Ultrafine-grained and Heterostructured Materials (UFGH XI): Fundamentals
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
Tuesday 8:30 AM
February 25, 2020
Room: Marina Ballroom D
Location: Marriott Marquis Hotel
Session Chair: Ruslan Valiev, UFA State Aviation Technical University; Nobuhiro Tsuji, Kyoto University; Xiaoxu Huang, Chongqing University
8:30 AM Invited
Unravelling the Strengthening Effects of Strain Gradient and Back Stress on Heterogeneous Materials: Ting Zhu1; Yin Zhang1; 1Georgia Institute of Technology
Recent studies of gradient nanotwinned copper, 3D-printed stainless steel and several other heterogeneous materials raise a fundamental question on the role of strain gradient and back stress in controlling the mechanical behavior of these novel materials. Here we combine the mechanics modeling and experiment to unravel the strengthening effects of microstructural gradients and heterogeneities. Quantitative comparison is made between the experimental and modeling results for gradient nanotwinned copper and 3D-printed stainless steel. Our work reveals mechanistic connections between the plastic strain gradients and long-range back stresses that arise from processing- and deformation-induced microstructural heterogeneities. Insights are obtained to promote the strength-ductility synergy in the design of new heterogeneous microstructures.
8:50 AM Cancelled
Deformation Behavior and Strengthening Mechanisms of Ultrafine-Grained Al-2.5mass%Mg Alloy: Xiaodong Lan1; Si Gao1; Myeong-heom Park1; Akinobu Shibata1; Nobuhiro Tsuji1; 1Kyoto University
In the present study, fully recrystallized ultrafine-grained (UFG) Al-2.5mass%Mg specimens having various mean grain sizes were successfully fabricated by high-pressure torsion and subsequent annealing processes. Tensile test combined with digital image correlation (DIC) technique was performed to investigate the effect of grain size on the mechanical properties of the material. It was found that a transition from continuous yielding to discontinuous yielding occurred by changing the grain size from 0.2 to 9 µm. In addition, the serrated flow behavior, which is a well-known to exist in Al-Mg alloys, also exhibited a grain size dependence as characterized by the DIC analysis. Those results were compared with pure Al and the effects of grain size and Mg on the tensile behavior of the Al-2.5mass%Mg are discussed in terms of the Hall-Petch strengthening and the dynamic strain aging of Mg in Al.
9:10 AM
In-situ Neutron Diffraction Study on the Tensile Deformation of an Ultrafine-grained Fe-Ni-Al-C steel Including B2 Phase: Si Gao1; Wenqi Mao1; Wu Gong1; Stefanus Harjo2; Akinobu Shibata1; Nobuhiro Tsuji1; 1Kyoto University; 2J-PARC Center, Japan Atomic Energy Agency
In the present study, an Fe-24Ni-6Al-0.4C (wt%) specimen consists of ultrafine grained austenite and B2 phase was fabricated by simple cold rolling and subsequent annealing process, which showed excellent combination of tensile strength and elongation. In order to evaluate the contribution of each constituent phases, namely austenite, B2 and deformation induced martensite phase that was forming during tensile deformation, to the overall tensile flow stress of the material, tensile test with in-situ neutron diffraction measurement was conducted and the phase stress (elastic stress) of each constituent phase during tensile test was measured from the peak shifting in the neutron diffraction profiles. Significant phase stress was measured in B2 and martensite phase during tensile deformation, suggesting that both B2 phase and deformation induced martensite have major contributions to the high strength and high strain hardening of the material.
9:30 AM
Size Dependent Strengthening in High Strength Nanotwinned Al/Ti Multilayers: Yifan Zhang1; Sichuang Xue1; Qiang Li1; Jin Li1; Jie Ding1; Tongjun Niu1; Ruizhe Su1; Haiyan Wang1; Xinghang Zhang1; 1Purdue University
Here we report the study of magnetron-sputtered highly textured Al/Ti multilayers with various layer thicknesses (h = 1 - 90 nm). The hardness of Al/Ti multilayers increases monotonically with decreasing layer thickness without softening and exceeds 7 GPa, making it one of the strongest light-weight multilayer systems reported to date. High resolution transmission electron microscopy (TEM) and X-ray diffraction pole figure analyses confirm the formation of high-density nanotwins and 9R phase in Al layers. The density of nanotwins and stacking faults scales inversely with individual layer thickness. In addition, there is an HCP-to-FCC phase transformation of Ti when h ≤ 4.5 nm. And the post-indentation TEM analysis reveals deformation induced phase transformation in Ti layer. The high strength of Al/Ti multilayers primarily originates from incoherent interface, high-density twin boundaries, as well as stacking faults. Our findings have general implication for the design of high-strength and light-weight heterogeneous nanocomposite materials.
9:50 AM Invited
Enhanced Strength and Thermal Stability of Cu/Fe Nanolaminates: Mathias Goken1; Maher Ghanem1; Heinz Werner Höppel1; Benoit Merle1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg
Accumulative roll bonding, ARB is a very attractive process to combine different metals in multilayered nano-scaled composites for advanced functional and mechanical performance. By using the ARB process up to 14 cycles, Cu/Fe nanolaminates have been processed in quite large quantities with a layer thickness below 100 nm. The lamellar microstructure of these nano-scaled composites is quite homogeneous over the whole sample volume and is retained also after thermal annealing at more than 600 °C. This clearly shows that nano-materials with exceptional thermal stability have been obtained. Furthermore, also the strength of these nano-laminates is extraordinary. The strength increases, as it is well-known from all severe plastic deformation processes, in the first ARB cycles and later saturates after 6-8 cycles, where a minimum of the grain size is reached in bulk materials. The nano-laminates, however, show after 10-12 ARB cycles again a strong second regime of increasing strength, which is explained by extra grain-refinement, since the very small layer thickness also limits the maximum grain size.
10:10 AM Break
10:30 AM Invited
Understanding Deformation Behaviors of Laminated Al-AL2Cu Eutectic Alloy: Jian Wang1; 1University of Nebraska-Lincoln
Composites composed of alternate metal (soft) and intermetallic or ceramic (hard) lamellae can exhibit high strength, high strain hardening rate and measurable plasticity at room temperatures. Strain hardening develops in the soft phase, and high stress develops in the hard phase. The high stress in hard phase may trigger uniformly or localized shear (referred to as plastic co-deformation) or cracking in hard phase (referred to as failure). Cracks in hard phase initiate by the increased tensile stress due to loading transfer in tension test or bending induced tensile stress in compression test. These mechanical behaviors are strongly related to the plastic deformability and the layer thickness of the hard phase. Taking the Al-Cu eutectic alloy as an example, we demonstrated these deformation behaviors and corresponding mechanisms using multiscale experiments and modeling, and revealed unusual slip planes in hard Al2Cu phase and buckling occurrence at large compression but no cracking.
10:50 AM
Effect of Interface Type on the Deformation Behavior of Nanostructured Metals: Oliver Renk1; Verena Maier-Kiener2; Daniel Kiener2; Reinhard Pippan1; 1Erich Schmid Institute; 2Montanuniversität Leoben
Nanomaterials contain large fractions of interfaces which control mechanical properties and the deformation behavior. We present insights obtained from various nanocrystalline FCC materials by nanoindentation strain rate jump tests, revealing above a critical temperature a remarkable increase of the strain rate sensitivity. Comparing these transition temperatures with those obtained in an in-situ TEM study indicates, that the increased rate sensitivity is caused by a change from mechanically to thermally induced annihilation of lattice dislocations at the boundaries. The effect of this transition on mechanical properties will be evaluated. As for thermally activated dislocation annihilation interfacial diffusivity plays an important role, similar experiments were carried out on alloyed samples but also on samples containing different boundary types (twin, high and low angle boundaries) despite having the same interfacial spacing. These experiments reveal a fundamentally different mechanical behavior with temperature and suggest that strengthening is not solely determined by the boundary spacing.
11:10 AM Cancelled
Stabilizing Nano Grains of Pure Cu with Rapidly Heating Induced Grain Boundary Relaxation: Xiuyan Li1; Xin Zhou1; Ke Lu1; 1Institute of Metal Research, Chinese Academy of Sciences
The instability of nano grains in metals under thermal and mechanical stimuli limits the application and further grain refinement of nano grained metals. Although enhanced thermal stability can be obtained in nano grains below a critical grain size in metals produced by plastic deformation, the nano grains with size around the critical size or larger than it are still less stable than coarse grains but always inevitable. We discovered that the unstable nano grains with grain size of 60-180 nm in Cu produced from plastic deformation can be stabilized by heating up rapidly to a temperature higher than their grain coarsening temperatures. The notable thermal stability came from initiation of annealing twinning and resulting grain boundary relaxation.
11:30 AM
Grain Boundary Design of Nanostructured Metals with Superior Mutlifunctional Properties: Ruslan Valiev1; Nariman Enikeev1; Maxim Murashkin1; 1UFA State Aviation Technical University
This report presents the results of complex studies of the formation of different grain boundaries (low angle and high angle ones, special and random, equilibrium and non-equilibrium with strain-distorted structure as well as with the presence of grain boundary segregations and precipitations) in nanostructured materials processed using severe plastic deformation (SPD) with various regimes and routes. This entails the materials with superior multifunctional properties i.e. the combination of high mechanical and functional properties (corrosion and radiation resistance, electrical conductivity, etc.) that are induced by grain boundary design. Particular emphasis is laid on the physical nature and the use of multifunctional nanomaterials for their innovative applications in medicine and engineering.Acknowledgements: Research was funded by Ministry of Science and Higher Education of Russia (grant agreement 14.586.21.0061, UIN RFMEFI58618X0061).
11:50 AM Cancelled
Incompatible Plastic Deformation of Dual Gradient Nanotwinned Cu: Lei Lu1; 1Institute of Metal Research, Chinese Academy of Sciences
Dual-gradient nanotwinned (GNT) structure with a spatial gradient in both grain size and twin lamellar thickness, possessing extraordinary strengthening and work hardening, has opened an avenue towards understanding the gradient structure-related mechanical behavior. In this study, we investigated the incompatible plastic deformation of GNT Cu samples through the lateral strain and back stress . It is found that the incompatible plastic deformation exists in GNT Cu even at strains as small as ~1% and become more obviously with increasing the applied strains. Interestingly, the incompatible plastic deformation of GNT Cu becomes weaker at the same strain as the structural gradient increases.A much higher back stress is observed in GNT Cu, comparing to its homogeneous NT counterpart, and increases significantly with increasing structural gradient while the effective stress increases slightly. The result provides a better understanding of the build-in deformation mechanism of architect gradient structure.