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

Wednesday 10:10 AM
March 1, 2017
Room: Marina F
Location: Marriott Marquis Hotel

Session Chair: Shima Sabbaghianrad, University of Southern California; Laszlo Toth, Université de Lorraine

10:10 AM  
Quantitative Modeling of Grain Fragmentation during Severe Plastic Deformation Featuring Grain Size Distribution, Texture, Strain Hardening, and Disorientation Distribution: Laszlo Toth1; 1Université de Lorraine
    A quantitative model was presented in 2010 by Toth et al. [Acta Materialia, 58 (2010) 1782] for predicting grain fragmentation during severe plastic deformation. The approach is based on the lattice rotation induced lattice curvature, thus, on the rotation of the crystals induced by the plastic strain. This model so far the most complete for predicting grain fragmentation because it is able to predict quantitatively in a single frame the evolution of the grain size distribution, the crystallographic texture, strain hardening, and disorientation angle (and axis) distribution. Several applications have proved the predictive capacity of the model. The present work report about the latest achievements of the lattice-curvature model and presents the software package which will be open for general use by the SPD community.

10:30 AM  
Continuous Dynamic Recovery in Pure Aluminum Deformed to High Strain by Accumulative Press Bonding: Sajjad Amirkhanlou1; Mostafa Ketabchi2; Nader Parvin3; Fernando Carreño4; 1Brunel University London; 2Amirkabir University of Technology ; 3Amirkabir University of Technology; 4CENIM-CSIC
    Microstructural evolution and mechanical properties of AA1050 aluminum alloy, prepared by accumulative press bonding, have been investigated by means of sophisticated analytical tools, including STEM and EBSD. The results revealed that continuous dynamic recovery was dominant mechanism in grain refinement, and resulted in formation of nano/ultrafine grains with average diameter of 450 nm in pressing direction and 320 nm in transverse direction. By increasing strain during APB process, the mean misorientation angle and the fraction of high angle boundaries increased and reached a saturation value of ~35˚ and ~78%, respectively. When strain increased during APB process, the tensile strength of the aluminum improved and reached 180 MPa after 14 cycles and the elongation dropped dramatically at the first cycle and then increased slightly. Strengthening in APB processed aluminum was attributed to strain hardening by dislocation accumulation dominant in primary cycles, and grain refinement which was dominant in final cycles.

10:50 AM  
Static Recrstallization and Grain Growth of Accumulative Roll Bonded Aluminium Laminates: Laura Lienshoeft1; Paul Chekhonin1; Juliane Scharnweber1; Tom Marr2; Tina Hausöl3; Heinz Werner Hoeppel3; Werner Skrotzki1; 1TU Dresden; 2IFW Dresden; 3Universität Erlangen-Nürnberg
    Aluminium laminates of high and technical purity layers were produced by accumulative roll bonding (ARB) at room temperture. To study the thermal stability, the laminates after 2 to 9 ARB cycles were annealed at 300°C and 400°C for one hour. The microstructure was analyzed by electron backscatter diffraction. The results show that for low ARB cycles and low annealing temperature the deformed technical pure layers start to recrystallize while the high purity coarse recrystallized layers experience intralayer grain growth. For higher cycles and higher annealing temperature the ultra-fine grained technical pure layers are consumed by layer overlapping growth of high purity grains producing a banded grain structure. For 9 ARB cycles a globular grain structure develops with grain sizes larger than twice the layer thickness. The effect of impurities on recrystallization and grain growth of ARB Al laminates will be discussed with regard to tailoring the ARB microstructure.

11:10 AM  
Evaluation of the Hardening and Softening Effects in Zn-21Al-2Cu with As Cast and Homogenized Microstructure Processed by Equal Channel Angular Pressing: Esperanza Elizabeth Martinez Flores1; Jose Luis Hernandez Rivera1; Jorge Garcia Rocha1; Jose de Jesus Cruz Rivera1; Gabriel Torres Villaseñor2; 1Instituto de Metalurgia-Universidad Autonoma de San Luis Potosi; 2Instituto de Investigaciones en Materiales-Universidad Nacional Autonoma de México
    In this work it is reported the evolution of the microstructure of the as-cast and homogenized Zn-21Al-2Cu samples, after 2 and 6 passes in an equal channel angular pressing (ECAP) at room temperature. A homogenization treatment for 24 h at 350 °C was applied in the as-cast samples and then they were deformed. An annealing heat treatment was made in all samples after ECAP process. One of the main results is that the homogenized and deformed samples showed a uniform fine-grained microstructure after annealing, while as-cast samples without annealing presented only some regions with fine-grained microstructure. The micro segregation level was higher in the as-cast samples in contrast to the homogenized ones even after annealing. Vickers microhardness measurement on samples after deformation is smaller than the original material indicating a softening, however after the annealing treatment

11:30 AM  
Microstructure Evolution of Ti-6Al-7Nb with Different Initial Microstructures Processed by High-Pressure Torsion: Jorge Cubero-Sesin1; Joaquin González-Hernández1; Elena Ulate-Kolitsky1; Stephen Petretti1; Luis Rojas-Morales1; José Vega-Baudrit2; Zenji Horita3; 1Instituto Tecnológico de Costa Rica; 2Laboratorio Nacional de Nanotecnología (LANOTEC-CeNAT); 3Kyushu University / I2CNER
    Ti-Al-Nb is one of the most recent metallic alloys for orthopedics because of a good combination of corrosion resistance, mechanical strength, biocompatibility and moderate Young’s Modulus. However, there are still few works on the microstructure evolution of this material by severe plastic deformation. The objective of this work is to study the evolution of microstructure of a Ti-6Al-7Nb alloy, with modification of the initial structure by heat treatment and subsequent processing at room temperature using High-Pressure Torsion (HPT). Vickers microhardness measurements were carried out on the surfaces of the disks and after preparation by metallographic etching, phase analyses were carried out by optical and scanning electron microscopy, as well as by X-ray diffraction. 3mm diameter disks were further thinned by twin-jet electropolishing for transmission electron microscopy, in order to observe the extent of grain refinement in the microstructures and explore the potential for further improvement in the properties aforementioned.

11:50 AM  
Limit of Grain Refinement after Processing by a Combination of Severe Plastic Deformation Techniques: Shima Sabbaghianrad1; Seyed Alireza Torbati-Sarraf1; Terence Langdon1; 1University of Southern California
    An Al-7075 aluminum alloy and a ZK60 magnesium alloy were processed by a combination of equal-channel angular pressing (ECAP) for 4 passes and high-pressure torsion (HPT) through total numbers of up to 20 turns. Processing by ECAP and HPT were performed at 473 K and room temperature, respectively. Mechanical tests revealed an increase in the hardness value of the Al-7075 alloy after the combination of ECAP and HPT. However, this value was decreased for the ZK60 magnesium alloy. Microstructural images of the Al-7075 alloy show significant grain refinement after a combination of ECAP and HPT compared to individual processing techniques. However, the average grain size in ZK60 alloy was larger after processing by the two-step SPD technique compared to only HPT processing. This investigation is focused on grain refinement for materials processed by a combination of ECAP and HPT.

12:10 PM  
Influence of SPD in Phase Transformation of Duplex Steels: Núria Llorca-Isern1; Isabel Lopez1; Jose Maria Cabrera2; Mohan Chand2; Irene Calliari3; Antoni Roca1; 1Universitat de Barcelona; 2Universitat Politècnica de Catalunya; 3Universita degli Studi di Padova
    Duplex and superduplex stainless steels allow high corrosion resistance and high mechanical strength. However these steels may suffer the formation of secondary brittle phases when they reach temperatures between 600C and 950C causing catastrophic service failure of components. In order to understand the influence of the mechanical history of the steel part, equal channel angular pressing was applied followed by different thermal treatments. Microstructural characterisation was carried out on the ecapped samples before and after themal treatment. The analysis of the hardness evolution of the same samples was also evaluated.