The Mechanical Properties in the Vicinity of Grain Boundaries in Ultrafine-Grained and Polycrystalline Materials Studied by Nanoindentations

2004 ◽  
Vol 819 ◽  
Author(s):  
E. Schweitzer ◽  
K. Durst ◽  
D. Amberger ◽  
M. Göken
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundaries ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Polycrystalline Materials ◽  
Petch Relation ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Second Phases

AbstractThe strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

The Mechanical Properties in the Vicinity of Grain Boundaries in Ultrafine-Grained and Polycrystalline Materials Studied by Nanoindentations

2004 ◽  
Vol 821 ◽  
Author(s):  
E. Schweitzer ◽  
K. Durst ◽  
D. Amberger ◽  
M. Göken
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundaries ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Polycrystalline Materials ◽  
Petch Relation ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Second Phases

AbstractThe strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

Local Investigations of the Mechanical Properties of Ultrafine Grained Metals by Nanoindentations

2006 ◽  
Vol 503-504 ◽  
pp. 31-36 ◽  
Author(s):  
Johannes Mueller ◽  
Karsten Durst ◽  
Dorothea Amberger ◽  
Matthias Göken
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Room Temperature ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
Fcc Metals ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Indentation Strain

The mechanical properties of ultrafine-grained metals processed by equal channel angular pressing is investigated by nanoindentations in comparison with measurements on nanocrystalline nickel with a grain size between 20 and 400 nm produced by pulsed electrodeposition. Besides hardness and Young’s modulus measurements, the nanoindentation method allows also controlled experiments on the strain rate sensitivity, which are discussed in detail in this paper. Nanoindentation measurements can be performed at indentation strain rates between 10-3 s-1 and 0.1 s-1. Nanocrystalline and ultrafine-grained fcc metals as Al and Ni show a significant strain rate sensitivity at room temperature in comparison with conventional grain sized materials. In ultrafine-grained bcc Fe the strain rate sensitivity does not change significantly after severe plastic deformation. Inelastic effects are found during repeated unloading-loading experiments in nanoindentations.

Phase Mixture Models for Metallic Materials with Submicrometer Grain Size

2003 ◽  
Vol 791 ◽  
Author(s):  
Yuri Estrin ◽  
Hyoung Seop Kim ◽  
Mark Bush
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Mixture Models ◽  
Cell Walls ◽  
Mechanical Response ◽  
Metallic Materials ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Model Predictions ◽  
Phase Mixture

ABSTRACTPhase mixture models describing the mechanical properties of submicrometer grained metals are presented. In this approach, grain boundaries or cell walls are treated as a separate phase. Two cases are considered: the mechanical response of an ultrafine grained material and the process of grain refinement by equal channel angular pressing. Model predictions with regard to the evolution of the microstructure, strength and texture are verified for Cu.

Measurement of Bauschinger Effect in Ultrafine-Grained A1070 Aluminum Rods

2016 ◽  
Vol 725 ◽  
pp. 202-207 ◽  
Author(s):  
Takayuki Koizumi ◽  
Mitsutoshi Kuroda
Keyword(s):  
Grain Boundaries ◽  
Bauschinger Effect ◽  
Pure Aluminum ◽  
Circular Cross Section ◽  
Dislocation Motion ◽  
Uniaxial Tensile ◽  
Internal Stresses ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Compressive Tests

In this study, the Bauschinger effect in ultrafine-grained pure aluminum rods (A1070) was investigated. The samples were produced by multipass equal-channel angular pressing (ECAP) with ‘route BC’, which is known to give nearly equiaxial-shaped crystal grains. Dumbbell-shaped specimens with a circular cross section were machined from the samples subjected to ECAP to carry out uniaxial tensile and compressive tests, which were followed by reversal of the loading direction at a prestrain of 1%. The influence of the grain size on the intensity of the Bauschinger effect was investigated. The Bauschinger effect is interpreted to be a manifestation of internal stresses produced near the grain boundaries by the accumulation of dislocations. On the basic of our experimental results, the roles of the grain boundaries, which are usually at least partially considered as barriers to dislocation motion, are reconsidered.

Microstructure and Properties of Ti Rods Produced by Multi-Step SPD

2006 ◽  
Vol 503-504 ◽  
pp. 763-768 ◽  
Author(s):  
V.V. Latysh ◽  
Irina P. Semenova ◽  
G.H. Salimgareeva ◽  
I.V. Kandarov ◽  
Yuntian T. Zhu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Yield Stress ◽  
Equal Channel Angular Pressing ◽  
Thermomechanical Treatment ◽  
Ultrafine Grained Structure ◽  
Annealed State ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Cp Ti

This paper studies the effect of combined SPD treatment on microstructure and mechanical properties of semi-products out of CP Ti. The combined processing, consisting of equal-channel angular pressing and further thermomechanical treatment, produced ultrafine-grained rods out of Grade 2 CP Ti with a diameter of 6.5 mm and a length of up to 1 m. It was established that the formation of homogeneous ultrafine-grained structure in Ti rod with α-grain size of about 100 nm allowed to enhance yield stress by 200% in comparison with initial annealed state.

Nanograin size effects on deformation mechanisms and mechanical properties of nickel: A molecular dynamics study

2021 ◽  
Vol 11 (11) ◽  
pp. 1841-1855
Author(s):  
Alexandre Melhorance Barboza ◽  
Ivan Napoleão Bastos ◽  
Luis César Rodríguez Aliaga
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Stress Relaxation ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Rate Sensitivity ◽  
Deformation Mechanisms ◽  
Triple Junctions ◽  
Grain Sizes

The grain size refinement of metallic materials to the nanometer scale produces interesting properties compared to the coarse-grained counterparts. Their mechanical behavior, however, cannot be explained by the classical deformation mechanisms. Using molecular dynamics simulations, the present work examines the influence of grain size on the deformation mechanisms and mechanical properties of nanocrystalline nickel. Samples with grain sizes from 3.2 to 24.1 nm were created using the Voronoi tessellation method and simulated in tensile and relaxation tests. The yield and ultimate tensile stresses follow an inverse Hall-Petch relationship for grain sizes below ca. 20 nm. For samples within the conventional Hall-Petch regime, no perfect dislocations were observed. Nonetheless, a few extended dislocations were nucleated from triple junctions, suggesting that the suppression of conventional slip mechanism is not uniquely responsible for the inverse Hall-Petch behavior. For samples respecting the inverse Hall-Petch regime, the high number of triple junctions and grain boundaries allowed grain rotation, grain boundary sliding, and diffusion-like behavior that act as competitive deformation mechanisms. For all samples, the atomic configuration analysis showed that Shockley partial dislocations are nucleated at grain boundaries, crossing the grain before being absorbed in opposite grain boundaries, leaving behind stacking faults. Interestingly, the stress relaxation tests showed that the strain rate sensitivity decreases with grain size for a specific grain size range, whereas for grains below approximately 10 nm, the strain rate sensitivity increases as observed experimentally. Repeated stress relaxation tests were also performed to obtain the effective activation volume parameter. However, the expected linear trend in pertinent plots required to obtain this parameter was not found.

Slip traces caused by plastic deformation during recrystallization of thin metal sheets

1994 ◽  
Vol 52 ◽  
pp. 620-621
Author(s):  
H. Lin ◽  
D. P. Pope
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Sample Thickness ◽  
List Type ◽  
Metal Sheets ◽  
Second Phases ◽  
Slip Traces ◽  
Series Of Experiments ◽  
Cold Rolled ◽  
Individual Grains

During a study of mechanical properties of recrystallized B-free Ni3Al single crystals, regularly spaced parallel traces within individual grains were discovered on the surfaces of thin recrystallized sheets, see Fig. 1. They appeared to be slip traces, but since we could not find similar observations in the literature, a series of experiments was performed to identify them. We will refer to them “traces”, because they contain some, if not all, of the properties of slip traces. A variety of techniques, including the Electron Backscattering Pattern (EBSP) method, was used to ascertain the composition, geometry, and crystallography of these traces. The effect of sample thickness on their formation was also investigated.In summary, these traces on the surface of recrystallized Ni3Al have the following properties:1.The chemistry and crystallographic orientation of the traces are the same as the bulk. No oxides or other second phases were observed.2.The traces are not grooves caused by thermal etching at previous locations of grain boundaries.3.The traces form after recrystallization (because the starting Ni3Al is a single crystal).4.For thicknesses between 50 μm and 720 μm, the density of the traces increases as the sample thickness decreases. Only one set of “protrusion-like” traces is visible in a given grain on the thicker samples, but multiple sets of “cliff-like” traces are visible on the thinner ones (See Fig. 1 and Fig. 2).5.They are linear and parallel to the traces of {111} planes on the surface, see Fig. 3.6.Some of the traces terminate within the interior of the grains, and the rest of them either terminate at or are continuous across grain boundaries. The portion of latter increases with decreasing thickness.7.The grain size decreases with decreasing thickness, the decrease is more pronounced when the grain size is comparable with the thickness, Fig. 4.8.Traces also formed during the recrystallization of cold-rolled polycrystalline Cu thin sheets, Fig. 5.

Microstructures and Mechanical Properties of AZ61 Mg Alloy Processed by Equal Channel Angular Pressing

2012 ◽  
Vol 468-471 ◽  
pp. 2124-2127 ◽  
Author(s):  
Shao Feng Zeng ◽  
Kai Huai Yang ◽  
Wen Zhe Chen
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Equal Channel Angular Pressing ◽  
Uniform Elongation ◽  
Considerable Decrease ◽  
Angular Pressing ◽  
Az61 Magnesium Alloy ◽  
Average Grain Size ◽  
Microstructures And Mechanical Properties ◽  
Bimodal Grain Size

Equal channel angular pressing (ECAP) was applied to a commercial AZ61 magnesium alloy for up to 8 passes at temperatures as low as 473K. Microstructures and mechanical properties of as-received and ECAP deformed samples were investigated. The microstructure was initially not uniform with a “bimodal” grain size distribution but became increasingly homogeneous with further ECAP passes and the average grain size was considerably reduced from over 26 μm to below 5 μm. The ultimate tensile strength (UTS) decreases clearly after one pass, but increases significantly up to two passes, and then continuously slowly decreases up to six passes, and again increases slightly up to eight passes. In contrast, the uniform elongation increased significantly up to 3 passes, followed by considerable decrease up to 8 passes. These observations may be attributed to combined effects of grain refinement and texture development.

Investigations on Microstructure Evolution and Deformation Behavior of Aged and Ultrafine Grained Al-Zn-Mg Alloy Subjected to Severe Plastic Deformation

2010 ◽  
Vol 667-669 ◽  
pp. 253-258
Author(s):  
Wei Ping Hu ◽  
Si Yuan Zhang ◽  
Xiao Yu He ◽  
Zhen Yang Liu ◽  
Rolf Berghammer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Plastic Deformation ◽  
Grain Size ◽  
Severe Plastic Deformation ◽  
Microstructure Evolution ◽  
Deformation Behavior ◽  
Deformation Mechanisms ◽  
Mg Alloy ◽  
Ultrafine Grained

An aged Al-5Zn-1.6Mg alloy with fine η' precipitates was grain refined to ~100 nm grain size by severe plastic deformation (SPD). Microstructure evolution during SPD and mechanical behaviour after SPD of the alloy were characterized by electron microscopy and tensile, compression as well as nanoindentation tests. The influence of η' precipitates on microstructure and mechanical properties of ultrafine grained Al-Zn-Mg alloy is discussed with respect to their effect on dislocation configurations and deformation mechanisms during processing of the alloy.

Mechanical properties and corrosion behaviour of ultrafine-grained AA6082 produced by equal-channel angular pressing

2008 ◽  
Vol 43 (23-24) ◽  
pp. 7409-7417 ◽  
Author(s):  
Matthias Hockauf ◽  
Lothar W. Meyer ◽  
Daniela Nickel ◽  
Gert Alisch ◽  
Thomas Lampke ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Equal Channel Angular Pressing ◽  
Corrosion Behaviour ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Mechanical Properties And Corrosion
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