Processing Heterogeneous Lamella fcc Alloys for Unprecedented High Strength and Ductility
Abstract
It is well known that there exists a "banana" curve for the strength and ductility of metals and alloys, where a material is either strong or ductile, but rarely both at the same time. Both high strength and high ductility are desired for structural applications. Recently, we found that Ti with heterogeneous lamella (HL) structure can be made to possess both high strength and high ductility, avoiding the curse of the "banana curve". In the HL structure, the soft large-grained lamellae are surrounded by hard ultrafine-grained hard matrix, which is opposite to the conventional microstructure. Importantly, the addition of the soft lamella to the ultrafine-grained hard matrix did not lower the global strength, which is against the principle that we know from textbook and literature. Furthermore this unique structure has even higher strain hardening rate than coarse-grained Ti, which is again extraordinary. This high strain hardening ensured its high ductility. If this discovery can be applied to other metals and alloys, it has the potential to revolutionize the structural metals and alloys industry and related applications. It should be noted that the HL structure is very different from the conventional "bi-modal" structure. The HL structure has high density of lamella interfaces, which is a critical requirement for superior properties. Ti used in the early study has a hexagonal close-packed (hcp) crystal structure, which has specific deformation texture and other characteristics from rolling. It is therefore important to study if metals and alloys with other crystal structures (e.g. fcc) can also be processed to produce HL structure and superior properties. In this proposed Short Term Innovative Research (STIR) project, I propose to investigate if HL structure can also be formed in fcc metals to produce a superior combination strength and ductility. Metals with fcc crystal structure have abundant slip systems, and should deform very differently from hcp Ti. Nevertheless, it is my hypothesis that similar structure and properties can be produced in fcc metals and alloys. The objective of this research is threefold: 1) to verify the feasibility of producing HL structures in fcc metals, 2) to probe fundamental science on how the HL structures are affected by processing parameters, and 3) to produce a combination of strength and ductility that is not accessible to corresponding conventional homogeneous fcc metals
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1710350
Entities
People
- Yuntain Zhu
Organizations
- Army Contracting Command
- North Carolina State University
- United States Army