Pan American Materials Congress: Nanocrystalline and Ultra-fine Grain Materials and Bulk Metallic Glasses: Student Session
Sponsored by: Third Pan American Materials Congress Organizing Committee
Program Organizers: Terence Langdon, University of Southern California; Megumi Kawasaki, Oregon State University; Roberto Figueiredo, Federal University of Minas Gerais; Jose-Maria Cabrera, Universidad Politecnica de Catalunya

Thursday 2:00 PM
March 2, 2017
Room: Balboa
Location: Marriott Marquis Hotel

Session Chair: Jose-Maria Cabrera, Universidad Politecnica de Catalunya; Yi Huang, University of Southampton

2:00 PM  
Microstructural Changes and Mechanical Behavior of AA6061 Al Alloy Severely Deformed at Cryogenic Temperatures: Danielle Magalhães1; Andrea Kliauga1; Vitor Sordi1; Maurizio Ferrante1; 1Federal University of São Carlos
    The combination of Severe Plastic Deformation (SPD) and cryogenic temperatures can be an efficient way to obtain metals and alloys with very refined microstructure and thus optimize the strength-ductility pair. However, there is still a lack of studies on cryogenic SPD process and their effects on microstructure and mechanical properties, especially in precipitation-hardenable aluminum alloys. This study describes the effect of low temperature processing in the microstructure, aging kinetic and tensile properties of AA6061 alloy after cryo-SPD. Samples of AA6061 alloy in solutionized state was processed by rolling and by Equal-channel Angular Presssing (ECAP) at a temperature range from 77 K to 123 K, for multiple passes to accumulate true strains up to 4.2. Results indicated that the aging kinetic is accelerated and the microstructure is more refined at cryogenic temperature. Thus, it is demonstrated the potential of cryo-SPD for improving microstructure and properties of the AA6061 alloy.

2:20 PM  
Examining the Microhardness Evolution and Thermal Stability of an Al-Mg-Sc Alloy Processed by High-pressure Torsion at a High Temperature: Pedro Henrique Pereira1; Yi Huang1; Terence Langdon1; 1Materials Research Group, Faculty of Engineering and the Environment, University of Southampton
    An Al-3%Mg-0.2%Sc alloy was solutionised and further processed by HPT at 450 K. Afterwards, samples subjected to 10 turns of HPT processing were annealed for 1 hour at temperatures ranging from 423 to 773 K and its mechanical properties and microstructural evolution were examined using microhardness measurements and EBSD analysis. The results demonstrate that HPT processing at an elevated temperature leads to a more uniform microhardness distribution as well as to an early saturation in the hardness values in the Al alloy compared with high-pressure torsion at room temperature. In addition, detailed EBSD analysis conducted on the HPT-processed samples immediately after annealing revealed that the Al-Mg-Sc alloy subjected to HPT processing at 450 K exhibits superior thermal stability by comparison with the same material subjected to HPT at 300 K.

2:40 PM  
Deformation-induced Formation of Supersaturated Solid Solutions in the Cu-Ag System: Karoline Kormout1; Pradipta Ghosh1; Verena Maier-Kiener2; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences; 2Department Physical Metallurgy and Materials Testing
    In the present study the key parameters controlling deformation-induced supersaturation in immiscible systems were systemically varied to quantify their effect on the degree of supersaturation by synchrotron X-ray measurements and make correlations to microstructural changes by transmission electron microscopy. For this purpose high-pressure torsion processing of initial micrometer sized powder mixtures (Cu-10/50/90wt%Ag) was performed to different applied strains and at various processing temperatures. It appeared that there is a transition from complete supersaturation to complete phase separation with increasing processing temperature, which surprisingly strongly depended on the composition. By studying the microstructural evolution as a function of applied strain, it was shown that a critical phase spacing of below 5 nm is needed to initiate the mixing process. At room temperature this was reached in Cu-10 and 90wt%Ag at applied strains of γ~750, while in Cu50wt%Ag strain localization in shear bands prevented complete supersaturation.

3:00 PM  
Nanomechanical Behavior of Precipitation-hardened Nanocrystalline High-entropy Alloy: Dong-Hyun Lee1; Moo-Young Seok1; Zhaoping Lu2; Jin-Yoo Suh3; Upadrasta Ramamurty4; Megumi Kawasaki1; Terence Langdon5; Jae-il Jang1; 1Hanyang University; 2University of Science and Technology Beijing; 3Korea Institute of Science and Technology; 4Indian Institute of Science; 5University of Southern California
    Recently, high-entropy alloys (HEAs) have emerged as a novel group of structural metallic materials exhibiting interesting mechanical behavior. Recent studies reported that the mechanical properties of HEAs can be further improved by grain refinement or precipitation hardening. Thus, one can expect a synergetic effect on mechanical performance by combining these two strengthening mechanisms. In this study, CoCrFeMnNi HEA was processed by high-pressure torsion and subsequent thermal treatments were performed to incorporate both advantages of nanocrystalline (nc) structure and precipitation. The mechanical behavior of precipitation-hardened nc HEA was investigated through nanoindentation tests with various pyramidal indenters. The obtained results were analyzed in terms of microstructural change underneath the indenter and variation in applied strains that can be controlled by changing indenter angle.

3:20 PM  
Defect Structure and Hardness in Ultrafine-grained Ni-Mo Alloys Processed by High Pressure Torsion: Garima Kapoor1; Yi Huang2; Terence Langdon2; V. Sarma3; Jenő Gubicza1; 1Eotvos Lorand University; 2University of Southampton, Southampton; 3Indian Institute of Technology Madras
    The purpose of this study was to investigate the effect of Mo content on the evolution of grain size, lattice defect structure and hardness during severe plastic deformation of Ni disks. Two Ni alloys with low (0.3 at.%) and high (5 at.%) solute Mo concentrations were processed by a combination of cryorolling and high pressure torsion (HPT). Experimental results obtained from X-ray line profile analysis, scanning electron microscopy and hardness measurements revealed that the higher Mo content yielded larger dislocation density and smaller grain size which caused higher hardness values after HPT. The smallest value of the grain size was about 100 nm, while the highest measured dislocation density was 60 x 10^14 m^-2. The gradient in hardness along the disk diameter was explained by the difference in grain size and dislocation density. The thermal stability of the microstructure was studied by differential scanning calorimetry.

3:40 PM Break

4:00 PM  
Wear Properties of Various Bulk Hybrid Materials Processed by High-pressure Torsion: Jae-Kyung Han1; Han-Joo Lee1; Daekuen Han1; Byungmin Ahn2; Megumi Kawasaki1; Terence Langdon3; 1Hanyang University; 2Ajou University; 3University of Southern California
    Wear resistance is one of the important functional properties in materials. In the present study, three different bulk hybrid nanomaterials were synthesized by using conventional high-pressure torsion (HPT) processing. The processed bulk hybrid metals were examined for evaluating the evolution of wear mechanisms and wear resistance. Tribological properties were investigated by using a reciprocal sliding tester for measuring the friction coefficient and wear properties which are tested through the worn scar analysis. The worn scar profiles were constructed by an optical interferometer and scanning electron microscope and the wear coefficient was calculated by the Archard equation. Together with additional supporting results from the hardness measurements and XRD analysis, there is a significant increase in the wear resistance in the bulk hybrid materials processed by HPT.

4:40 PM  
Fatigue Behavior of Friction Stir Processed Ultrafine Grained 5024 Al Alloy: Shivakant Shukla1; Mageshwari Komarasamy1; Rajiv Mishra1; 1University of North Texas
    Ultrafine-grained (UFG) microstructure in 5024Al alloy was produced via friction stir processing. The fatigue properties were investigated using fully reversible bending fatigue testing machine. Microstructural evolution during fatigue tests were analyzed by doing interrupted fatigue tests and subsequent orientation imaging microscopy (OIM) of the sample. In order to investigate the effect of grain size on the fatigue micro-mechanisms, three different grain sizes comprising of two UFG, and a coarse-grain materials were chosen. Particular emphasis was given to the role of grain size on the evolution of deformed structure and intergranular dislocation density. OIM was used to understand the preferable crack nucleation site based on Schmid Factor, dislocation density, and grain boundary character distribution. The fractured samples were inspected using scanning and transmission electron microscopes to understand the failure mechanism in UFG material.

4:20 PM  
Creep Deformation in Bulk Metallic Glasses: A Review : Kamia Smith1; Michael Kassner1; 1University of Southern California
    The creep properties of metallic glasses have not been extensively researched. Creep This presentation will review the creep literature relevant to metallic glasses. Bulk metallic glasses deform by means of “dislocation-like” defects, diffusional-type transformations and shear transformation zones (STZ); all which lead to relatively homogeneous flow upon applied loads at high temperatures. Homogenous flow has, even more recently, been observed at low temperatures. The current review of creep in amorphous metals will particularly focus on the aforementioned deformation mechanisms (STZ’s being the favorable one) by examining their time-temperature-transformation behaviors as well as examining descriptive classic creep-rate equations tailored to amorphous deformation. Inhomogeneity and anelasticity will also be discussed.

5:00 PM  Cancelled
Shock Compression Behavior of Ti-Based Monolithic Bulk Metallic Glass and its Composite: Rene Diaz1; Manny Gonzales1; Greg Kennedy1; David Scripka1; Ali Khosravani1; Surya Kalidindi1; Douglas Hofmann2; Naresh Thadhani1; 1Georgia Institute of Technology; 2NASA Jet Propulsion Laboratory
    Titanium-based multicomponent bulk metallic glass matrix composites (BMG-MCs) of varying crystallinity and monolithic bulk metallic glass (BMG) are investigated using uniaxial-strain plate-on-plate impact experiments to examine the effect of microstructure morphology on spall response under dynamic high pressure and high strain-rate deformation. BMG-MCs counteract the brittle nature of monolithic BMGs through in-situ formed crystalline dendrites which increase toughness and ductility. The dynamic compressive strength (Hugoniot Elastic Limit, HEL) and the tensile (spall) strength of the BMG-MC/BMG samples were determined using VISAR interferometry from experiments performed at varying impact velocities. Quantitative microstructural characterization was performed using stereological techniques and 2-point statistics to determine the role of size, morphology, and distribution of the crystalline dendritic phase on the dynamic mechanical behavior. The dynamic compressive and tensile yield strengths and damage response of the BMG/BMG-MCs at different impact conditions correlated with the varying microstructures will be presented.