Fundamental Investigations of Impurity Effects in Titanium
Abstract
Funds are provided to investigate and model the effects of oxygen, aluminum, and other alloying elements on the deformation behavior of titanium. Titanium alloys are an attractive class of materials for a range of naval applications, owing to their excellent corrosion resistance, high strength, light weight, and formability. Despite this desirable combination of properties, the application of titanium-based materials in the Navy has been limited to date by their relatively high cost. To address this issue, research efforts are currently targeting the development of new processing and manufacturing methods, and the design of new marine grade alloys. In these efforts, a critical issue is the pronounced variation in the mechanical properties of titanium arising from small changes in the concentration of interstitial impurities, including in particular oxygen. The research in this program targets fundamental understanding of the origins of the effects of interstitial oxygen solute atoms on the mechanical behavior of hexagonal close-packed (hcp) alpha-Ti. In this work we exploit recent advances in in situ mechanical testing and high-speed diffraction imaging in the transmission electron microscope, coupled with computational approaches for predicting chemical effects on mechanical behavior based on the modern framework of density-functional-theory calculations. Through this integrated computational and experimental approach, the work in this program aims to elucidate the fundamental atomic-scale mechanisms underlying the effect of oxygen interstitials on the mechanical behavior of pure alpha-titanium, and the ways they can be influenced by controlled additions of substitutional solutes and related heat treatments. Specifically, this work focuses on understanding the effect of solute atoms on dislocation slip and deformation twinning. In the studies of dislocation slip we build upon recent observations suggesting that the pronounced effects of interstitial solutes on dislocation mobilities and deformation microstructures are linked to the intrinsic properties of dislocation cores in pure alpha-Ti, which feature a non-planar structure that is strongly affected by the presence of interstitial impurities. Similarly, the origins of the pronounced effects of oxygen impurities on twinning have been linked to the rate of diffusion of oxygen away from advancing twins. The present proposal will expand earlier studies to clarify the effects of strong solute interactions on the evolution of dislocation structures and the nucleation and growth of deformation twins. Through a systematic experimental study of slip and twinning deformation processes in samples with controlled solute and oxygen contents in the Ti-Al-O system, complemented by computational modeling targeting investigations of underlying mechanisms and deformation dynamics, we will seek to understand the synergistic effects that substitutional and interstitial solutes can have in governing deformation processes in alpha-Ti. It is anticipated that the fundamental insights derived from this work will provide an expanded scientific foundation for guiding the design of titanium alloys that show improved tolerance to oxygen, and are thus less expensive to process and manufacture. Further, by leading to improved understanding of the mechanisms underlying slip and twinning processes in mechanical deformation, and the ways in which these mechanisms depend on material composition, the work will also provide an improved foundation for the development of predictive continuum deformation models that can be used to guide engineering-scale design.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 23, 2016
- Source ID
- N000141612304
Entities
People
- Mark Asta
Organizations
- Office of Naval Research
- United States Navy
- University of California Regents