Determination of Critical Microstructural Features in an Austenitic Stainless Steel Using Image-Based Finite Element Mod
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INTRODUCTION
IN recent years, the materials design process has become increasingly dependent on simulations and computational analyses to predict material behavior, with the result that new alloys are being developed in less time and for lower cost. In order to design alloys with improved mechanical properties, the interactions between microstructural features and applied loads must be understood. These microstructural features include grain size and morphology, crystallography, and grain boundary structure and connectivity. If the impact of specific microstructural features can be simulated and predicted, these features can be engineered to optimize the material microstructure and behavior to produce superior alloys. A number of researchers have used two-dimensional (2-D) and three-dimensional (3-D) microstructural representations as input for finite element (FE) simulations to determine the effects of microstructural morphologies on mechanical response. These include studies of simulated microstructures based on microstructural statisA.C. LEWIS, Materials Research Engineer, and A.B. GELTMACHER, Head, Imaging and Simulations Sections, are with the Multifunctional Materials Group, Naval Research Laboratory, Washington, DC 20375. Contact e-mail: [email protected] K.A. JORDAN, Research Assistant, formerly with the Multifunctional Materials Group, Naval Research Laboratory, is Student, Department of Mathematical Science, Clark Atlanta University, Atlanta, GA 30314. Manuscript submitted July 19, 2007. Article published online March 14, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
tics,[1–4] as well as image-based reconstructions, derived from real microstructures.[5–9] In the present work, 2-D and 3-D microstructural representations incorporating spatial and crystallographic information are used as direct input into image-based FE simulations.[10] These image-based FE modeling techniques incorporate measured crystallographic information in addition to morphological details. Visualization and analysis tools have also been developed to evaluate the mechanical behavior of the microstructures and to determine the correlations among various microstructural properties and material response. The incorporation of morphological and crystallographic data into a mesoscale mechanical model produces realistic simulations of the mechanical response of the material while employing fewer assumptions of the material microstructure. Qualitative measures, such as simultaneous visualization of the mechanical response and microstructural features, are used to determine which features are of interest for further investigation. Quantitative analysis of these features is then employed to determine which features might be beneficial or detrimental to material performance under a variety of service conditions.
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MATERIALS AND METHODS
The material examined in this study is AL-6XN, a commercial super-austenitic stainless steel. The asreceived material was in the form of a continuously cast and mill annealed (>1100 C) 6.35-mm-thick (¼
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