Abstract:
Twinning-induced plasticity (TWIP) steels have excellent combination of strength and ductility and are potential lightweight materials for automotive applications. Understanding the twinning mechanisms in TWIP steels is essential for the successful application of TWIP steels in automotive industry. The first part of this work is to employ sub-micon and micron-sized single crystalline pillars to investigate the nucleation and growth mechanism of deformation twins. It is found that the nucleation and growth of deformation twins are due to emission and glide of successive partial dislocations. The twin thickness can range from nanometres to micrometres. A physical model is proposed to simulate the nucleation and growth of deformation twins and the model predictions agree well with experimental observations. The second part of this work investigates the deformation mechanism of bulk samples in TWIP steels. Deformation mechanism at high strain rates were investigated. By synchrotron X-ray diffraction experiments, the present work demonstrates that a higher strain rate leads to a lower dislocation density and a lower twinning probability, which is opposite to other fcc metals. Furthermore, it has been demonstrated in our latest works that the contribution of twins to the flow stress is limited.
Instead, dislocations, via forest hardening, account for up to ~90% of the flow stress increment after yielding in the present TWIP steel. In other words, the contribution of twins to the work-hardening rate and flow stress of TWIP steels may have been overestimated in the literature.

Short Bio:
Dr. Huang received his BEng and MPhil in Mechanics from Shanghai Jiao Tong University (SJTU) in 2002 and 2004, respectively, and his PhD in Materials Science in 2008 from Delft University of Technology (TU Delft), The Netherlands. From 2008 to 2010, he worked as a research engineer at ArcelorMittal (the largest steel company in the world) in Maizieres-les-Metz, France. His research work in ArcelorMittal focused on the development of new advanced steels for automotive applications. Dr. Huang joined University of Hong Kong in 2010 as an Assistant Professor. Dr. Huang’s research interests focus on two areas: (1) fundamentals of microstructure-property relationship and phase transformation of advanced steels, and (2) development of lightweight materials for automotive applications. Both experimental and modelling works are involved in his research. His research projects have been well funded by external funding bodies such as General Research Fund, Innovation and Technology Fund, National Science Foundation of China, and industries from Europe and China (e.g. ArcelorMittal France, General Motors, Ansteel). Dr. Huang is an editorial board member of Materials Science and Technology and the Key Reader for Metallurgical and Materials Transactions A. Dr. Huang has given invited talks in international conference such as PTM 2015, THERMEC, and MRS. Dr. Huang has published 50+ SCI papers in international journals such as Acta Materialia, Scripta Materialia, Journal of Mechanics and Physics of Solids, etc., and has an H-Index of 14.