Ultrafine-grained and Heterostructured Materials (UFGH XI): Processing & Microstructure I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Caizhi Zhou, University of South Carolina; Megumi Kawasaki, Oregon State University; Enrique Lavernia, University of California, Irvine; Terry Lowe, Colorado School of Mines; Suveen Mathaudhu, Colorado School of Mines; Ruslan Valiev, UFA State Aviation Technical University; Yuntian Zhu, City University of Hong Kong
Monday 2:30 PM
February 24, 2020
Room: Marina Ballroom D
Location: Marriott Marquis Hotel
Session Chair: Erhard Schafler, University of Vienna; Kaka Ma, Colorado State University
2:30 PM Invited
Grain Refinement-induced Plasticity in Heterostructured Brass: Xiaolei Wu1; Yuntian Zhu2; 1Laboratory of Nonlinear Mechanics, Chinese Academy of Sciences; 2North Carolina State University
Grain refinement in metals has been extensively explored for improving strength, but seldom occurs during tensile deformation. Here we report dynamic grain refinement in heterostructured brass during tensile testing, which enabled high tensile plasticity (ductility), namely the grain refinement-induced plasticity (GRIP). The grain refinement was realized by forming nanograins via deformation twinning at grain boundaries, which produced sustained strain hardening to enhance ductility and facilitate plastic strains at grain boundaries. The GRIP effect may become another important strategy for designing strong and tough metals. GRIP may also exist in other heterostructured fcc alloys and some hcp metals of low SFE, which needs further investigation.
2:50 PM
Cu-Ta FCC-BCC Metal Composites Fabricated via Powder Consolidation by Equal Channel Angular Extrusion: Zachary Levin1; Michael Demkowicz1; K. Hartwig1; 1Department of Material Science and Engineering, Texas A&M University
Metal matrix composites composed of copper-tantalum were consolidated at room temperature from powder blends with the use of equal channel angular extrusion (ECAE). A total of five different processing routes were applied, with 1, 2 or 4 extrusions for each sample. The extrusion routes were selected in order to produce metal composites with elongated or equiaxed morphologies of the constituent phases. Samples were subsequently heat treated at copper homologous temperatures between 0.2 and 0.9. Mechanical behavior was characterized through hardness measurements and small-scale tension and compression tests under quasi-static conditions. This work was done to investigate the effectiveness of ECAE for powder consolidation as well as create model materials for investigating the impact of phase and grain boundaries on the mechanical behavior of FCC-BCC composites.
3:10 PM
Effect of High-pressure Torsion on Corrosion Behavior of a Magnesium ZK60 Alloy in 0.1M NaCl: Hamidreza Torbati-Sarraf1; Seyed Alireza Torbati Sarraf2; Terence Langdon3; 1Clemson University; 2University of Southern California; 3University of Southampton
This study aimed to investigate the corrosion behavior of a ZK60 magnesium alloy processed by various turn of High-pressure torsion (HPT). Extruded samples were processed through HPT up to 20 turns and the microstructures were evaluated using Electron back-scatter diffraction (EBSD). HPT processed samples were exposed to 0.1M NaCl solution and electrochemical responses were examined using polarization, EIS and hydrogen evolution tests. By increasing the numbers of HPT turns, more homogeneity with finer average grain sizes accompanied by the evolution of a nobler texture leads to an improved corrosion performance. Post-corrosion microscopic observations revealed improved protective layers after higher turns of HPT.
3:30 PM
Hierarchical Structures in Ti-6Al-4V by Thermohydrogen Refinement of Microstructure: Brady Butler1; Laura Moody2; Daniel Lewis3; Ion Powell3; Matthew Dunstan1; James Paramore1; 1United States Army Research Laboratory; 2Texas A&M University ; 3Texas A&M University
Ultrafine grained and hierarchical structures produced by thermomechanical means offer intriguing combinations of strength and ductility in a variety of metals. However, deformation processing is not typically suited to additive manufacturing (AM) and other near-net-shape (NNS) processing techniques. This study examines a novel process for heat treatment of titanium alloys in a hydrogen atmosphere, which leads to an ultrafine grained and inherently hierarchical microstructure without thermomechanical work. This thermohydrogen refinement of microstructure (THRM) process uses hydrogen as a temporary alloying addition to refine microstructure in Ti-6Al-4V components. The mechanisms of microstructural refinement are explored and characterized via orientation imaging microscopy. Mechanical properties are measured with miniaturized mechanical testing. Finally, these unique hierarchical microstructures are compared to conventional AM and wrought processed materials to determine the suitability of THRM as a post processing tool for NNS manufacturing of titanium.
3:50 PM Invited
Heterogeneous Pore Architecture Achieved by Spark Plasma Sintering: Alexander Preston1; Yuchen Lin1; Kaka Ma1; 1Colorado State University
Spark plasma sintering (SPS) is known for its capability of preserving ultrafine-grained (UFG) structure because of its rapid densification rate. While many studies on UFG materials aimed to minimize porosity to achieve a high relative density, forming porous structure became one trend of the powder metallurgy as pores reduce the weight of the materials and increase the surface area. In this presentation, recent efforts on the fabrication of porous materials via SPS are discussed, including literature review and our own research results on stainless steels and Ti. It is found partial densification and thermal gradients in SPS provide an opportunity to engineer a heterogeneous meso- and micro- pore architecture in the sintered materials. Reducing the pore size to the submicron regime improve strength and deformability. The discussion is emphasized on the effect of thermal gradients in SPS on the formation of inter-particle contacts and the consequent pore structure.
4:10 PM Break
4:30 PM Invited
Nanostructures and Properties of Rapid Directional Solidification of Al Alloys: Mohsen Asle Zaeem1; Sepideh Kavousi1; 1Colorado School of Mines
Rapid directional solidification is an important part of several manufacturing processes. Besides the overall importance of determining the processing-structure-property relations in manufacturing processes, study directional solidification can provide important insights into the fundamentals of instabilities at the solid-liquid interfaces which result in complex nano/microstructures (e.g., dendrites). In this work, to overcome the difficulty of experiments in direct observation of nano/microstructural evolution during solidification of metals and alloys, we present a large scale molecular dynamics (MD) simulation framework based on the second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potentials to study nanostructures that form during the rapid solidification. Several solidification heterogeneities and defects such as twins, stacking faults, and second phase precipitates are detected to form in different Al alloys. These heterogeneities are determined to significantly affect the crystal growth during rapid directional solidification, as well as the nanostructures and properties of solidified alloys.
4:50 PM
Atomistic Analysis of the Effect of Internal Defects on the Deformation of Nanocrystalline Metals: Caizhi Zhou1; Sixie Huang1; 1Missouri University of Science and Technology
Nanocrystalline (NC) metals normally process ultrahigh strength in comparison to the coarse-grained counterparts. While the fracture strain of most NC metals, such as copper and nickel, is usually less than 5% due to the limited space for dislocation accumulation inside the grains, and voids and cracks are preferred to nucleate at grain boundaries after yielding. Adding defects inside the nano grains is one strategy to minimize the trade-off of strength versus ductility. In this work, we aim to understand the effect of different types of internal defects (nano-domain and Frank-Read source) on the crack nucleation in NC metals by molecular dynamics simulations. We compare the in stress-strain responses of pristine and defected NC metals. We also analyze the internal stress on the grain boundary atoms, dislocation density evolution, void volume fraction evolution and plastic contribution from dislocation or grain boundaries activities.
5:10 PM Cancelled
In-situ Synchrotron X-ray Profile Analysis during High Pressure Torsion: Erhard Schafler1; Michael Kerber1; Florian Spieckermann2; Roman Schuster3; Torben Fischer4; 1University of Vienna; 2University of Leoben; 3University of Technology Vienna; 4Helmholtz-Zentrum Geesthacht
X-Ray Line Profile Analysis is a powerful method to characterize the microstructure of deformed materials, especially when high energy and brilliant Synchrotron radiation enables investigations with high time and spatial resolution. Parameters like dislocation density, dislocation arrangement as well as scattering domain size and it's distribution are parameters of a physical model of peak broadening, which can be applied to high quality diffraction measurements. A small sample high-pressure-torsion-machine was designed in order to perform in-situ diffraction experiments during the deformation process at hydrostatic pressures up to 8GPa in order to follow the strain as well as pressure induced microstructural characteristics of any material deformed. This was possible with the ideal design and equipment at the High-Energy-Materials-Science-beamline at PETRA III in Hamburg. Recent and first results of experiments on HPT-deformed Ni, Ti and HEAs are presented.
5:30 PM
Mechanical Properties and Microstructure Evolution of Multilayered Al-Cu Hybrid Materials Produced by High-pressure Torsion: Piotr Bazarnik1; Barbara Romelczyk-Baishya1; Jiaoyan Dai2; Yi Huang3; Małgorzata Lewandowska1; Terence Langdon3; 1Warsaw University of Technology; 2Institute of Materials, Ningbo University of Technology; 3University of Southampton
High-pressure torsion (HPT) was used to produce nanostructured multilayered hybrid Al-Cu systems. Three-layered blocks of Al/Cu/Al and Cu/Al/Cu were subjected to up to 200 revolutions of HPT. Both systems were examined by X-ray diffraction, scanning and transmission electron microscopy (SEM-TEM), energy dispersive spectrometry (EDX), microhardness measurements and tensile tests. The SEM and TEM observations revealed the formation of nano-layered structures in both configurations but they differed significantly in terms of grain size, which was smaller for the Al/Cu/Al system. XRD and selected area electron diffraction (SAED) analysis confirmed the formation of intermetallic CuAl2 and Cu9Al4 phases, whose fraction was higher for the Al/Cu/Al system. Higher microhardness (500 Hv) was obtained for the Al/Cu/Al system. The results demonstrate that HPT offers a significant opportunity for producing novel nanostructured Al-Cu multilayered composites with unique mechanical properties.
5:50 PM Cancelled
Kinetic Path Dependent Thermal Stability of Copper after Severe Plastic Deformation: Jing Tao Wang1; 1Nanjing University of Science & Technology
Thermal stability of copper after severe plastic deformation, was investigated by annealing and microhardness and microstructure characterization. Equal-Channel Angular Pressing with or without backpressure, and High-Pressure Torsion were used to process the copper until the microstructure is saturated and no further refinement can be achieved by each of the processing route. Thermal stability of the samples, indicated by the peak decreasing rate of microhardness upon annealing temperature, and the corresponding temperature of this peak, was plotted vs stored energy for the samples processed by different deformation routes. In comparison to Equal-Channel Angular Pressing with or without backpressure, samples processed by High-pressure torsion, which owns the highest stored energy because of its most refined grain size among the samples processed by the three different routes, exhibit the highest thermal stability. This is against the conventional viewpoint of lower thermal stability of materials with higher stored energy after deformation processing.