Mechanical Behavior of Nanostructured Materials: Modeling and Thermal Stability, Radiation, Corrosion of Nanocrystals
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Xinghang Zhang, Purdue University; Yuntian Zhu, North Carolina State University; Joseph Poon, University of Virginia; Suryanarayana Challapalli, University of Central Florida; Enrique Lavernia, University of California, Irvine; Haiyan Wang, Texas A&M University

Wednesday 2:00 PM
March 1, 2017
Room: 30D
Location: San Diego Convention Ctr

Funding support provided by: AJA International; Hysitron Inc.

Session Chair: Xinghang Zhang, Purdue University; John Balk, University of Kentucky; Aashish Rohatgi , Pacific Northwest National Laboratory

2:00 PM  Invited
Computational Studies of Materials Properties at the Nanometer Scale: Donald Brenner1; 1North Carolina State University
    We have been using first principles methods, molecular simulation, meso-scale approaches and hybrid atomic-continuum techniques to characterize the nanometer-scale structure, stability and mechanical properties of a number of nanostructured systems. These systems include nanostructured metals stabilized by solute segregation to grain boundaries, nano-scale precipitates in advanced aluminum-copper alloys, asperity contacts under electro-magnetic loading, nanostructured thermites, and high entropy oxides and borides. This talk will include a brief overview of the computational challenges associated with these systems, followed by recent results on the properties of interfaces between ordered and disordered sublattices in high entropy oxides, nitride and borides. These advanced materials are being explored for ultra-high temperature applications, which require not only high melting temperatures, but also mechanical and phase stability as well high thermal conductivity and resistance to thermal shock. This work is supported by the Office of Naval Research through a Multi-Disciplinary University Research Initiative.

2:25 PM  Invited
Toward Quantitative 3D Microstructure-property Relations in Nano- and Poly-crystalline Materials: Mo Li1; 1Georgia Institute of Technology
     Structure-property relation is hailed as one of the three pillars of materials science. However, such relation has remained largely empirical or qualitative, especially for polycrystalline materials. As compared with single crystals, microstructure of polycrystalline materials has far more microstructural variables. How to quantitatively describe them and then apply the microstructure information in establishing connection with material properties remains a grand challenge in materials science.Microstructure in polycrystalline materials, either coarse-grained or nano-crystalline, is characterized by complex topological structure of grain boundary networks which are composed of an array of geometric entities with different dimensions. Collectively, they contribute to the materials’ properties. In this talk, I present recent developed algorithms and numerical methods in polycrystalline samples and how we can exploit the structure-property relations. Such quantitative methods enable detailed and rigorous treatment of microstructures in a wide range of modeling applications, including both atomistic simulation and continuum modeling.

2:50 PM  
Understanding, Controlling, and Creating Martensitic Phase Transformations in Nanostructured Polycrystals and Metamaterials: Sam Reeve1; Yang Wang1; Karthik Guda Vishnu1; Alejandro Strachan1; 1Purdue University
    We recently demonstrated tuning of properties with martensitic phase transformations of shape memory materials via epitaxial integration of dissimilar materials to engineer the energy landscape that governs the phase transition. Here we extend this work with the objective of engineering novel properties in metallic alloys via energy landscape engineering. We used large-scale molecular dynamics (MD) to study core/shell nanowires consisting of NiAl (non-transforming B2 phase) and Ni63Al37 phase transformation materials. This choice is motivated by an analysis of the energy vs. lattice parameter of the combined metamaterial that indicates epitaxial integration would result in ultra-low stiffness metallic systems. Explicit MD simulations of mechanical deformation of the core/shell nanowires reveal a variety of interesting properties including ultra-low stiffness (~4 GPa) while maintaining strength. The simulations reveal nucleation and propagation of martensitic transformation in the metamaterials and show spatial coexistence of austenite and martensite phases can be stabilized, resulting in ultra-low stiffness.

3:10 PM  
Electromechanical Coupling Enhanced by Polar Nanoregion Vibrations: Michael Manley1; Douglas Abernathy1; Raffi Sahul2; Jeff Lynn3; Andy Christianson1; Paul Stonaha1; John Budai1; 1Oak Ridge National Laboratory; 2Meggitt Sensing Systems; 3National Institute of Standards and Technology
    Relaxor-based ferroelectrics exhibit a giant electromechanical coupling that has revolutionized sensor and ultrasound applications. A long-standing challenge has been to understand how these responses occur when the underlying polar atomic displacements are partially broken into polar nanoregions (PNRs) in relaxor-based ferroelectrics. Using neutron scattering measurements of lattice dynamics and local structure, we find that PNR vibrations enable the giant coupling by softening macro-domain polarization rotations in relaxor-based ferroelectric PMN-xPT ((1 − x)[Pb (Mg1/3 Nb2/3)O3 ]–xPbTiO3) (x = 30%). The mechanism involves the collective motion of the PNRs with transverse acoustic phonons and results in two hybrid modes, one softer and one stiffer than the bare acoustic phonon. The softer mode is the origin of the macroscopic shear softening. Furthermore, the PNRs align in an electric field and this enhances the shear softening further, revealing a way to tune the ultrahigh piezoelectric response by engineering the elastic shear softening.

3:30 PM Break

3:50 PM  Invited
Development of Age-hardenable Nanolamiate Thin Films: David Bahr1; Chang-Eun Kim1; Nicolas Briot2; T. Balk2; 1Purdue University; 2University of Kentucky
    Strengthening mechanisms, such as those do to grain size refinement or precipitation hardening, are generally considered to be additive. In nanometallic multilayers (NMM) have the additional strengthening mechanism of confined layer slip. To examine the total strengthening from test these relationships, a NMM was fabricated using a 30 nm layer thickness as a bi-layer of Cr and Cu with 2%Cr multilayer by magnetron sputtering. By annealing the samples Cr is precipitated in the Cu layer, and decreases solid solution content while increasing the precipitate content. Hardness changes as a function of annealing condition were measured with nanoindentation; moderate temperature anneals of 30 minutes at 383K in an inert environment lead to an increase in hardness from 7 to 8.5 GPa, and retain strength up to anneals above 600K. These multiple mechanisms have been evaluated using molecular dynamics to establish strength relationships in age-hardenable NMMs.

4:15 PM  Invited
Mechanical Properties and Thermal Stabilization of Nanocrystalline Aluminum and Aluminum Alloys: Khaled Youssef1; Ronald Scattergood2; Carl Koch2; 1Qatar University; 2North Carolina State University
    The development of bulk nanomaterials for structural applications has been severely limited by the poor tensile ductility and the thermally unstable nanograins at low temperatures. The poor ductility is attributed to defects introduced by processing, and/or the low strain-hardening capacity of nanograins. ln few cases where defects are eliminated, exceptional combinations of high strength and good ductility have been demonstrated. The poor thermal stability of nanocrystalline metals is a result of the large excess energy/volume of the grain boundaries. A limited number of studies have demonstrated that thermal stability of nanocrystalline alloys can be improved. This has been attributed to various pinning mechanisms for the grain boundaries, or to a reduction in the grain-boundary energy due to solute segregation, which can reduce the grain-boundary energy, resulting in a thermodynamically stable nanostructure. Accordingly, in this work we will shed light on the thermal stability and properties of various nanocrystalline metallic systems.

4:40 PM  
Thermal Stability and Grain-boundary Segregation in Al-Alloy Thin Films: Aashish Rohatgi1; Arun Devaraj1; Rama Vemuri1; Libor Kovarik1; Xiujuan Jiang1; Giridhar Nandipati1; Suveen Mathaudhu1; Wenbo Wang2; Jason Trelewicz2; 1Pacific Northwest National Laboratory; 2Stony Brook University
    The goal of our work is to identify structural alloy compositions that possess a thermally stable nanostructure that can, thus, take advantage of their nanostructure-driven superior mechanical properties at elevated temperatures as well. Recent literature has shown the possibility of using solute segregation at the grain boundaries as a means to achieve thermally stability of nano-grained materials against grain growth. Solute segregation is postulated to lower the grain boundary energy and hence, reduce the thermodynamic driving force for grain growth at elevated temperatures. In this work, we explore the feasibility of thermal stability in nanostructured Al-based alloys. Al-alloy thin films with different solute contents were fabricated by the sputtering technique. The sputtered thin films were subjected to elevated temperature annealing treatments for different durations and characterized by atom probe tomography, TEM and indentation. This presentation will describe the potential for solute segregation in Al alloys and its influence on grain-growth.

5:00 PM  
Enhanced Thermal Stability of Ultrafine-grained Aluminum Fabricated by Applying a Fast Cooling Rate after Hot Rolling: Pei-Ling Sun1; 1National Sun Yat-Sen University
    In this work, it is proved that a commercially pure aluminum with ultrafine-grained (UFG) structures can be fabricated in the industry. Aluminum was hot rolled, followed by subsequent fast cooling (water quenching, WQ) or slow cooling (furnace cooling, FC), and then cold rolled (CR). The WQ UFG Al exhibits an enhanced thermal stability due to an increase in concentration of solid solution atoms, relative to the FC one. Moreover, detailed microstructural characterization indicates that the WQ UFG Al has finer grain dimensions and an increased proportion of high-angle grain boundaries. X-ray pole figures measurements were performed on the CR and annealed specimens to obtain the macrotextures. Electron backscattered diffraction was employed to observe the microstructures and microtextures of these samples. The results reveal that annealing occurred in a way of grain coarsening and the rolling texture was retained in the WQ samples, while traditional recrystallization occurred in the FC samples.

5:20 PM  
Effects of Ultrafine Grain Structure on Al Alloy Response to Corrosive Environments: Troy Topping1; 1California State University, Sacramento
    Nanostructured aluminum metal matrix composite alloys demonstrate superior mechanical performance over their microcrystalline counterparts. This research presents the mechanical behavior of ultra-fine grained (UFG) and nanocrystalline (NC) materials fabricated via cryomilling, i.e. ball milling in a cryogenic slurry and subsequent consolidation by various thermomechanical (TMP) processing routes, and compares these materials to conventionally produced alloys. This overview encompasses recent development in synthesis and characterization of UFG and NC metallic and composite materials via cryomilling with particular emphasis on the following topics: influence of primary consolidation and secondary processing methods; microstructural evolution from nanostructured powders to consolidated, bulk materials; and mechanical behavior of consolidated materials in extreme environments. New research concerning the performance of UFG and NC material in corrosive environments is highlighted. A rationale for reported stress corrosion cracking behavior of cryomilled alloys will be discussed.

5:40 PM  
Evidence that Abnormal Grain Growth Precedes Fatigue-crack Initiation in Nanocrystalline Metals: Timothy Furnish1; Daniel Bufford1; Khalid Hattar1; Christopher O'Brien1; Stephen Foiles1; Apurva Mehta2; Douglas Van Campen2; Brad Boyce1; 1Sandia National Laboratories; 2SLAC National Accelerator Laboratory
    Nanocrystalline metals show a clear correlation between fatigue-induced abnormal grain growth (AGG) and crack initiation during high-cycle fatigue. However, whether AGG precedes crack initiation or occurs concurrently has only been speculated and is still unknown. In this study, we utilize in-situ synchrotron X-ray diffraction to detect AGG at various stages of the fatigue life. The high-cycle fatigue was intentionally interrupted following the detectable onset of AGG, but prior to final fracture, allowing for detailed surface and microstructural evaluation during this intermediate stage of the fatigue life. Our results reveal AGG and sub-grain formation and grain rotation well before crack initiation, highlighting AGG as a precursor for crack initiation during high cycle fatigue in nanocrystalline metals. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.