Deformation behaviour of dispersion hardened nanocrystalline copper (original) (raw)
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Dispersion–strengthened nanocrystalline copper
2007
Purpose: The aim of this work was to investigate microstructure, mechanical properties and deformation behaviour of dispersion strengthened nanocrystalline copper produced by powder metallurgy techniques. Design/methodology/approach: Tests were performed with the Cu, Cu-tungsten carbide and Cu-yttria micro-composites containing up to 3 wt.% of a strengthening particles. The mechanical properties, initial nanocrystalline structures and their evolution during deformation processes were investigated. Findings: The obtained strengthening effect have been discussed based on the existing theories related to strengthening of nanocrystalline materials. The studies have shown the importance of "flows" existing in the consolidated materials and sintered materials such as pores or regions of poor powder particle joining which significantly deteriorate mechanical properties of micro-composites produced by powder metallurgy. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copper-based bulk materials by means of milling input powders in the planetary ball, followed by compacting and sintering. Additional operations of hot extrusion are also often used. There is some threat, however, that during hightemperature processing or using these materials at elevated or high temperatures this nanometric structure may become unstable. Practical implications: A growing trend to use new copper-based functional materials is observed recently worldwide. Within this group of materials particular attention is drawn to those with nanometric grain size of a copper matrix, which exhibit higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the mechanical properties of dispersion strengthened (with tungsten carbide and yttria) nanocrystalline copper and to the elucidation of deformation behaviour of these materials with high porosity.
Characterisation of nanostructured copper - WC materials
2009
AbstrAct Purpose: The aim of this work was to determine the microstructure and properties stability of nanocrystalline copper dispersion hardened with nanoparticles of tungsten carbides. Design/methodology/approach: Tests were made with Cu and Cu -WC micro -composites containing up to 3% of a hardening phase. The materials were fabricated by powder metallurgy techniques, including milling of powders, followed by their compacting and sintering. The main mechanical properties of the materials were determined from the compression test, and, moreover, measurements of the HV hardness and electrical conductivity have been made. Analysis of the initial nanocrystalline structure of these materials was made and its evolution during sintering was investigated. Findings: It was found that an addition of up to 1.5 wt % of a WC significantly improves mechanical properties of the material and increases its softening point. Research limitations/implications: The powder metallurgy techniques make it possible to obtain nanocrystalline copper-based bulk materials. Additional operations of hot extrusion are also often used. There is some threat, however, that during high temperature processing or application these materials this nanometric structure may become unstable. Practical implications: A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to those with nanometric grain size. Originality/value: The paper contributes to the determination of WC nanoparticles content on the mechanical properties and the nanostructure stability of Cu-WC micro-composites.
Structure and properties of dispersion hardened submicron grained copper
AbstrAct Purpose: The objective of the work was to investigate changes in structure and properties of Cu -WC microcomposites which take place in the process of controlled hot deformation of materials of nanometric initial structure. Design/methodology/approach: Tests were made with the Cu-WC micro-composites containing up to 2% of a hardening phase. These were obtained by powder metallurgy techniques and further hot deformation. The mechanical properties and microstructure (by the optical, scanning and transmission electron microscopy) were examined. Findings: Analysis of the initial nanocrystalline structure of these materials was made, and its evolution during hot deformation process was investigated with an account of the changes in the mechanical and electrical properties. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copperbased bulk materials. Globular structure and high porosity of this materials result in their limited mechanical properties. This is the reason why additional operations, should be applied. The investigations have revealed that controlled hot deformation, within the temperature range of 500 -550°C, gives possibility for obtaining submicron grain size and more advantageous mechanical properties of Cu-WC microcomposites. Practical implications: A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to dispersion hardened microcomposities with nanometric or submicron grain size of a copper matrix, which exhibit higher mechanical properties. Originality/value: The paper shows instability of nanostructure of Cu-WC microcomposites in the processes of hot deformation. A controlled process, which can lead to destruction of globular structure, significant improvement of density and obtaining of submicron size, gives possibility for significant improvements in functional properties of the materials.
Microstructural evolution and mechanical properties of nanostructured copper
Proceedings of the Estonian Academy of Sciences. Engineering, 2005
Nanostructured metallic materials exhibit outstanding mechanical properties. Pure copper was chosen as a test material and was subjected to an equal channel angular pressing to produce a nanostructure. The paper analyses development of the microstructure during severe plastic deformation of copper and mechanical properties of the metal. Tests show that the nanocristalline copper possesses high tensile strength and microhardness as well as high plasticity after hard cyclic viscoplastic deformation. However, heat treatment and method of deformation influence the properties to a large extent. Dependence of the changes in structural parameters and properties on the deformation process and heat treatment are studied.
Microstructure and properties of nanocrystalline copper - yttria
AbstrAct Purpose: The objective of the work was to investigate changes in structure and properties of Cu -yttria microcomposites which take place in the process of controlled sintering and deformation of materials of nanometric initial structure. Design/methodology/approach: Tests were made with the Cu-yttria micro-composites containing up to 3 % of a hardening phase. These were obtained by powder metallurgy techniques and further deformation. The mechanical properties and microstructure (by the optical, scanning and transmission electron microscopy) were examined. Findings: Analysis of the initial nanocrystalline structure of these materials was made, and its evolution during deformation process was investigated with an account of the changes in the mechanical and electrical properties. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copper-based bulk materials. Globular structure, high porosity and low sintering temperature of this materials result in their limited mechanical properties. Practical implications: A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to dispersion hardened microcomposities with nanometric or submicron grain size of a copper matrix, which exhibit higher mechanical properties. Originality/value: A controlled process of milling compacting, sintering and cold deformation, allow to obtain nanocrystalline copper based materials with improved functional properties.
Mechanical properties of nanocrystalline copper and nickel
Materials Science and Technology, 2004
The present review paper traces the development of nanocrystalline copper (Nc-Cu) and nanocrystalline nickel (Nc-Ni) and their mechanical properties. The objective is to summarise the various results available in the literature. The mechanical properties discussed are elastic modulus, Poisson's ratio, hardness, yield stress, ultimate tensile stress, strain/elongation to failure, superplasticity, creep, fatigue and fracture properties. The review is limited to bulk nanocrystalline materials. Shortcomings and limitations of the various studies that have been conducted are also highlighted. The present compilation is expected to be useful for researchers engaged in experimental work and computer modelling in this area.
Materials & Design, 2011
Elemental powders of copper (Cu), tungsten (W) and graphite (C) were mechanically alloyed in a planetary ball mill with different milling durations (0-60 h), compacted and sintered in order to precipitate hard tungsten carbide particles into a copper matrix. Both powder and sintered composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and assessed for hardness and electrical conductivity to investigate the effects of milling time on formation of nanostructured Cu-WC composite and its properties. No carbide peak was detected in the powder mixtures after milling. Carbide WC and W 2 C phases were precipitated only in the sintered composite. The formation of WC began with longer milling times, after W 2 C formation. Prolonged milling time decreased the crystallite size as well as the internal strain of Cu. Hardness of the composite was enhanced but electrical conductivity reduced with increasing milling time.
Mechanical behavior of nanocrystalline copper
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
The mechanical behavior of nanocrystalline materials has been studied extensively for the past few years. Recent studies on artifact-free materials with nanosize grains less than 100 nm have been very fruitful. These nanograined metals have exhibited very high strengths with reasonably good ductility. While there have been a large number of studies on hardness and strength characteristics, studies on strain rate sensitivity (SRS) are very limited. We describe here some of our recent work in characterizing SRS as well as activation volumes of nanograined copper using different testing procedures. These tests have been carried out under iso-strain rate and iso-structural conditions.
Elastic and tensile behavior of nanocrystalline copper and palladium
Acta Materialia, 1997
The elastic and tensile behavior of high-density, high-purity nanocrystalline Cu and Pd was determined. Samples with grain sizes of 10-l 10 nm and densities of greater than 98% of theoretical were produced by inert-gas condensation and warm compaction. Small decrements from coarse-grained values observed in the Young's modulus are caused primarily by the slight amount of porosity in the samples. The yield strength of nanocrystalline Cu and Pd was 10-15 times that of the annealed, coarse-grained metal. Total elongations of 14% were observed in samples with grain sizes less than 50 nm, while a sample with a grain size of 110 nm exhibited > 8% elongation, perhaps signifying a change in deformation mechanism with grain size. Hardness measurements followed the predictions of the Hall-Petch relationship for the coarse-grained copper down to x 15 nm, and then plateaued. Hardness values (divided by 3) were 2-3 times greater than the tensile yield strengths. Processing flaws may cause premature tensile failure and lower yield strengths. The size and distribution of processing flaws was determined by small-angle neutron scattering. Tensile strength increased with decreasing porosity, and may be significantly affected by a few large processing flaws. VI 1997 Acta Metallurgica Inc.
Microstructure and properties development of copper during severe plastic deformation
Materials & Design, 2007
Annealed pure copper was subjected to equal-channel angular pressing (ECAP) to produce a nanocrystalline (NC) structure. The microstructure and the development of the mechanical properties of copper under severe plastic deformation (SPD) were studied. The structural changes and the properties due to heat treatment and the different loading methods of NC copper were analyzed and compared. The results show that the heat treatment and the hard cyclic deformation in the viscoplastic regime influence the properties of NC copper to a great extent. The ultimate tensile strength and the microhardness of NC copper decrease while heat-treated NC copper acquires enhanced true tensile properties after hard cyclic deformation in the viscoplastic regime.