Pan American Materials Congress: Nanocrystalline and Ultra-fine Grain Materials and Bulk Metallic Glasses: Phase, Interface and Crystalline Defects Evolution during SPD
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: Marina F
Location: Marriott Marquis Hotel

Session Chair: Ruslan Valiev, Ufa State Aviation Technical University; Gerhard Wilde, University of Muenster

2:00 PM  
Ultrafine Grain Structure and Thermal Stability of Al-Fe Alloys Processed by Severe Plastic Deformation: Amandine Duchaussoy1; Xavier Sauvage1; Kaveh Edalati2; Zenji Horita2; Gilles Renou3; Alexis Deschamps3; Frédéric De Geuser3; 1Normandy University; 2WPI, International Institute for Carbon-Neutral Energy Research; 3Univ. Grenoble Alpes, SIMAP
    Al-1%Fe and al-2%Fe alloys with a relatively large volume fraction of metastable Al6Fe intermetallic particles have been cast and then processed by high-pressure torsion (HPT). The severe plastic deformation induced grain refinement and particle fragmentation has been investigated using XRD, SEM, TEM and APT. Our results unambiguously show that Al6Fe particles are progressively fragmented down to the nanometer scale and finally dissolve in the Al matrix forming a Fe super saturated solid solution. After aging at 150°C, the precipitation of new Fe rich nanoparticles leads to a significant hardening combined with a good thermal stability. The limited grain growth (typically about 200 nm after 1h at 250°C) is attributed to grain boundary pinning by Fe rich nanoscaled particles. The best properties were achieved for the highest level of deformation by HPT and the highest Fe content that provide the most concentrated super saturated solid solution.

2:20 PM  
Grain Boundary Structure and Diffusivity of Severely Strained Metals and Alloys: Gerhard Wilde1; 1University of Muenster
    Severe plastic deformation (SPD) has often been applied for refining the microstructure of polycrystalline materials down to the submicron grain size range, yielding bulk materials that are mostly free from porosity or contaminations of the internal interfaces. At the same time, such materials showed remarkable property modifications exceeding modifications due to the mere total area of internal interfaces. Thus, the presence of “deformation-modified” grain boundaries has been advocated and recently also shown experimentally.The present contribution summarizes recent experimental results based on microstructure analyses and local strain analyses with atomic-scale spatial resolution together with grain boundary diffusion measurements on different pure metals and binary alloys. Basic issues concerning the structure of grain boundaries and their property characteristics are addressed. Particular attention will be given to the correlations between SPD processing and microstructure development that appear to be inherent to the process and less dependent on the specific material.

2:40 PM  
Insights into Deformation Induced Grain Boundary Migration in Ultrafine-grained Metals: Oliver Renk1; Pradipta Ghosh1; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science
    The increased fraction of grain boundaries makes nanocrystalline or ultrafine-grained materials prone for grain growth during deformation. The high stresses applied to these materials are often thought to be responsible for grain boundary migration. We present a study on UFG fcc and bcc metals, synthesized by high pressure torsion, and subjected to a strain path change (coldrolling). The initial UFG samples showed elongated grain structures. In order to understand the effect of stress on grain boundary migration, samples were rolled along different directions, with the long grain axis parallel to the rolling direction and in a second set of samples parallel to the normal direction. Depending on crystal structure and grain orientation with respect to the rolling direction, substantially different hardness and structural evolution with increasing rolling strain was observed. This indicates grain boundary migration in UFG materials to be not entirely driven by the applied stress as often suggested.

3:00 PM  
A High Resolution X-ray Diffraction Line Profile Analysis of Mg-Ce and Mg-Nd Alloys after HPT Processing: Hiba Azzeddine1; Yousf Islem Bourezg2; Zdeneck Matej3; Yi Huang4; Djamel Bradai2; Terence G. Langdon4; 1University of M'sila; 2USTHB; 3Max IV Laboratory; 4University of Southampton
    The particle size, size distribution and dislocation density were determined in ultrafine-grained Mg-1.44Ce (wt.%) and Mg-1.43Nd (wt.%) alloys processed by high-pressure torsion at ambient temperature using high resolution X-ray diffraction line profile analysis (XRDLPA). The alloy samples were processed up to 1 and 10 turns and the X-ray line profile measurements were carried out in the reflection geometry with scanning 2D detector in the X-ray powder diffraction beamline 711 of the MAXLab Synchrotron in Lund, Sweden. In order to check any microstructure parameters gradient along the radius of the HPT discs, each sample was measured at 5 points in a line with distances from the center. Software for microstructure analysis from X-ray powder diffraction based on total pattern fitting and modelling (MStruct) was used. The results from XRDLPA were correlated to microhardness measurements at these selected positions and there was good agreement.

3:20 PM Break

3:40 PM  
Interface Phenomena in SPD-processed Nanomaterials: Ruslan Valiev1; Maxim Murashkin2; Dmitry Gunderov2; 1Laboratory for Mechanics of Bulk Nanomaterials, Saint Petersburg State University; 2Ufa State Aviation Technical University
    Recent studies demonstrate that different types of grain boundaries (low angle and high angle ones, special and random, equilibrium and non-equilibrium, and so on) can be formed in metallic materials using severe plastic deformation (SPD). In this work by variations of regimes and routes of SPD processing we show for several light alloys (Al, Mg and Ti) and steels the ability to produce ultrafine-grained materials with different grain boundaries, and study its effect on mechanical and functional properties. The report also considers the results of application of SPD techniques for processing the initially amorphous alloys, in which the nanoclustered structure can be formed by optimal regimes of SPD (pressure, temperature, strain rate, etc.). The formation of interfaces in the amorphous alloys considerably influences their mechanical properties. The nature of this phenomenon and its practical importance has been studied as well.

4:00 PM  
Outstanding Mechanical Properties of High-Pressure Torsion Processed Multiscale Clad Layer of Twinning Induced Plasticity Steel and Interstitial Free Steel: Hyoung Seop Kim1; 1POSTECH
    Clad materials composed of a twinning-induced plasticity (TWIP) steel core sheet with two interstitial free (IF) steel sheath layers are processed by high-pressure torsion (HPT) up to 1 turn under an applied pressure of 6 GPa. The HPT-processed clad materials demonstrate extraordinarily enhanced mechanical properties, showing high strength as well as very good ductility. Experimental studies reveal that the improvement of the mechanical properties originates from inhomogeneous strain imposed during the early HPT stages and two distinct hardening mechanisms of each layer: grain boundary hardening of the IF steel and deformation-twinning-induced hardening of the TWIP steel.

4:20 PM  
Bulk Nano Lamellar Materials by Severe Plastic Deformation: Fan Liu1; Sunkulp Goel1; Yue Wang1; Ya Ming Zhu1; Hao Yuan1; Jing Tao Wang1; 1Nanjing University of Science and Technology
    In the present work nano lamellar materials has been produced by severe plastic deformation. Microstructural and mechanical characterization of the nano lamellar material has been performed by EBSD, TEM and tensile test. Bulk nano lamellar structure with an average thickness 40~90 nm of each lamella has been observed. The EBSD results show the presence of large fraction of high angle grain boundary. A bulk nano lamellar sheet of 1.2 mm thickness has been obtained after severe plastic deformation technique. The initial grain size of as received material has been 100 µm or larger. The tensile test reveals the enhancement of tensile strength to over 1 GPa for Nickle and Tantalum after SPD processing.

4:40 PM  
Thermal Stability of Defect Structure and Phase Composition in Ultrafine-grained 316L Stainless Steel Processed by High-pressure Torsion: Moustafa El-Tahawy1; Jenő Gubicza1; Yi Huang2; Hyelim Choi3; Heeman Choe3; János Lábár4; Terence Langdon2; 1Eötvös Loránd University; 2University of Southampton; 3Kookmin University; 4Centre for Energy Research, Hungarian Academy of Sciences
    The thermal stability of ultrafine-grained (UFG) microstructure in 316L stainless steel processed by High-Pressure Torsion (HPT) was investigated by differential scanning calorimetry (DSC) up to 1000 K. In the DSC thermograms two peaks were observed. The first, exothermic peak is related to the annihilation of vacancies and dislocations. During this recovery, the phase composition and the average grain size were practically unchanged. The activation energy of recovery was determined from the variation of DSC peak temperature versus heating rate. The second, endothermic peak was caused by a reverse transformation of alpha-prime martensite to gamma-austenite, however in this temperature range dislocation annihilation and a grain growth from 45 to 195 nm also occurred. It was concluded that the hardness of the annealed samples is mainly determined by the grain size. The combination of HPT processing and annealing at 1000 K resulted in an UFG gamma-austenite with high hardness of 4900 MPa.

5:00 PM  
Mechanical Properties of Laminated Titanium-Aluminum-Composites Processed by Accumulative Roll Bonding: Christopher Schunk1; Heinz Werner Höppel1; Mathias Göken1; 1Friedrich-Alexander Universität Erlangen-Nürnberg
    Laminated metallic composites with an ultrafine-grain (UFG) structure can be successfully produced by accumulative-roll-bonding (ARB). Due to the ARB-process, the stacking sequence and the layer thickness of the laminates can be varied and thus tailored properties with a high potential for light-weight applications can be achieved. In these micro- and nanostructured laminated metallic composites, the strength of the material is further increased by super-composed effects of the additional interfaces in the laminates. It is shown on the example of titanium-aluminum-laminates that the mechanical properties don’t obey a linear rule of mixture. The high strength of titanium and the low density of aluminum were combined and extraordinary high specific strength was achieved. The strength of the laminate is close to the strength of the titanium while the overall density is lower. Microhardness testing, X-Ray diffraction and STEM near the bonding layers were used to investigate the reason for this extraordinary performance.