Interface-Mediated Properties of Nanostructured Materials: Measurement and Modeling of Nanoscale Deformation
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Caizhi Zhou, Missouri University of Science and Technology; Nan Li, Los Alamos National Laboratory; Peter Anderson, The Ohio State University; Michael Demkowicz, Texas A&M University

Tuesday 2:00 PM
February 28, 2017
Room: Pacific 23
Location: Marriott Marquis Hotel

Session Chair: Peter Anderson, The Ohio State University; Michal Demkowicz, Texas A&M University

2:00 PM  Invited
Slip Transmission in fcc/fcc Bilayers Using Phase Field Dislocation Dynamics: Yifei Zeng1; Abigail Hunter2; Irene Beyerlein2; Marisol Koslowski1; 1Purdue University; 2Los Alamos National Laboratory
    We use a phase field dislocation dynamics model to study the effect of lattice and moduli mismatch on the critical stress required to transmit dislocations across a bimaterial interface with a cube-on-cube orientation relationship. Our calculations predict that the critical stress for transmission from material 1 to 2 is not the same as from material 2 to 1. It is found that transmission from the material with the lower shear modulus is easier than the reverse and this degree of asymmetry is directly proportional to lattice mismatch. An analytical model based on the formation energy of the residual dislocation is presented and from it emerges a scaling factor for the critical stress with lattice and moduli mismatch. Often dislocations are required to transmit across interfaces that have already been crossed by prior ones. Last, we show calculations on the effect of primary transmissions on subsequent transmissions.

2:30 PM  Invited
Strengthening Mechanisms of Nanoporous Metallic Materials : Niaz Abdolrahim1; Bin Ding1; 1University of Rochester
     Nanoporous (NP) metallic materials exhibit microscale plasticity, but macroscopically fail in a relatively brittle manner. The deformation behaviors of NP materials are often controlled by their microstructure. Here we study the governing deformation mechanisms responsible for ductile behavior of the constituent ligaments of NP structure (nanowires) and discuss the origin of the the brittle behavior of the NP structure. We explore the role of structural and morphological parameters including surface and interface effects, ligament and pore sizes, orientation and loading direction, and density of pores and ligaments on the overall deformation behavior of the NP structure and provide guide maps for designing NP materials with enhanced ductility. Our preliminary results suggest that core-shell ligaments can increase both ductility and strength of the NP structure due to the increased activity of twins while nucleation of partials are prominent in monolithic ligaments with no shells.

3:00 PM  
Deformation and Fracture in Stressed Multi-layer Thin Films: Ruth Konetschnik1; Darjan Kozic2; Ronald Schöngrundner2; Hans-Peter Gänser2; Roland Brunner2; Daniel Kiener1; 1University of Leoben; 2Materials Center Leoben
     Miniaturization of devices has led to increasingly complex thin film combinations, requiring miniaturized tests to study the local material response. Here, we address the influence of local residual stresses on the fracture behaviour of thin films. The materials investigated are Cu-W-Cu and W-Cu-W trilayer systems with individual layer thicknesses of 500 nm. Samples are fabricated via cross-section polishing and focused ion beam milling, and residual stress depth profiles are determined by an improved ion beam layer removal method, where stresses are calculated from deflections of a cantilever. Subsequently, fracture experiments parallel and perpendicular to the interfaces are performed in-situ in the SEM to obtain the fracture and interface toughness. An accompanying finite-element approach is introduced to determine crack-driving forces in the presence of interfaces and residual stresses.We emphasize the importance of elastic and plastic incompatibilities and residual stresses when addressing fracture mechanical quantities of multi-layered thin film systems.

3:20 PM  
Green’s Function Formulation for Vacancy-assisted Dislocation Climb and Applications to Low Angle Grain Boundaries: Yang Xiang1; Yejun Gu1; Jian Han2; David J Srolovitz2; 1Hong Kong University of Science and Technology; 2University of Pennsylvania
    We propose a Green's function formulation for the vacancy-assisted climb of curved dislocations and multiple dislocations in three-dimensions. In this new dislocation climb formulation, the dislocation climb velocity is determined from the Peach–Koehler force on dislocations through vacancy diffusion in a non-local manner. The long-range contribution to the dislocation climb velocity is associated with vacancy diffusion rather than from the climb component of the well-known, long-range elastic effects captured in the Peach–Koehler force. We employ this formulation to study the relaxation of low-angle grain boundary structure by climb of the constituent dislocations. With inclusion of this new long-range effect, we show that dislocation climb has a fundamentally different effect on the stability of low-angle grain boundaries than dislocation glide. We also apply this formulation to study the low angle tilt grain boundary point defect sink efficiency.

3:40 PM Break

3:55 PM  Invited
Ab Initio Determination of the Energetics of Atomically Sharp Interfaces: Liang Qi1; 1University of Michigan
    The energetics of atomically sharp interfaces, such as stacking faults, twin boundaries, and interphase boundaries, are critical for many physical, chemical and mechanical properties of materials. However, it is difficult to calculate these interfacial energies based on ab-initio calculations, except for some special cases such as the coherent interfaces between two ordered crystal crystals. Here I demonstrate three recent attempts to calculate the energetics of interfaces beyond these special cases. First, the energetics of the sharp interfaces inside the binary solid solution alloys are calculated based on special-quasi-random (SQS) methods and first-principles calculations. Second, the energetics of the sharp interfaces inside the binary alloys with certain degrees of short-range ordering is investigated base on artificial neural network atomistic potentials and first-principles calculations database. Third, the shape interfaces between certain amorphous materials and metals are calculated with the help of classical molecular dynamics (MD) simulations and ab initio MD simulations.

4:25 PM  
Molecular Dynamics Simulations of Mg/Nb Interfaces: Shear Strength and Interaction with Lattice Glide Dislocations: Xiang-Yang Liu1; Satyesh Yadav1; Shuai Shao1; Jian Wang2; Youxing Chen1; Richard Hoagland1; 1Los Alamos National Laboratory; 2University of Nebraska-Lincoln
    In this work, molecular dynamics (MD) simulations are carried out to understand the mechanical response of Mg/Nb interfaces, as a prototype hcp/bcc interfaces, employing a recently developed Mg-Nb EAM potential. First, the shear responses of the interfaces are studied under mechanical loading. The interfacial shear mechanisms are analyzed. Second, the interactions of lattice glide dislocations with the interfaces are studied, with the simulations focusing on the extent of interface shear and the dislocation core spreadings at the interfaces as lattice glide dislocations approaching the interfaces. These results are then correlated to the interface misfit dislocation patterns at the interfaces, highlighting the importance of interface misfit dislocations in determining the detailed mechanical response of the interfaces.

4:45 PM  
On the Impact of Capillarity for Strength at the Nanoscale: Nadiia Mameka1; Jürgen Markmann1; Jörg Weissmüller2; 1Helmholtz-Zentrum Geesthacht; 2Hamburg University of Technology
     Nanoporous metals made by dealloying offer a convenient model material system for investigating crystal plasticity at the nanoscale. The possibility of adjusting a structural size over a wide range, from a few nanometers to several microns, large specific surface area, precise control of the surface state by electrochemical means, and applicability of macroscopic testing schemes enable probing surface phenomena observed in nanoobjects in bulk nanostructural materials. Here we explore the impact of interface properties – surface tension and surface stress – on the flow stress behavior of a nanomaterial. This is implemented in situ by deforming nanoporous gold wetted by electrolyte while distinctly different variations on the two capillary parameters are imposed under control of an applied electric potential. The experimental findings, together with our analysis of the mechanics, reveal a significant contribution of the surface tension on strength at the nanoscale and reject the impact of the surface stress.

5:05 PM  
Mitigation of Atomic Oxygen Attack to Spacecraft Composite Structures: A Fundamental Investigation Using Reactive Molecular Dynamics Simulation: Sasan Nouranian1; Farzin Rahmani1; Mina Mahdavi1; Ahmed Al-Ostaz2; 1Department of Chemical Engineering, University of Mississippi; 2Department of Civil Engineering, University of Mississippi
    In this work, we performed a series of molecular dynamics simulations using the Reactive Force Field (ReaxFF) to investigate the degradation extent of a pure aerospace-grade polyimide (PI) resin and PI enhanced with polyhedral oligomeric silsequioxane (POSS), silicon dioxide (SiO2), graphene (Gr), and graphene oxide (GO) nanoparticles in different concentrations. Hypervelocity atomic oxygen attack is a prevalent phenomenon in Low Earth Orbit (LEO), which extends from the Earth’s surface at sea level to an altitude of about 2,000 km. Many satellites are stationed in this orbit and an impact by energetic atomic oxygen species at high velocities causes damage to these satellites, leading to catastrophic failure of their outer structural material layer. In this study, the physics and chemistry of material failure in this extreme environment is revealed. Moreover, we quantify the extent of damage mitigation by the presence of nanoparticles and compare our results to the experimental data.

5:25 PM  
Joining of Copper by Ag Nanopaste: Microstructure and Strength Behavior Depending on Different Process Parameters: Susann Hausner1; Bernhard Wielage1; Guntram Wagner1; 1Technische Universitaet Chemnitz
    Nanoparticles exhibit a decreased sintering and melting temperature with decreasing particle size in comparison to the corresponding bulk material. After melting or sintering of the nanoparticles, the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of big interest for various joining tasks. Joints (substrate: Cu) were prepared with an Ag nanopaste. The influence of different process parameters on the microstructure and the strength behavior of the joints was investigated. It is shown that in particular the joining pressure exerts an essential influence on the microstructure and the achievable strengths. In addition, joining temperature, holding time and thickness of paste application have a significant effect. Other varied process parameters like heating rate, pre-drying process, surface pre-treatment and subsequent heat treatment possess hardly any influence on microstructure and joint strength.