Prof. Yong Liu, is the Director of Powder Metallurgy Research Institute of Central South University. He got his Ph.D. degree of Materials Science in the same institute in 1999, and then, has been working there for more than 20 years. He also was a visiting scientist in Oak Ridge National Laboratory during 2005-2006, and in RWTH Aachen University during 2009-2011. His research field covers high temperature structural materials, titanium alloys and hard materials, usually through the technique route of powder metallurgy. He has won many academic honors, including Alexander von Humboldt Fellowship, and National S&T Award of China, published more than 100 peer-reviewed papers in various journals, and also more than 50 patents. He is now serving as editors for such journals as Intermetallics and Materials Characterization.
Metal-metal composite (MMC) is a typical heterogeneous material that consists of metal matrix and secondary metallic phase. Due to the compositional gradient interface, MMCs usually have a better combination of strength and ductility compared with conventional ceramic reinforced composites. However, the effecting mechanism of gradient interface on mechanical behavior of MMCs is still unclear. In this study, we proposed a powder metallurgical method to prepare titanium matrix MMCs, such as Ti-Ta, Ti-Mo and Ti-W composites. A superior combination of tensile strength (1200~1500 MPa) and elongation (8~20%) was achieved. It was found that the structural gradient interface, produced by the compositional gradient, could generate strong hetero-deformation induced (HDI) stress, which consequently enhanced the strength of the MMCs. Meanwhile, multiple deformation modes including dislocation planar sliding, stress-induced twining (TWIP), and stress-induced martensite phase transformation (TRIP) were activated around the gradient interface during plastic deformation, which help to release stress concentration and increase strain hardening capability, thereby resulting in a good ductility. Moreover，the mechanical Behavior of Ti-metal composites under high strain rates were also reported. Besides, we have proposed a new interface stress model to evaluate the HDI stress from the perspective of residual strain energy. The HDI stress values obtained from the new interface stress model can more reasonably explain the interfacial strengthening effects than those from the well-used back stress model for heterogeneous-structured materials.
Keywords: Metal-metal composites; Strengthening mechanis; Interfacial stress model