Grain Boundary Lifetimes
Shen Dillon and Gregory Rohrer
Supported by the MRSEC Program of the NSF under award number DMR-0520425

The types of grain boundaries that make up the interfacial network within polycrystalline solids influence the properties and performance of the material. The population of grain boundary types is anisotropic, meaning that some of the types are found more frequently than others. The origin of these anisotropic populations was unknown until our recent discovery showed that the energy of a boundary is a key factor in determining which boundaries are shrinking and which are growing: low energy boundaries are growing and therefore have longer lifetimes while high energy boundaries are shrinking and have shorter lifetimes. This leads to anisotropic grain boundary populations that are dominated by low energy boundaries. This discovery, made using experimental techniques developed by the CMU MRSEC, has led to a model for the evolution of grain boundary character distributions that will potentially allow the processing of improved materials.

Figure 15.1. (a) By inspecting the curvature of adjoining grain boundaries in Atomic Force Microscope images, boundaries could be categorized as lengthening, shortening, or random. (b) The energies of the grain boundaries have distinct distributions. This research is described more completely in the publication: Dillon and Rohrer, Acta Materialia 57 (2009) 1-7.

Past Nuggets

• PREM collaboration yields scientific and educational results (Research Partnership Nugget: 03/09)
• Grain Boundaries in Block Copolymers (SEED Nugget: 03/09)
• Seeing Inside Solids (Research Nugget: 03/08)
• The Origin of Resistivity in Nanoscale Conductors (Research Partnership Nugget: 03/08)
• Automated Grain Boundary Analysis of Transmission Electron Micrographs (Research Partnership Nugget: 03/08)
• Talk to the Professors (Education Nugget: 03/08)
• X-ray Vision for Materials
  
• International Collaboration on Grain Boundary Engineered Materials (Research Partnership Nugget: 06/06)
• High School Teacher Gains Recognition For Work with the CMU MRSEC (Education Nugget: 06/06)
• Growing Thin Films with Only One Hand (Research Nugget, 3/05)
• Large Scale, Anisotropic Grain Growth Simulations (Research Partnership Nugget: 03/05)
• Predictability and Control in Polycrystalline Structure (Research Nugget: 11/04)
• Polycrystals Have Good Habits (Research Nugget: 6/04)
• Do You Really Need Titanium Golf Clubs? (Education Nugget: 8/04)
• What should the three little pigs really have used? (Education Nugget: 8/04)
• Synchronized Transatlantic Synchrotron Research (International collaboration nugget: 11/03)
• Powering Future Engines (Education Nugget: 8/03)
• 5-D Vision (Research Nugget: 1/03)
• Measurement of Relative Grain Boundary energies (Research Nugget: 3/02)
• Discovery of Texture in the Space of Grain Boundary Planes (Research Nugget: 1/01)
• Experimental Determination of Relative Grain Boundary Mobilities in Al Alloys (Research Nugget: 1/00)

Movies illustrating Results

• Watch a movie illustrating illustrating five-dimensional grain boundary character distribution results. As the movie runs, the 2D plots illustrate the distribution of grain boundary planes at different points in the 3D misorientation space. The current point in the 3D space is illustrated in the lower right and the current bicrystal configuration is illustrated in the lower left. In the upper portion, data recorded by traditional means (left) and recovered from the new statistical procedure (right) are compared. All illustrations are for [100] type misorientations in SrTiO₃.
• Habit data for WC crystals. As the movie progresses, more and more observations from planar sections are added to the distribution, until the peaks at the basal and prismatic positions become relatively constant.
• Watch a movie illustrating the distribution of planes for MgO grain boundaries with misorientations about <110>. In this movie, the distribution of planes is plotted as the angle of misorientation about <110> increases from 5 to 60 degrees during the progress of the clip.
• Two dimensional grain growth simulation by David Kinderlehrer
• Watch a simulation of grain growth