Deformation and Transitions at Grain Boundaries: Anisotropy Effects on Grain Boundaries
Sponsored by: MS&T Organization
Program Organizers: Thomas Bieler, Michigan State University; Douglas Spearot, University of Arkansas; Rozaliya Barabash, Oak Ridge National Laboratory; Shen Dillon, University of Illinois at Urbana-Champaign; Jian Luo, Clemson University
Tuesday 2:00 PM
October 18, 2011
Room: C121
Location: Greater Columbus Convention Center
Session Chair: Hao Zhang, University of Alberta; David Rowenhorst, Naval Research Lab
2:00 PM Invited
Creep Damage Dependence on Grain Boundary Character in Ferritic-Martensitic Steels: David Field1; Zhe Leng1; 1Washington State University
Grain boundary damage occurs extensively in ferritic steels subjected to time dependent deformation in the regime of power law creep (or dislocation creep). Creep experiments were performed on tensile specimens made from HT9 steel. The test temperature was 600ºC with failure times on the order of 20 hours to 200 hours. Analysis of the microstructure before and after creep testing showed that significant evolution of the grain boundary character occurred during testing. Voids and cracks were observed almost exclusively along grain boundaries. Observations of grain boundary character showed that Sigma 3 boundaries according to Brandon’s criterion were extensively damaged. These boundaries were identified using the grain boundary character distribution with the five parameter description of grain boundary character. More extensive analysis suggests that slip system activity along these boundaries is likely of primary importance in analyzing these structures, thus requiring information relating the boundaries to the imposed stress state.
2:20 PM Invited
Influence of Grain Boundary Crystallography on the Nucleation Characteristics of Dynamic Failure: Mukul Kumar1; Roger Minich1; 1Lawrence Livermore National Laboratory
The scaling of mechanical properties with grain size is well known. However, the role of grain boundary crystallography is only recently starting to emerge in that the Hall-Petch scaling needs to be reformulated to take into account the frequency of crystallographically “special” boundaries in the microstructure. Less well developed is an understanding of the role of microstructures in void nucleation and growth during shock loading of materials. In this paper, we shall report on the scaling recently observed in the case of dynamic failure or spall under shock deformation conditions for different microstructures in high purity copper. The spall strength is observed to increase as the length scales coarsen, which is counter to the Hall-Petch relationship, eventually leveling off for single crystals. The role of nucleation site density and grain boundary character distribution in understanding this behavior as a function of impact pressure will be investigated using EBSD orientation mapping.
2:40 PM Invited
Crystallographic Anisotropies in Grain Boundary Interface Curvature: David Rowenhorst1; Alexis Lewis1; 1The US Naval Research Laboratory
Grain coarsening describes the process in polycrystalline systems wherein the grain boundaries move in a curvature driven process so that the interfacial energy of the system is reduced and the average grain size increases. In this presentation we will show that the curvature of the grain boundaries are partially determined by the crystallographic anisotropies present in grain boundary interfaces. Optical serial sections combined with EBSD scans are used to reconstruct the full 3D morphology and crystallography of approximately 4100 beta-Ti grains in Ti-21S. The grain boundary misorientation and inclination can be measured from the 3D reconstruction, thus providing all five macroscopic degrees of freedom of the grain boundary interface, as well as the local interfacial curvature. We will show that there are preferences for particular types of boundaries, and that the interfacial curvatures of these of these boundaries also demonstrate anisotropic behavior.
3:00 PM Break
3:20 PM
The Role of Grain Boundary Structure during Shock Loading: Ellen Cerreta1; Alex Perez-Bergquist1; Juan-Pablo Escobedo-Diaz1; Carl Trujillo1; George Gray1; Saryu Fensin1; Steven Valone1; Christian Brandl1; Timothy Germann1; 1Los Alamos National Laboratory
To understand the role of grain boundaries during dynamic deformation, four well-characterized copper grain boundaries have been studied under shock loading conditions. These boundaries can be separated into two categories: (1) 001/111 boundaries and (2) 001/001 boundaries. Their structures have been characterized prior to deformation using electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). This characterization has been utilized as input for molecular dynamic simulations to examine in-situ dislocation/grain boundary interactions at shocks of 2.5 and 10GPa. These simulations were mimicked experimentally in a gas gun. All specimens were soft recovered. Post-mortem characterization revealed that high angle grain boundaries readily form damage during shock loading but special boundaries (such as Σ3 boundaries) are resistant to failure. This is linked to differences in slip transmissibility and grain boundary motion during shock deformation.
3:40 PM
Development of Grain Boundaries during Solidification of Anisotropic Materials: Om Singh1; 1K. N. Post Graduate College
This paper focuses on the development of grain boundaries during controlled solidification of pure and binary anisotropic materials. A detailed comparison will be made with isotropic materials t understand the effect of solid-liquid ainterface anisotropy. The results will be presented for the transparent organic materials since quenched morphology does not represent the real time results.We observed tilted boundaries and strong interface twisting in anisotropic material compared to material which was anisotropic.
4:00 PM Invited
Grain Boundary Sliding in FCC and HCP Metals: Hao Zhang1; 1University of Alberta
We performed a series of molecular dynamics simulations of bicrystal in which we apply a fixed shear rate parallel to the boundary plane in fcc nickel and hcp magnesium. Under some conditions, grain boundary motion is coupled to the relative tangential motion of the two grains. In nickel, the data points to the existence of two critical stresses: one for coupled shear/boundary motion and the other for grain boundary sliding. Especially, for the non-Σ boundaries, the critical stress for coupled shear/boundary motion is typically smaller than that for sliding -- coupled shear/boundary motion occurs for all inclinations. In magnesium, simulations showed that grain boundary sliding did not occur over the stress range applied; instead, coupled shear/boundary motion was dominant. While the measured coupling coefficient was in good agreement with theoretical prediction, the detailed shear behavior was different, depending on types of grain boundary, magnitude of applied shear stress and temperature.