POWRE: A Fundamental Study of Microstructual Evolution in Titanium Alloy Friction Stir Welds

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

This project is aimed at greater understanding of fundamental mechanisms of high temperature deformation and microstructural evolution in titanium alloy friction stir welds. Two alloys have been selected, pure(CP) titanium and Ti-6Al-4V, a + b alloy. CP titanium, used for its corrosion resistance especially in the chemical process industry, was chosen for its good formability. Ti-6Al-4V is widely used in a variety of aerospace and marine applications in welded and unwelded conditions. In addition to "normal" welds, interrupted welds, where the tool is retracted before reaching the end of the two plates to be joined, will also be evaluated. In this way, the micro-structures of the thermomechanically-affected and heat-affected zones will be compared with material just ahead of the weld. These in turn will be compared with microstructures of the stir zone (the actual dynamically recrystallized weld) and the base material. Samples will be obtained for metallographic examination in both the transverse and longitudinal directions to reveal each distinct microstructural zone and serve as a map for the eventual location of TEM foils. A dual beam (electron beam + ion beam) Focused Ion Beam (FIB) will be used to remove TEM foils at precisely designated locations within the welds. This will greatly improve the chances of obtain-ing a foil with the desired microstructural information. Diffraction contrast techniques will be used on a Philips CM 200 and CM 300 Field Emission Gun TEMs to determine the details of the deformation processes, i.e., the development of deformation substructure (e.g., sub-grains and sub-bands), the occurrence of dynamic recovery and recrystallization, annealing effects, and phase transformations. Scanning electron microscopy will be performed on a Philips XL-30 FEG instrument using Orientation Imaging Microscopy to reveal possible microtexture that may be residual from the base material. The results of these microstructural studies will be used to complement process optimization and mechanical property data. %%% This is a research enhancement grant made under the Professional Opportunities for Women in Research and Education (POWRE) program. The PI plans to realign her career after a four-year hiatus in an administrative capacity. Prior to working as Aerospace Team Leader at Edison Welding Institute and Associate Director for the Center for the Accelerated Maturation of Mate-rials (CAMM) at the Ohio State University, she led an active technical career for 15 years. The research is expected to contribute basic materials science knowledge at a fundamental level of special relevance to the behavior of metals. The project is co-supported by the Division of Mate-rials Research, and the MPS OMA(Office of Multidisciplinary Activities). ***