Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Crystal Defects: Experiments and Modeling/Simulation
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Indrajit Charit, University of Idaho; Yuntian Zhu, North Carolina State University; Stuart Maloy, Los Alamos National Laboratory; Peter Liaw, University of Tennessee - Knoxville

Tuesday 8:30 AM
February 28, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Anter El-Azab, Purdue University; Ram Devanathan, Pacific Northwest National Laboratory

8:30 AM  Keynote
Helium Hardening in Interface-dominated Metallic Composites: Amit Misra1; Nan Li2; 1University of Michigan; 2LANL
    This presentation will overview an approach to engineer interphase boundaries in metallic composites to achieve superior resistance to void swelling and helium bubble hardening. Model composite systems of face-centered-cubic (Cu) and body-centered-cubic (Nb, Mo or V) metals are used to elucidate the effects of boundary structure and spacing on the damage accumulation and mechanical properties after helium ion implantation. Transmission electron microscopy (TEM) and nano-mechanical testing are used to characterize the irradiation response. The hardening is correlated with the density of helium bubbles that scales with the density of misfit dislocation intersections at the interface.

9:00 AM  Invited
On Dislocation Patterning in Deformed Crystals: Anter El-Azab1; 1Purdue University
    We present a continuum dislocation dynamics model for mesoscale plasticity that predicts the formation of dislocation cell structure in fcc crystals under tensile loading, in conjunction with the similitude law for the dependence of cell size on stress. This model features dislocation transport equations coupled with crystal mechanics, plus a closure problem consisting of finding the spatial and temporal correlations of the dislocation system. This approach has been used to obtain a full solution of the deformation problem, including the dislocation and deformation patterns, internal elastic fields, and stress-strain response. The results reveal the critical role of cross slip in cell structure formation under monotonic loading, and the relative suppression of this role when cyclic loading is applied. The dependence of dislocation patterns on loading axis will be presented and discussed. This work was performed in collaboration with Shengxu Xia (Purdue University).

9:20 AM  Invited
Role of Structural Defects on the Magnetostriction of α-phase of Fe-based Alloys: Sivaraman Guruswamy1; Kanagasundar Appusamy1; Travis Willhard1; Richard Laroche1; 1University of Utah
    Fe-based terminal solid solution alloys have been shown to be attractive for use in magnetostrictive senosrs and actuators. Various metallurgical factors influence the magnetostrictive response in these alloys. Of particular interest are dislocations and point defects. This paper will present an overview of the examinations of structural ordering and dislocation structures in Fe-based alloys and how they influence magnetostriction.

9:40 AM  Cancelled
Non-basal Dislocations in HCP Mg: Yizhe Tang1; 1Shanghai University
    The ease of basal slip in HCP Mg makes plastic deformation quite active on the basal planes. On the other hand, non-basal dislocations, which are also requisites for accommodation of plastic deformation, turn out to be very inactive and are believed to be responsible for the brittleness of HCP metals. The present study employs molecular dynamics simulations with the MEAM potential of Mg to systematically investigate the slip behavior of all non-basal dislocations, including <c+a> dislocations on pyramidal I, pyramidal II, prism and {11-21} planes, <c> dislocations on prism planes and <a> dislocations on prism and pyramidal I planes. The initial dislocation configurations were introduced by specifying the required elastic displacement fields. The core structures, dissociation and Peierls stresses will be presented, and the relatively complete results will be discussed in comparison with experiments observations, in order to get a comprehensive understanding of non-basal slip in HCP metals.

10:00 AM Break

10:15 AM  Keynote
Precipitate-dislocation Interaction Mediated Portevin-Le Chatelier-like Effect in a Beta-stabilized Ti-Mo-Nb-Al Alloy: Deep Choudhuri1; Srinivas Mantri1; Talukder Alam1; Rajarshi Banerjee1; Srikumar Banerjee2; 1University of North Texas; 2Bhabha Atomic Research Centre
    Portevin-Le Chatelier (PLC)-like effect was observed in a commercial alloy based on Ti-Mo-Nb-Al, which exhibited serrations in its tensile stress-strain response within a temperature-strain rate window. The serrations manifested as repeated load-drop and rise, and were rationalized on the basis of sudden plastic flow along the “soft” ω precipitate free micro-slip-bands created by the passage of leading dislocations in the parent β matrix. Subsequently, dynamic precipitation of the α phase occurred within the ω-free micro-slip-bands. These results demonstrate that the PLC-like effect can be manifested via precipitate-dislocation interactions, and is not limited to the traditionally accepted solute-dislocation interactions.

10:45 AM  Invited
Molecular Dynamics Simulations of Dislocation – Obstacle Interactions: Brian Wirth1; 1University of Tennessee
    Irradiation effects impact structural materials performance in nuclear environments, as defect production, diffusion and ultimately cluster formation can impede the motion of dislocations producing radiation hardening. This presentation will review the results of atomistic molecular dynamics simulations, as compared to observations from in-situ transmission electron microscopy of dislocation motion in irradiated materials, to assess the key mechanisms by which dislocations interact with and bypass obstacles. The results from such studies have guided the development of advanced constitutive models for the stress-strain response of irradiated structural materials, and are also known to influence the creep and creep-fatigue behavior. In particular, we highlight the role of dislocation character (screw or edge) in both FCC and BCC materials, as well as the type of defect obstacle, including precipitates, cavities or stacking fault tetrahedron.

11:05 AM  Invited
Atomistic Simulation of Radiation Effects in FeCr-based Cladding: Ram Devanathan1; 1Pacific Northwest National Laboratory
    We present the findings of classical molecular dynamics simulations of thermal expansion and defect production by energetic displacement cascades in FeCr alloys for seven different compositions. The simulations used a two-band model based on the embedded atom method. The coefficient of linear thermal expansion in the temperature range from 300 K to 1050 K was essentially unchanged with Cr content and was about 1.2x10-5/K. The specific heat at constant pressure (Cp) at 600 K was about 0.5 J/g/K and almost independent of Cr content. These values are in reasonable agreement with experimental findings in the literature. We also simulated recoils of 1-30 keV energy for seven different compositions. Cr atoms were preferentially displaced. We will discuss the details of defect production, the role of defects in enhanced Cr precipitation under irradiation at elevated temperature, and implications for the degradation of thermomechanical properties of FeCr alloy-based fuel cladding.

11:25 AM  Invited
On the Origin of the Sink Efficiency of Grain Boundaries under Irradiation: Blas Uberuaga1; Enrique Martinez1; Laurent Capolungo1; 1Los Alamos National Laboratory
    In the ongoing effort to develop improved radiation-tolerant materials, one promising strategy is to introduce a high density of interfaces that enhance the annihilation of radiation-induced defects. However, the relationship between the atomic structure of a given interface and the ability of that interface to enhance annihilation mechanisms is still unclear. Here, using grain boundaries in Cu as a model system and a combination of simulation methodologies from accelerated molecular dynamics to kinetic Monte Carlo and cluster dynamics, we find that one key property that impacts defect annihilation and thus sink efficiency is the mobility of defects within grain boundary planes. This mobility, in turn, depends on the atomic structure of the grain boundary. The sink efficiency is dictated by in-boundary annihilation rates which are a direct function of the defect mobilities within the boundaries. We discuss the ramifications of these results on the radiation tolerance of nanomaterials more generally.

11:45 AM  Invited
Application of Phase-field Approach in Deformation-induced Microstructure Evolution: Yulan Li1; Shenyang Hu1; Scott Whalen1; Suveen Mathaudhu1; 1Pacific Northwest National Laboratory
    Phase field approach has been successfully used to predict the microstructure evolution in many important materials processes such as solidification, precipitation, and multiferroic domain evolution. The deformation due to lattice mismatches and applied stresses can be one of main driving forces for microstructure evolution. In order to capture the impact of non-uniform deformation of polycrystalline on microstructure feature, crystal plasticity formulations were developed for considering crystal orientation and dislocation slip systems of each grain. We will present an efficient method to find the elastic-plastic solution in polycrystalline and a phase field model to integrate crystal plasticity and microstructure evolution. The developed model has been used to study 1) effect of the microstructures in bimodal and dual phase polycrystallines on elastic-plastic deformation and 2) effect of plastic deformation on dynamic recrystallization. Its potential application in optimizing material fabrication processes and predicting creep deformation and fracture will be discussed.