The effect of fabrication mode on microstructure, texture and strength in cu-nb/ti composite (original) (raw)
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Materials Research, 2001
Cu-Nb microcomposites are attractive in magnet pulsed field technology applications due to their anomalous mechanism of mechanical strength and high electrical conductivity. In this sense, recently it was conceived the use of Cu 15% vol. Nb wires to operate as a high tensile strength cable for a diamond cutting tool (diamond wires) for marble and granite slabbing. The multifilamentary Cu 15% vol. Nb composite was obtained using a new processing route, starting with niobium bars bundled into copper tubes, without arc melting. Cold working techniques, such as swaging and wire drawing, combined with heat treatments such as sintering and annealing, and tube restacking were employed. The tensile property of the composite was measured as a function of the niobium filaments dimensions and morphology into the copper matrix, in the several processing steps. An ultimate tensile strength (UTS) of 960 MPa was obtained for an areal reduction (R = Ao/A, with Ao-initial cross section area, and A-final cross section area) of 4x10 8 X, in which the niobium filaments reached thickness less than 20 nm. The anomalous mechanical strength increase is attributed to the fact that the niobium filaments acts as a barrier to copper dislocations. Figure 6. Stress versus strain curve for the Cu 15 vol.% Nb composite.
Microstructural characterization of high strength high conductivity Cu-Nb microcomposite wires
Purpose: The properties and the microstructure of cold drown Cu-Nb composites have been investigated for their potential use as conductors in high field magnets. Nowadays, there is much activity in the development of such conductors all over the world. Design/methodology/approach: This study was aimed to investigate microstructure, mechanical and electrical properties of Cu-Nb15 wires. The investigated materials have been processed by vacuum furnace melting and casting, further hot forging and cold drawing. Alternatively material has been processed by one of the SPD (severe plastic deformation) method using oscillatory turning die pressing. Microstructure has been observed by optical and electron microscopy technics. Findings: The ultimate tensile strength versus cold deformation degree have been presented. These changes have been discussed in relation to the microstructure evolution. Practical implications: The obtained mechanical and electrical properties (UTS over 900 MPa and ele...
Problems in evaluating the dislocation densities in heavily deformed Cu-Nb composites
Ultramicroscopy, 1989
The dislocation density of the Cu matrix in a heavily cold-rolled Cu-20%Nb composite is evaluated as a function of deformation strain. The methods and problems involved in this analysis are described and discussed in detail. The maximum dislocation density was found to be 101°-10 u cm-z at all strains investigated. Dislocations were not uniformly distributed but rather had a low energy dislocation structure. The effects of sample preparation, specifically ion-thinning, were evaluated and found to have little effect on the dislocation population of worked Cu but actually introduced defects into annealed Cu.
MRS BULLETIN • VOLUME 35 • DECEMBER 2010
We review microstructures and properties of metal matrix composites produced by severe plastic deformation of multiphase alloys. Typical processings are wire drawing, ball milling, roll bonding, equal-channel angular extrusion, and high-pressure torsion of multiphase materials. Similar phenomena occur between solids in frictional contact such as in tribology, friction stir welding, and explosive joining. The resulting compounds are characterized by very high interface and dislocation density, chemical mixing, and atomic-scale structural transitions at heterointerfaces. Upon straining, the phases form into nanoscaled fi laments. This leads to enormous strengthening combined with good ductility, as in damascene steels or pearlitic wires, which are among the strongest nanostructured bulk materials available today (tensile strength above 6 GPa). Similar materials are Cu-Nb and Cu-Ag composites, which also have good electrical conductivity that qualifi es them for use in high-fi eld magnets. Beyond the engineering opportunities, there are also exciting fundamental questions. They relate to the nature of the complex dislocation, amorphization, and mechanical alloying mechanisms upon straining and their relationship to the enormous strength. Studying these mechanisms is enabled by mature atomic-scale characterization and simulation methods. A better understanding of the extreme strength in these materials also provides insight into modern alloy design based on complex solid solution phenomena.
Plasticity Mechanisms in Multi-Scale Copper-Based Nanocomposite Wires
Materials Science Forum, 2007
Copper-based high strength nanofilamentary wires reinforced by Nb nanofilaments are prepared by severe plastic deformation (repeated hot extrusion, cold drawing and bundling steps) for the winding of high pulsed magnets. The effects of microstructure refinement on the plasticity mechanisms were studied via nanoindentation, in-situ deformation in TEM and under neutron beam: all results evidence size effects in each nanostructured phase of the nanocomposite wires, i.e. single dislocation regime in the finest regions of the Cu matrix and whisker-like behaviour in the Nb nanofilaments. The macroscopic high yield stress is thus the results of the combination of the different elastic-plastic regimes of each phase that include size effects.
Microstructure and strength of severely deformed fcc metals
Materials Science and Engineering: A, 2007
The relationship is examined between the microstructure and the strength of ultrafine-grained fcc metals (Al, Al-Mg alloys, Cu and Ni) processed by severe plastic deformation. The saturation value of the yield strength obtained at high strains is correlated with the dislocation density by using the Taylor equation. The results suggest that the main strengthening mechanism in severely deformed fcc metals is the interaction between dislocations. Furthermore, the saturation strength of different fcc metals deformed at room temperature may be described by using the shear modulus and the absolute melting point. The results of the analysis show that for Al-Mg alloys the addition of the Mg alloying element to the Al matrix leads to an increase in the maximum value of the dislocation density and consequently to an increase in the strength.
Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. In this article, a dislocation- density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with the experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule- of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.
Size effect on the tensile strength of fine-grained copper
Scripta Materialia, 2008
We considered the effect of the thickness of copper sheet on its tensile strength. A model in which the strength of surface grains is governed by dislocation image forces, while that of interior grains is determined by dislocation cell structure, was proposed. Using a rule of mixtures, the dependence of strength on the specimen thickness was calculated. A master curve representing the calculated dependence of normalized strength on the ratio of sheet thickness to grain size was confirmed by experiment.
Materials Science Forum, 2006
A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals.
Mechanics of Materials, 2011
In this work a dislocation based constitutive description for modeling the thermo visco plastic behavior of FCC metals has been developed. The constitutive description, which is founded on the concepts of thermal activation analysis and dislocation dynamics, assumes the plastic flow additively decomposed into internal stress and effective stress. The internal stress represents the applied stress required for the transmission of plastic flow between the polycrystal grains and it is defined by the Hall Petch relationship. The effective stress formulation, which is the main innovative feature of this work, represents the thermally activated deformation behavior. This is defined taking into account the interrelationship between strain rate and temperature, and gathers structural evolution dependence. This structural evolution is described as a function of dislocations density, which acts as internal state variable in the material deformation behavior. A systematic procedure for identifica tion of the material parameters is developed and the model is applied to define the behav ior of annealed OFHC copper. The analytical predictions of the constitutive description are compared with the experimental data reported by Nemat Nasser and Li (Nemat Nasser, S., Li, Y., (1998). Flow stress of FCC polycrystals with application to OFHC Copper. Acta Mater. 46, 565 577). Good correlation between experiments and analytical predictions is found within wide ranges of strain rate and temperature.