Pan American Materials Congress: Nanocrystalline and Ultra-fine Grain Materials and Bulk Metallic Glasses: Poster 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

Tuesday 5:30 PM
February 28, 2017
Room: Poster Area
Location: Marriott Marquis Hotel

PAN-51: Cyclic Closed-die Forming of Commercially Pure Cu at Room and Subzero Temperatures: Danielle Magalhães1; Allana Pratti1; Andrea Kliauga1; Benaque Rubert1; Vitor Sordi1; 1Federal University of São Carlos
    Cyclic closed-die forming (CCDF) is a process which allows applying large deformation levels by repetitive pressings operations, aiming for ultrafine and equiaxed grains, thus improving several properties of the material. A CCDF-die was designed and built to process pure Cu at room and cryogenic temperatures. Samples with dimensions of 10 x 10 x 20 mm3 were processed up to 6 passes, with inter-pass rotation, so that the sample returns to the initial dimensions after each pass. The intensity and homogeneity of plastic deformation was evaluated by mapping the Vickers hardness in the volume of the sample. Such hardness maps were compared to the strain distribution estimated by FEM numerical simulations. The deformed microstructures were observed by OM and TEM. It was demonstrated the effectiveness of cryo-CCDF in suppressing recovery mechanisms, thus resulting finer and more homogeneous microstructures in comparison with the similar room temperature process.

PAN-52: Direct Influence of Recovery Behaviour on Mechanical Properties in Oxygen-free Copper Processed Using Different SPD Techniques: HPT and ECAP: Meshal Alawadhi1; Yi Huang1; Terence Langdon1; 1University of Southampton
    Oxygen-free copper of 99.95 wt.% purity was severely deformed at room temperature by two modes of severe plastic deformation, equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). HPT was conducted through ½, 1 and 10 turns and ECAP was conducted through 4, 16 and 24 passes. The results show that dynamic recovery occurs during HPT and ECAP processing. Copper shows a faster recovery rate during HPT processing than ECAP. The influence of recovery behaviour on the mechanical properties was investigated using XRD, microhardness and tensile tests.

PAN-53: Wear Behavior of 2024 and 5083 Aluminum Alloys Processed by ECAP: M. Orozco Sandoval1; L. Guerra Fuentes2; R. Deaquino Lara3; M. A. L. Hernandez Rodriguez2; E. Garcia-Sanchez2; 1UANL; 2Universidad Autónoma de Nuevo León -Facultad de Ingeniería Mecánica y Eléctrica; 3Cinvestav Unidad Saltillo
    With the aim to study the effect of the severe plastic deformation on the wear properties, grain refinement and mechanical properties in aluminum alloys, in this work two commercial Al-Cu (2024) and Al-Mg (5083) alloy were deformed at room temperature by multi-pass 90º equal channel angular pressing (ECAP). Subsequently sliding wear test was undertaken in a ball on disk configuration under unlubricated conditions. The analysis of the wear behavior was performed with the characterization of the samples after processing and sliding tests using electron and optical microscopy, and microhardness tests. The wear response was modified at higher deformation conditions; the effect of the initial microstructure on the wear decreases with the level of strain in these alloys alloy. The sliding wear tests under unlubricated condition promote microstructural changes. The dominant wear mechanisms were identified and correlated with each microstructural condition.

PAN-54: Fatigue Response of ARMCO Iron after Deformation by Equal Channel Angular Pressing: Jairo-Alberto Muñoz-Bolaños1; Oscar-Fabian Higuera-Cobos2; Jose-Maria Cabrera1; 1Universidad Politecnica de Catalunya; 2Universidad del Atlántico
    The high cycle fatigue behavior of Armco iron severely deformed by ECAP at room temperature through route Bc until 8 passes, was studied and compared with the same material in the annealed state. The fatigue limit after ECAP processing increased by more than 250% rising from 274MPa to 717MPa. The microstructure was characterized by EBSD before and after the fatigue tests and it was observed in both sample an increment in the fraction of Low Angle Grain Boundaries at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was also done. This study shown a preferential orientation towards the γ fiber for both materials.

PAN-55: Hardness Evolution of AZ80 Magnesium Alloy Processed by HPT at Different Temperatures: Saad Alsubaie1; Yi Huang1; Terence Langdon1; 1University of Southampton
    Discs of an extruded AZ80 magnesium alloy were processed by high-pressure torsion (HPT) using 6.0 GPa up to 10 turns at different temperatures (296 and 473 K). The disc surfaces and cross-sectional planes were examined before and after processing using optical microscopy and Vickers microhardness (Hv). The microhardness results at the surface show differences in the strength of the material as a function of distance from the disc centres up to saturation as well as a function of distance from the bottom to the surface in the cross-sectional plane. This study analyses the effect of processing temperature on the evolution of microhardness of AZ80 magnesium alloy processed by high-pressure torsion.

PAN-56: Investigation on Activation Volume and Strain-rate Sensitivity in Ultrafine-grained Tantalum: Yue Wang1; Ying Liu1; Jing Tao Wang1; 1Nanjing University of Science and Technology
    The activation volume and strain-rate sensitivity(SRS) and their relationship are investigated. Through theoretical modeling based on the movement of both isolated kinks and kink pairs in a dislocation line, a new form of theoretical relationship between the SRS and activation volume was developed, which reduces to the conventional and frequently used form of the same relationship when SRS is approaching zero. The strain rate jump test during the necking stage of tensile testing process is validated through combined theoretical analytical approaches, for obtaining SRS of materials with short uniform tensile stage. To validate the theoretical approaches and modeling presented in this work, strain-rate jump tests and repeated stress relaxation experiments were conducted, to measure the SRS and activation volume of ultrafine-grained tantalum prepared by equal channel angular pressing. The experimental relationship between the SRS and the activation volume fits well with the new form of theoretical relationship.

PAN-57: Microestructural Characterization of a Asymmetric Accumulative Roll Bonded (AARB) AA1050 Aluminum: Renan de Godoi1; Felipe Almeida1; Vitor Sordi1; Andrea Madeira Kliauga1; 1UFSCar
    What distinguishes a particular SPD process from the others is the kind of viscoplastic flow and the deformation path. Processes with high level of shear and non-conservative deformation path, like ECAP, produce a quite random crystallographic distribution and lower anisotropy. However, ECAP is poorly suited for dealing with plate shaped samples and ARB alone induces the same texture as rolling; hence, an alternative can be found in the association of the asymmetric rolling technique to the ARB process, here named AARB. A laboratory rolling mill with a ratio of the roll diameters of 1.5 rotating at the same angular speed was employed to accumulative roll bond 1mm AA1050 aluminum sheets. This procedure was repeated 4 to 8 times with intermediate annealing treatments at 200oC for 15 min. The microstructure was analysed in the RD-TD plane by optical and TEM, texture and mesotexture was measured by EBSD .

PAN-58: Microstructure and Dynamic Mechanical Response of AA6061-T6 Processed by ECAP: Carlos Arturo Reyes Ruiz1; Chedly Braham2; Jose Maria Cabrera Marrero3; Nicolas Ranc2; Veronique Favier2; Gonzalo González1; 1Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México; 2Laboratoire Procédés et Ingénierie Mécanique et Matériaux, CNRS UMR 8006, ENSAM-CNAM; 3Universidad Politécnica de Cataluña
    The strength of an AA6061-T6 processed by ECAP up to six passes, under different strain rates (from 10-3 up to 103 s-1) was study. The characterization of quasi-static strain-rate test was performed in a universal testing machine, while the dynamic was carried out in a Hopkinson pressure bar. The correlation between the changes in the mechanical properties and the microstructure was assessed by means of electron microscopy. Under compression conditions, the material revealed a low strain-rate sensitivity, increasing the flow stress values as the strain rate increased. The flow stress at 0.1 plastic strain showed a remarkably improvement after one ECAP pass. It was found that such behavior was independent from the strain-rate regime and did not show any sign of reversibility. Finally, the microstructure observed shows that the dynamic strain rate response depends on the prior dislocation networks resulting from ECAP process.

PAN-59: Microstructure and Properties of Equal Channel Angular Extruded and Recrystallized OFHC Copper: Abhinav Srivastava1; Jason Springs1; Zach Levin1; Robert Barber2; Karl Hartwig1; 1Texas A&M University; 2Shear Form Inc.
    Oxygen free high conductivity copper (OFHC) is the best conductor material for non-superconducting high-field electromagnetic applications because of its low electrical resistivity. As-cast OFHC Cu has large grains which impart low strength and unwanted texture to the bulk material. The present work focuses on equal channel angular extrusion (ECAE) processing of OFHC Cu bars with one-inch square cross sections via different routes to obtain ultra-fine grains to maximize strength. Selected samples were also rolled after ECAE processing. The objective of this study is to provide information about strength, electrical resistivity, grain size, texture, and recrystallization behavior of heavily worked copper. Cu bars were annealed at 350°C prior to performing multiple extrusions at room temperature with strain intensity of 1.16 per pass. Processed bars were subsequently recrystallized. Microstructure and strength results are correlated with processing history. This study aims to provide better conducting materials information for high field magnet builders.