.org/10.1038/ncomms8876
7.  J.C. Ye, J. Lu, C.T. Liu, Q. Wang, Y. Yang. Atomistic Free-Volume Zones and Inelastic Deformation of Metallic Glasses. Nature Materials 9 (2010) 619-623. https://doi.org/10.1038/nmat2802