Ultrafine-grained and Heterostructured Materials (UFGH XI): Fundamentals & Processing
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Caizhi Zhou, University of South Carolina; Megumi Kawasaki, Oregon State University; Enrique Lavernia, University of California, Irvine; Terry Lowe, Colorado School of Mines; Suveen Mathaudhu, Colorado School of Mines; Ruslan Valiev, UFA State Aviation Technical University; Yuntian Zhu, City University of Hong Kong
Wednesday 2:00 PM
February 26, 2020
Room: Carlsbad
Location: Marriott Marquis Hotel
Session Chair: Kei Ameyama, Ritsumeikan University; Anton Hohenwarter, University of Leoben; Klaus-Dieter Liss, Guangdong Technion - Israel Institute of Technology; Megumi Kawasaki, Oregon State University
2:00 PM Invited
Role of UFG-shell Network on Improving Mechanical Properties in Harmonic Structure Materials: Kei Ameyama1; 1Ritsumeikan University
The Harmonic Structure (HS) is a heterogeneous microstructure with a spatial distribution of ultra-fine grains (UFG) and coarse grains (CG), that is, the CG areas (‘Core’) embedded in the matrix of three-dimensionally continuously connected network of UFG areas (‘Shell’). The HS materials such as pure-Ni, pure-Cu, austenitic stainless steels, etc, samples were fabricated by powder metallurgy route consisting of mechanical milling (MM) of the powders and subsequent sintering. It was found that the fraction of a “shell” area is an important parameter controlling the balance of the mechanical properties of the HS compacts. The HS with a higher fraction of “shell” area demonstrated higher strength and approximately similar elongation as compared to the homogeneous samples and HS samples containing low shell fraction. Moreover, it is noteworthy that the strain hardening behaviour of HS samples strongly depends grain size gradient in the “shell” area.
2:20 PM Invited
Testing Old & New Ideas to Address Unresolved Questions in UFGs & Patterned Micro/Nano Structures
: Elias Aifantis1; Katerina Aifantis2; 1Aristotle University of Thessaloniki; 2University of Florida
Higher order gradients and stochasticity effects have already been incorporated in modeling pattern formation and size effects in manmade and naturemade materials. A review of such earlier developments on material mechanics modeling is given first. Then some new elements from fractional/fractal calculus and Tsallis non-extensive entropy statistical thermodynamics are introduced to deal with issues that is not possible to address with combined gradient-stochastic models and conventional Boltzmann-Gibbs statistical thermodynamics. Preliminary results on shear bands, stress-strain serrations, pattern formation and the strength-ductility competition are provided. Certain model analogies between living and nonliving systems are pointed out. Finally, the role of the aforementioned generalizations on extending classical interatomic/intermolecular potentials used in multiscale modeling, is discussed. Acknowledgements The lecture was delivered upon invitation of ECA on behalf of all participants I. Tsagrakis/I. Konstantopoulos/A. Sidiropoulos and A.C. Tsolakis/G. Petsos/O. Kapetanou/I.N. Nikolaidis in the HFRI projects MIS 5005134 and MIS 5045454 respectively. Useful discussions with K. Parisis and K.E. Aifantis are acknowledged. ReferencesE.C. Aifantis, A Concise Review of Gradient Models in Mechanics and Physics, Front. Phys. 7:239, 1 – 8 (2020); E.C. Aifantis, Internal length gradient (ILG) material mechanics across scales & disciplines, Adv. Appl. Mech. 49, 1-110 (2016); I. Tsagrakis, I. Konstantopoulos, A. Sidiropoulos and E.C. Aifantis, On certain applications of gradient nanochemomechanics: deformation and fracture of LIB and SGS, J. Mech. Behav. Mat. 28, 74–80 (2019); A.C. Tsolakis, G. Petsos, O. Kapetanou, I.N. Nikolaidis and E.C. Aifantis, Model analogies between pattern formation in deforming engineering materials & morphogenesis in ageing human brains, J. Mech. Behav. Mat. 28, 95–106 (2019).
2:40 PM
Fracture and Ductility of Nanostructured Molybdenum–copper Composites: Anton Hohenwarter1; Katharina Schwarz2; Julian Rosalie2; Stefan Wurster2; Reinhard Pippan2; 1University of Leoben; 2Erich Schmid Institute of Materials Science, Austrian Academy of Sciences
Mo–Cu alloys are nowadays frequently used in high-power electrical applications, such as heat-sinks. By means of severe plastic deformation such alloys can be transformed into high strength nanocomposites. With focus on the damage tolerance of such composites this alloy type provides the possibility to analyze the fracture behavior of an intrinsically brittle (Mo) and ductile (Cu) UFG materials. In this work the fracture behavior of liquid-metal infiltrated Cu30Mo70 subjected to high pressure torsion was investigated. Along with the grain refinement a re-orientation of the individual constituents parallel to the shear plane takes place having a strong impact on the fracture properties. The relation between the microstructural evolution and changes in the fracture behavior will be discussed. In addition, a comparison to existing results from other high strength materials, such as pearlitic as well as duplex steels is made.
3:00 PM
Strain-Rate Dependence of Flow Stress Hardened by Annealing and Softened by Deformation in Nanostructured Aluminum Processed by Accumulative Roll-Bonding: Takahiro Kunimine1; Si Gao2; Ryoichi Monzen1; Nobuhiro Tsuji2; 1Kanazawa University; 2Kyoto University
Nanostructured metals can be hardened by low-temperature annealing and softened by subsequent deformation. It has been reported that the decreased mobile-dislocation density caused by low-temperature annealing led to the hardening of the nanostructured materials. Here, we report on the strain-rate dependence of flow stress hardened by annealing and softened by subsequent deformation in nanostructured aluminum processed by accumulative roll-bonding (ARB). Strain-rate sensitivity and activation volume of the nanostructured aluminum with or without subsequent annealing were measured by stress relaxation tests. Deformation mechanisms for the phenomena of “hardening by annealing and softening by deformation” in the nanostructured aluminum were discussed based on the experimental results in terms of thermally activated dislocation process. To explain the phenomena, an analysis was attempted with the combination of the Taylor-type dislocation strengthening model and the dislocation bow-out model from grain boundary, which was proposed for yield stress in ultrafine-grained and nanocrystalline metals.
3:20 PM Break
3:40 PM Invited
Synchrotron X-ray and Neutron Diffraction – Opportunities for Ultrafine-grained and Hetero-structured Materials: Klaus-Dieter Liss1; 1Guangdong Technion - Israel Institute of Technology (GTIIT)
In-situ neutron and synchrotron X-ray diffraction deliver unique insights into the microstructural evolution of metals under exotic conditions. Comprehensive exploitation of scattering signals include multi-dimensional reciprocal-space studies on a number of individual grains and local information. For each constituting phase, their statistics and temporal behavior reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, and twinning. As grains become ultra-fine, such individual grain information is lost, however opportunities exist to work with finer beams. They can reveal local information in heterogeneous materials, such as phase composition, lattice parameters, strain, texture, crystalline disorder etc. This presentation reviews examples on heat treatment after severe plastic deformation, global and local texture, and mechanically induced phase transformation while future potential for such characterization and development is risen.
4:00 PM
Synthesis of an Ultrafine-grained Metastable Al Alloy through Mechanical Bonding by High-pressure Torsion: Megumi Kawasaki1; Jae-Kyung Han1; Terence Langdon2; 1Oregon State University; 2University of Southampton
Processing by high-pressure torsion (HPT), which was developed initially as a grain refinement technique, was extended recently to the mechanical bonding of dissimilar metals. In this study, separate disks of Al and Mg were mechanically bonded by HPT up to 100 turns at 6.0 GPa. A series of experiments revealed that such high straining through HPT processing introduced an ultrafine-grained metastable Al alloy with grain sizes of ~35-40 nm in a state of supersaturated solid solution with a maximum Mg solubility of ~38.5 at.%. A superhard Al solid solution with a maximum Vickers microhardness value of ~370 was observed consistently across the disk diameter. Our results demonstrate the synthesis of a bulk nanocrystalline metastable alloy with good microstructural stability at room temperature where such bulk solids are not yet reported for mechanical alloying by powder metallurgy.
4:20 PM
The Influence of Severe Plastic Deformation on Phase Transformations in a Metastable Beta Titanium Alloy Ti15Mo: Milos Janecek1; Kristina Bartha1; Josef Strasky1; Anna Veverkova2; Pere Barrioberro Vila3; Jozef Vesely1; Peter Minarik1; Jakub Cizek1; Irina Semenova2; Veronika Polyakova2; 1Charles University; 2Ufa State Aviation Technical University; 3German Aerospace Center
A Ti15Mo, which is a representative of a simple binary metastable beta Ti alloy, in a beta solution treated condition was subjected to severe plastic deformation (SPD). Equal channel angular pressing (ECAP) and high pressure torsion (HPT) were employed to introduce a high density of lattice defects to the material. The material was subsequently subjected to several types of thermal treatments in order to examine the phase transformations occurring in the deformed material upon heating. In order to achieve a material with required mechanical properties, the effects of the grain boundaries, dislocations, induced strain, ω-phase and local chemical inhomogeneities on phase transformations were examined in-situ by electrical resistivity and synchrotron X-ray diffraction and complemented by post mortem detail investigation of the microstructure and lattice defects in characteristic conditions by scanning and transmission electron microscopy including advanced techniques of transmission Kikuchi diffraction and automated crystallographic orientation mapping and positron annihilation spectroscopy.
4:40 PM
Heterogeneous Lamella Phases Make 2205 Stainless Steel with Superior Strength and Ductility: Peiqing La1; Yu Shi1; 1Lanzhou University of Technology
Grain refinement to nanoscale can make the conventional steels several times stronger, but invariably leads to poor ductility. Here we demonstrate a lamellar dual-phase heterogeneous nanostructure in 2205 stainless steel synthesized by aluminothermic reaction and followed hot rolling that produced a superior yield strength of 780MPa, ultimate tensile strength of 990 MPa and an elongation of 54.6% at room temperature. The elongation is the highest in the reported duplex stainless steels with that level of strength. The product of tensile strength and elongation exceeds 50 GPa% and is the highest value for all of the steels that was reported in the literatures. The steel consists of heterogeneous lamellar ferrite phase and austenitic phase. The high strength is attributed to strengthening of high back stress arising form hierarchical and laminated dual-phase heterogeneous structure and distribution. The unusual high ductility originates from back-stress hardening and dislocation hardening.