Pan American Materials Congress: Nanocrystalline and Ultra-fine Grain Materials and Bulk Metallic Glasses: Mechanical Properties of Structural Materials Processed by 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

Tuesday 3:40 PM
February 28, 2017
Room: Marina F
Location: Marriott Marquis Hotel

Session Chair: Megumi Kawasaki, Hanyang University; Malgorzata Lewandowska, Warsaw University of Technology

3:40 PM  
Effects on Hardness and Microstructure of AISI 1020 Low Carbon Steel Subjected to High-Pressure Torsion Process: Diana Marulanda1; Hernando Jimenez1; Jittraporn Wonsa-Ngam2; Terence Langdon3; 1Universidad Antonio Nari˝o; 2King Mongkut’s Institute of Technology Ladkrabang; 3University of Southampton
    Low carbon AISI 1020 steel was subjected to high-pressure torsion (HPT) process at room temperature under a pressure of 6 GPa through ╝, 1, 2 and 5 turns. The microstructure evolution of the samples in each turn was studied using Scanning Electron Microscopy (SEM) and the variation in micro-strain, crystallite size and lattice parameter was analyzed using X-Ray Diffraction (XRD). The microhardness behavior across the samples diameter was measured using Vickers testing.

4:00 PM  
Static and Cyclic Mechanical Properties of High Strength Pearlitic Steels: Marlene Kapp1; Anton Hohenwarter2; Bo Yang1; Reinhard Pippan1; 1Erich Schmid Institute of Materials Science; 2Montanuniversitńt Leoben
    High pressure torsion was applied to a pearlitic steel, generating a high strength composite by refining the ferrite and cementite lamellae spacing to the nanoscale. Static mechanical properties have been studied by in-situ micro compression experiments inside a scanning electron microscope, which allows for an instructive correlation to the deformation and failure behavior. A compressive strength of 3.7 GPa was achieved for the nanocomposite, which could be explained by a distinct increase of the yield strength and strain hardening capacity compared to the initial material. Different types of strain localization were observed depending on the loading direction of the lamellae, ceasing the remarkable strain hardening capacity inherent to nanocomposites. The high static strength suggests an outstanding performance under cyclic loading conditions. Therefore, first results of cyclic micro bending experiments will be presented capable of shedding light onto the prevailing fatigue and damage mechanisms in these ultrastrong material.

4:20 PM  
The Influence of Testing Temperature on the Fracture Behavior of SPD-processed Iron and Tantalum: Anton Hohenwarter1; 1Department of Materials Physics, Montanuniversitńt Leoben, Austria
    The suitability of high strength ultrafine- and nanocrystalline materials processed by severe plastic deformation methods and aimed to be used for structural applications will strongly depend on their resistance against crack growth. Beside parameters such as grain size and specimen orientation the testing temperature is thought to have a great impact on the fracture toughness. Especially in body-centered cubic (bcc) metals the presence of a ductile to brittle transition causes the fracture resistance to be strongly temperature dependent. In this contribution the fracture behavior of two bcc-metals namely iron and tantalum will be in the focus. Both metals were processed by high pressure torsion to obtain an ultrafine microstructure and the fracture toughness was examined in a temperature range between -196░C and 200 ░C. In addition the influence of crack plane orientation was taken into account showing a large influence on the ductile to brittle transition.

4:40 PM  
Precipitation Processes and Related Strengthening Mechanisms in a Nanostructured 6082 Aluminium Alloy: Malgorzata Lewandowska1; Witold Chrominski1; 1Warsaw University of Technology
    In SPD processed ultrafine grained materials, precipitation processes are significantly affected by the high surface area of grain boundaries and local dislocation structure. In this work, a 6082 aluminium alloy was subjected to solution annealing, water quenching, hydrostatic extrusion (with accumulated total true strain of 4.6) and ageing at 100 and 160oC for various times. The microstructure after hydrostatic extrusion is inhomogeneous and depends on the grain orientation. Such local inhomogeneities strongly influence the precipitation processes. Homogeneous precipitation in grain interiors takes place only in microsized grains with dislocation substructure. In small grains surrounded with high angle grain boundaries, extensive precipitation at grain boundaries occurs with no precipitates in grain interiors. Based on quantitative microstructure evaluation, contributions of different strengthening mechanisms were estimated and compared to experimental results.

5:00 PM  
Strengthening Contributions on a Commercially Al-Mg-Si Alloy Processed by ECAP: Tarek Khelfa1; Mohamed Ali Rekik1; Jairo-Alberto Mu˝oz-Bola˝os2; Mohamed Khitouni1; Jose-Maria Cabrera2; 1University of Sfax; 2Universidad Politecnica de Catalunya
    The evolution of the microstructure and the mechanical response of an AA6060 alloy subjected to severe plastic deformation by ECAP has been studied. Samples were deformed in a 90║ die from 1 to 12 passes at room temperature following route Bc. The microstructure was evaluated by means of EBSD. Since During the first ECAP pass, the microstructure developed a large fraction of low angle boundaries associated with subgrain formation. A heterogeneous ultra-fine grain structure with an average grain size of 0.57 Ám and 0.47 Ám was obtained after 8 and 12 passes, respectively. Significant increases in hardness and tensile strength were observed since the first pass. The dependence of the yield stress on deformation and Mg content was evaluated in terms of the Hall–Petch effect, dislocation density, solid solution and precipitation strengthening.

5:20 PM  
Effect of Grain Size on Strain Rate Dependence of Mechanical Properties in CP Ti: Ying Chun Wang1; Alexander Zhilyaev2; Shukui Li1; Terence Langdon3; 1School of Materials Science and Engineering,Beijing Institute of Technology;National Key Laboratory of Science and Technology on Materials under Shock and Impact; 2Institute for Problems of Metals Superplasticity, Russian Academy of Sciences;Research Laboratory for Mechanics of New Nanomaterials, St. Petersburg State Polytechnical University; 3Materials Research Group, Faculty of Engineering and the Environment, University of Southampton
    The effect of grain size on stain rate dependence of compressive mechanical properties of commercial purity (CP) Ti was investigated. Tests were performed at room temperature using grain sizes from coarse-grained CG (20 m) to ultrafine-grained UFG (500 nm) and nanocrystalline NC (90 nm) with testing strain rates in the range from 10-2 to 103 s-1. The results show the flow stress and the strain rate sensitivity of CP Ti increase with decreasing grain size. The compressive yield strength versus grain size relationship follows the conventional Hall-Petch relationship at different strain rates. Moreover, the coefficients σ0 and k in the Hall-Petch equation are also strain rate dependent.