EBSD investigations of crystallographic orientation scatter in the martensitic transformation

• Applicants: Dr. Gert Nolze, since 6/2013; Professorin Dr. Victoria Yardley
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2012 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 225513160

In the martensitic transformation, changes in crystalline structure of metallic alloys occur through the diffusionless cooperative motion of atoms. This is exploited in many materials to produce shape memory effects or excellent mechanical properties through a fine microstructure consisting of numerous crystallographic variants. In iron-based alloys, a large degree of scatter is observed experimentally in both the orientation relationship (OR) and the habit planes of these variants, and the OR is frequently observed to deviate by a few degrees from two idealized orientation relationships, Nishiyama-Wassermann and Kurdjumov-Sachs. Measurement of the exact ORs by conventional transmission electron microscopy methods is an extremely tedious task that normally requires the existence of some residual austenite phase and can only be used to examine relatively small regions within a single specimen. High-speed automated electron backscatter diffraction (EBSD) has emerged in recent years as a powerful technique for simultaneously characterizing the spatial and crystallographic relationships in microstructures. In this project, the experimentally-observed ORs will be characterized directly from EBSD data, allowing for the collection of statistically significant data (~1E4 more boundary observations than possible by conventional TEM) on the factors that affect the scatter in addition to elucidating the reasons for the observed scatter. This data will be compared to models of martensitic transformations, allowing the theoretical underpinnings of the models to be more fully assessed. The results are expected to lead to improved algorithms for EBSD-based reconstruction of the prior parent austenitic microstructures from observations of martensite, which is a prerequisite to improving our understanding of how the austenite microstructure affects the transformation products.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Eric J. Payton, Ph.D., until 6/2013