Magnesium Technology 2021: Fundamentals of Plastic Deformation
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: Victoria Miller, University of Florida; Petra Maier, University of Applied Sciences Stralsund; J. Brian Jordon, Baylor University; Neale Neelameggham, IND LLC
Tuesday 2:00 PM
March 16, 2021
Room: RM 31
Location: TMS2021 Virtual
Session Chair: Tracy Berman, University of Michigan; Sean Agnew, University of Virginia
2:00 PM Invited
Accounting for the Effects of Dislocation Climb Mediated Flow in Mg alloy ZK10 Sheet: Michael Ritzo1; Sean Agnew1; 1University of Virginia
A version of the viscoplastic self-consistent (VPSC) code, which accounts for the kinematics of dislocation climb, is used to model conditions where hard slip modes and twinning are also observed. Tensile samples of a Mg alloy ZK10 sheet were tested at a range of temperatures and strain rates designed to rather evenly probe a range of Zener Hollomon parameter values, from ln(Z) ≈ 15 (10-4 s-1 and 623K) up to ln(Z) ≈ 50 (10-3 s-1 and 300K). ZK10 shows modest strain anisotropy (r-value) for both 45° (r ≈ 0.84-1.2) and TD (r ≈ 0.89-1.4) sample orientations, despite the propensity for prismatic slip of <a> dislocations, which often leads to high r-values in basal textured sheets. This is explained in terms of the initial texture and mechanism activity, including twinning at both room and elevated temperature, where basal glide and climb of <a> dislocations become the dominant deformation mechanisms.
2:30 PM
Three Dimensional Interaction of {101 ̅2} Twins with Tilt Boundaries in Mg: Twin and Dislocation Transmission: Khanh Dang1; John Graham1; Carlos Tome1; Vincent Taupin2; Laurent Capolungo1; 1Los Alamos National Laboratory; 2LEM3
While both dislocations and deformation twins accommodate plastic shear in Mg, the former are line defects while the latter are three-dimensional domains bounded by numerous complex interfaces. As such, both kinetics and kinematics of twin transmission is more complex than that of dislocations. In this work, using atomistic simulations and phase field modeling, we study the reactions associated with the interactions between twins and tilt boundaries. We find that the byproduct of short-range interfacial interactions can either be a new twin or a dislocation, depending on the geometrical alignment of the slip and/or twinning systems, resolved shear stress, and interactions between intrinsic defects within the twins and grain boundaries. Originally, we find that lateral twin transmission is easier than forward twin transmission. Using phase field we systematically investigate the role played by facet energies and mobilities as well as internal stresses on lateral and forward transmission into neighboring grains.
2:50 PM Invited
Revisiting <c+a> Pyramidal Slip in Magnesium: Jaafar El-Awady1; 1Johns Hopkins University
In this talk we will revisit the characteristics of <c+a> pyramidal slip in magnesium. In particular, literature over the past few years has been dominated by conflicting atomistic simulation results that in many cases directly conflict with experimental observations in terms of the lack of ductility at room temperature versus the transition to large ductility at elevated temperatures. To overcome these conflicting results in literature, here we revisit the predictions from atomistic simulations in view or recent experimental studies to develop a more proper understanding of <c+a> pyramidal slip in magnesium. In particular, the traditional view of plasticity being dominated by a single pure screw or pure edge dislocation does not hold for pyramidal slip. Instead a holistic view of the collective behavior of dislocations and the characteristics of mixed dislocation must be accounted for.
3:20 PM
Thermally Activated Nature of Basal and Prismatic Slip in Mg and Its Alloys: Mohammed Shabana1; Jishnu Bhattacharyya1; Marek Niewczas2; Sean Agnew1; 1University of Virginia; 2McMaster University
Some Mg alloys have been observed to exhibit dynamic strain aging, serrated flow, or the Portevin-Le Chatelier (PLC) effect. Curiously, the effects occur at RT in some alloys and at higher temperatures in others. The observations are distinct from more common FCC and BCC alloys, which exhibit these phenomena in a given temperature and strain rate range, which is explainable in terms of dislocation velocities, obstacle spacings, and solute diffusivities. The lecture will begin with a survey of the observations and recent theoretical advances. Explanations for the diverse observations in Mg alloys will be suggested in terms of the diverse deformation mechanisms (basal and non-basal slip and twinning) known to operate in these alloys as well as the diverse microstructures (textures, grain sizes, and precipitates) present in the materials.
3:40 PM
Mechanisms and Machine Learning for Magnesium Alloys Design: Zongrui Pei1; 1National Energy Technology Laboratory
We will show our extensive high-throughput studies for Mg alloys through both the dislocation and twinning mechanisms. Possible descriptors for the mechanisms are explored and a united picture is demonstrated, which is consistent with available experiments. There are two major contributions of this work, i.e., (i) The relationship between two well-acknowledged deformation mechanisms based on dislocations is clarified; (ii) Machine learning models show that it is possible to design ductile Mg alloys without the prior knowledge for deformation mechanisms.
4:00 PM
Three Dimensional Atomistic Simulations of {101 ̅2} Non-cozone Twin -- Twin Interaction in Mg – Role of Twin Stability and Mobility: Khanh Dang1; Carlos Tomé1; Laurent Capolungo1; 1Los Alamos National Laboratory
Given the ease of activation of tensile twinning on the {101 ̅2} planes in Mg, multiple {101 ̅2} twin variants can be activated and interact with each other. The outcomes of these interactions are twin-twin junctions (TTJs) that can serve as initiation sites for microcracks. Here, we investigate the 3-D structural characteristic and evolution of the non-cozone {101 ̅2} twin-twin junctions using atomistic simulations. This comprehensive approach allows us to identify additional twin-twin boundaries (TTBs) such as the TTBBP and TTBK2. They forme due to the interaction between the basal prismatic (BP) and conjugate twin (K2) interfaces with the coherent twin boundary (CTB). Moreover, the TTJs associated with the {1 ̅21 ̅2} TTBs are found to promote the growth of the 3-D twin along the normal and forward direction of the twin during the interaction, and hinder the detwinning process when loading is reversed.