By analyzing the problem of high pressure torsion (HPT) in the rigid plastic formulation, we show that the power hardening law of plastically deformed materials leads to self-similarity of HPT, admitting a simple mathematical description...
moreBy analyzing the problem of high pressure torsion (HPT) in the rigid plastic formulation, we show that the power hardening law of plastically deformed materials leads to self-similarity of HPT, admitting a simple mathematical description of the process. The analysis shows that the main parameters of HPT are proportional to β (q) , with β being the angle of the anvil rotation. The meaning of the parameter q is: q = 0 for velocity and strain rate, q = 1 for shear strain and von Mises strain, q = n for stress, pressure and torque (n is the exponent of a power hardening law). We conclude that if the hardening law is a power law in a rotation interval β, self-similar regimes can emerge in HPT if the friction with the lateral wall of the die is not too high. In these intervals a simple mathematical description can be applied based on self-similarity. Outside these ranges, the plasticity problem still has to be solved for each value of β. The results obtained have important practical implications for the proper design and analysis of HPT experiments.
The nanostructure and the carbon distribution in a pearlitic steel processed by torsion under high pressure was investigated by three-dimensional atom probe. In the early stage of deformation (shear strain of 62), off-stoichiometry...
moreThe nanostructure and the carbon distribution in a pearlitic steel processed by torsion under high pressure was investigated by three-dimensional atom probe. In the early stage of deformation (shear strain of 62), off-stoichiometry cementite was analysed close to interphase boundaries and a strong segregation of carbon atoms along dislocation cell boundaries was observed in the ferrite. At a shear strain of 300, only few nanoscaled off-stoichiometry cementite particles remain and a nanoscaled equiaxed grain structure with a grain size of about 20 nm was revealed. 3D-AP data clearly point out a strong segregation of carbon atoms along grain boundaries. The influence of this carbon atom segregation on the nanostructure formation is discussed and a scenario accounting for the nanocrystallisation during severe plastic deformation is proposed.
... 12, 450000 Ufa, Russia 3Institut für Mikro-und Nanomaterialien, Universität Ulm, Albert-Einstein-Allee 47, 89081 Ulm, Germany
ajiangli.ning@kit.edu,
bjulia.ivanisenko@kit.edu Keywords: ferritic-pearlitic steel; HPT; homogeneous nanostructure; cementite decomposition ...
ABSTRACT Because of its great importance in modern engineering and technology applications, steel continues to be highly relevant in the modern research field of nanocrystalline materials. Innovative processing methods and procedures are...
moreABSTRACT Because of its great importance in modern engineering and technology applications, steel continues to be highly relevant in the modern research field of nanocrystalline materials. Innovative processing methods and procedures are required for the production of such materials, which possess superior properties compared to their conventional counter parts. In this research, the original microstructure of a commercial C45 steel (Fe, 0.42–0.5 wt% C, 0.5–0.8 wt% Mn) was modified from ferritic–pearlitic to bainitic. Warm high pressure torsion for 5 rotations at 6 GPa and 350 °C was used to process the bainitic sample leading to an ultrafine/nano-scale grain size. A unique nano-crystalline microstructure consisting of equiaxed and elongated ferrite grains with a mean size smaller than 150 nm appeared in images taken by Transmission Electron Microscopy. Results of in-situ tensile testing in a scanning electron microscope showed very high tensile strength, on the order of 2100 MPa with a total elongation of 4.5% in comparison with 800 MPa and around 16% in the original state. Fracture occurred abruptly, without any sign of necking, and was typically caused by the stress concentration at a surface flaw. Also, stress concentrations near all surface defects were observed on the sample, visualized by the formation of shear bands. The fracture surface was covered with dimples, indicating ductile fracture. These properties are fully comparable with high strength, high alloyed steels.
ABSTRACT Understanding the deformation behavior of nanocrystalline (nc) materials is important because of their possible application as structural materials. The investiga-tion of macroscopic nc samples during in situ mechanical tests can...
moreABSTRACT Understanding the deformation behavior of nanocrystalline (nc) materials is important because of their possible application as structural materials. The investiga-tion of macroscopic nc samples during in situ mechanical tests can shed light on operating deformation mechanisms. For example, observations during a compression test in a scanning electron microscope (SEM) or results obtained by more localized methods like transmission electron microscopy can extend our knowledge on this subject. In this study, we present the results of in situ SEM com-pression tests on nc Pd–10 at.% Au alloy with a mean grain size of 23 nm produced using the combination of inert gas condensation with subsequent high-pressure torsion. We show that plastic flow in this material is very inhomoge-neous on both the macro and the mesoscale as it is local-ized in one area of the compression sample and within shear bands. The formation of shear bands is accompanied by strain softening. We propose that such behavior can be explained by the activation of grain boundary mediated deformation mechanisms instead of dislocation-based plasticity. This conclusion was supported by in situ syn-chrotron XRD measurements which revealed that no preferential grain orientation is forming during the com-pression of identically prepared samples of the same material.
Qingping Cao,a) Feng Xu, Jingwei Liu, Lianyi Chen, Xiaodong Wang, and JZ Jiangb) International Center for New-Structured Materials (ICNSM), Zhejiang University and Laboratory of New-Structured Materials, Department of Materials Science...
moreQingping Cao,a) Feng Xu, Jingwei Liu, Lianyi Chen, Xiaodong Wang, and JZ Jiangb) International Center for New-Structured Materials (ICNSM), Zhejiang University and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, ...
The aim of this investigation was to evaluate the microstructural change after laser welding and its effect on the tensile properties and strain hardening behavior of DP600 and DP980 dual-phase steels. Laser welding led to the formation...
moreThe aim of this investigation was to evaluate the microstructural change after laser welding and its effect on the tensile properties and strain hardening behavior of DP600 and DP980 dual-phase steels. Laser welding led to the formation of martensite and significant hardness rise in the fusion zone because of the fast cooling, but the presence of a soft zone in
ABSTRACT The suggested use of nanoporous gold for functional and structural applications requires uniform and specifically crack-free monolithic bodies, ideally with a structure size in the range of 10 nm or below. Here we investigate...
moreABSTRACT The suggested use of nanoporous gold for functional and structural applications requires uniform and specifically crack-free monolithic bodies, ideally with a structure size in the range of 10 nm or below. Here we investigate electrochemical dealloying of two different starting alloys, Au25Ag75 and Au25Cu75, as pathways towards that goal. With an emphasis on the processes that lead to crack formation, we discuss the role of the parameters (i) lattice parameter change, (ii) dealloying potential and rate, and (iii) thermo-mechanical treatment of the master alloys. The Cu-based alloys are found to give superior homogeneity at very small structure sizes, provided that intermediate temperature treatments are avoided. A complete suppression of crack formation was achieved by application of a dealloying potential of 1.1 V versus Ag/AgCl, at a ligament size of 11 nm.
... By Hai-Jun Jin,* Dominik Kramer, Yulia Ivanisenko and Jörg Weissmüller ... Some recent studies, including micro-pillar compression,[6] micro-tension,[7] micro-and nano-indentation,[811] show that the nanoporous Au (with relative...
more... By Hai-Jun Jin,* Dominik Kramer, Yulia Ivanisenko and Jörg Weissmüller ... Some recent studies, including micro-pillar compression,[6] micro-tension,[7] micro-and nano-indentation,[811] show that the nanoporous Au (with relative density below 40%) can be as strong as bulk ...
ABSTRACT An overview of the synthesis and processing techniques for bulk nanostructured materials that are based on “bottom-up” approaches is presented. Typically, these processes use nanoparticles, which can be produced by a variety of...
moreABSTRACT An overview of the synthesis and processing techniques for bulk nanostructured materials that are based on “bottom-up” approaches is presented. Typically, these processes use nanoparticles, which can be produced by a variety of methods in the gas, liquid or solid state, as the basic building blocks. Their assembly into bulk nanostructured materials requires at least one more processing step, such as compaction or the formation of thick films. For certain nanostructures, film deposition techniques can also be employed. A wide range of nanostructures – from thick films with theoretical density to bulk nanocrystalline materials with nanoporosity – exhibiting novel structural and functional properties useful in many fields of applications are presented. Additionally, the properties of these bulk nanostructured materials can be categorized as either tailored, i.e., microstructure-dependent and inherently irreversible, or tunable, i.e., reversible by the application of an external field. Examples of both categories of properties are presented and the special role of the synthesis and processing routes to achieve the necessary nanostructures is emphasized.
Aberration-corrected transmission electron microscopy was used to provide structural information on a triple junction in nanocrystalline Pd. This triple junction consists of two intersecting Σ3 twin boundaries with a Σ9 grain boundary and...
moreAberration-corrected transmission electron microscopy was used to provide structural information on a triple junction in nanocrystalline Pd. This triple junction consists of two intersecting Σ3 twin boundaries with a Σ9 grain boundary and is connected to a quadruple point via the Σ9 grain boundary. A comprehensive strain analysis of this triple junction using geometric phase analysis is presented and compared
... Author Contact Information , E-mail The Corresponding Author , Lilia Kurmanaeva a , Jörg Schmauch b , Harald Rösner c , Yulia Ivanisenko a ... In a model for the deformation mechanism, each individual nanoligament might be considered...
more... Author Contact Information , E-mail The Corresponding Author , Lilia Kurmanaeva a , Jörg Schmauch b , Harald Rösner c , Yulia Ivanisenko a ... In a model for the deformation mechanism, each individual nanoligament might be considered a free-standing pillar or wire, possibly ...