DEPSCOR RESEARCH COLLABORATION FY21 TAILORING FRACTURE PERFORMANCE THROUGH HIERARCHICAL POROSITY IN TI
Abstract
The objective of this project is to understand how hierarchical porosity controls deformation induced martensitic phase transformations – and consequently affects fracture toughness – of Titanium (Ti). In Ti, the beta-to-alpha phase transformation (in which the body centered cubic (bcc) beta phase transforms to the hexagonal close packed (hcp) alpha phase) has significant influence on fracture toughness and can occur through a solid-state deformation-induced martensitic transformation. Nanopores can act as stress concentrators to activate these deformation-induced martensitic transformations at lower externally-applied stresses and strains. Researchers have engineered porosity into Ti and Ti alloys for defense applications requiring light weighting and impact tolerance, but current techniques produce microscale pores that are unlikely to fundamentally alter underlying deformation mechanisms. Herein, we couple nanoscale and microscale pores to synergistically tailor strength and deformation mechanisms, respectively, creating hierarchical porosity-enabled martensitic transformations for tailored fracture toughness. Our overarching hypothesis is that nanopores will concentrate stress to trigger deformation induced phase transformations, and when coupled with microscale pores, can enable tailored, position sensitive fracture behavior. Our approach couples phase field modeling with materials synthesis and characterization in a closed-loop project design that will sequentially iterate on nanopore volume fraction and starting phase fractions. Ti specimens will be synthesized using a magnesiothermic or calciothermic reaction to control pore sizes across length scales for engineered hierarchical porosity. Deformation microstructures at pores will be characterized through in situ x-ray tomography and transmission electron microscopy. The scientific outcome is a mechanistic understanding of porosity-enabled, deformation-induced phase transformations, which can be used to design Ti alloys having enhancing fracture toughness. The impact will be a novel paradigm for porosity engineering of lightweight materials to tune the phase transformability at the nano/microscale, enabling position-sensitive tailoring of mechanical and fracture properties. This project is relevant to the Department of Defense (DoD) Solid Mechanics Program.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 20, 2023
- Source ID
- FA95502210450
Entities
People
- Janelle Wharry
Organizations
- Air Force Office of Scientific Research
- Office of the Secretary of Defense