Strong and ductile martensite induced by periodic solute segregation at variant boundary in an additively manufactured Ti-Cu alloy

Guest Speaker： Senior Lecteurer QIU Dong, RMIT University 

Inviter: Assoc. Prof. Li Yangxin

Date&Time: Monday  1. Apr. 14:00-15:00

Venue: Yiucheng Lecture Hall (500), Xu Zuyao Building

Biography:

Dr Qiu was awarded a Ph.D degree majored in materials science and engineering from Tsinghua University in 2005. He had been working as a Postdoctoral Research Fellow, and then Australian Research Fellow at the University of Queensland from 2005 to 2014. Dr Qiu joined RMIT University in 2015 as a Vice Chancellor’s Senior Research Fellow. In the last 10 years, his research has spanned a range of areas, such as grain refinement of cast metals, crystallography in solid-solid phase transformations and surface modification of biomedical implants. His contribution to the research community is witnessed by 98 peer-reviewed journal papers, with 1 out of those published in Nature, 3 published in Nature Communications, 17 published in Acta Materialia, the leading journal in the field of physical metallurgy worldwide. His publications have been cited by more than 4500 times and his H-index is 37 in Scopus. He has also succeeded in obtaining fund of 5 Australian Research Council (ARC) Discovery Projects and 1 ARC Linkage Project. Dr Qiu is currently appointed as a Key Reader of ‘Metallurgical and Materials Transaction A’ and an ARC Assessor. His current research interest includes microstructure manipulation of additively manufactured (AM) metal components and new alloy development through AM.

Abstract:

The fusion based metal additive manufacturing process, in particular laser powder bed fusion (L-PBF), revolutionizes the titanium industry due to its lower cost, shorter lead time and higher level of design flexibility. However, the most common product in the as-fabricated Ti alloys is martensite due to the high cooling rate, which is typically strong but intrinsically brittle. Herein we propose a new alloy design strategy to solve this dilemma by stimulating high density of inter-variants transformation twins in an L-PBF Ti-5Cu alloy. The as-fabricated Ti-5Cu alloy comprises full martensite with a tensile strength of 1130 MPa and a fracture strain as high as 15%. Such excellent synergy of strength and ductility stems from the periodic segregation of solute Cu atoms on the inter-variant twin boundaries, which stabilizes thermodynamically the twin boundaries. Meanwhile, the fast diffusion of Cu atoms in Ti lattice facilitates such segregation is accomplished in a transient temperature field of the L-PBF process, without the need of any post-fabrication heat treatment. This manufacture-friendly, high-strength and high-ductility, martensitic alloy is expected to be a promising candidate for aerospace and biomedical applications.