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1

Microstructure and Properties of Cu-Nb Wire Composites

Głuchowski W. J., Rdzawski Z.M., Stobrawa J. P., Marszowski K. J.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 1

35--40

EN

Nowadays, there is much activity all over the world in development of Cu-Nb composites for their potential use as conductors in high field magnets. This study was aimed at investigation of microstructure, mechanical and electrical properties of Cu-Nb composite wires. The investigated materials have been processed by vacuum furnace melting and casting, and then hot forging and cold drawing. Initial results of research into Cu-Nb composite material obtained using repeated iterative drawing of niobium wires compacted into copper tube, have been also presented in this article. The ultimate tensile strength versus cold deformation degree has been presented. These changes have been discussed in relation to microstructure evolution. It was assumed that repeated drawing of compacted wires is a promising method for fibrous composite production (more than 823,000 Nb fibres of nanometric diameter) characterized by high mechanical properties and electrical conductivity. Original SPD technique applied for Cu-Nb composite deformation result in initial microstructure refinement and improves effectiveness of wire production process.

PL

Aktualnie obserwuje się na świecie intensywny rozwój kompozytów Cu-Nb stosowanych jako przewody nawojowe generatorów silnych pól magnetycznych. Badania miały na celu określenie mikrostruktury oraz właściwości mechanicznych i elektrycznych drutów kompozytowych Cu-Nb. Badane materiały wytworzono przez zastosowanie topienia i odlewania w piecu próżniowym, a następnie kucia na gorąco i ciągnienia. Zaprezentowano także wstępne wyniki badań wytwarzania kompozytu Cu-Nb na drodze iteracyjnego ciągnienia pakietu drutów niobowych w rurze miedzianej. Pokazano wyniki badań wytrzymałości na rozciąganie w zależności od stopnia odkształcenia, w powiązaniu ze zmianami mikrostruktury. Stwierdzono, że wielokrotne ciągnienie pakietu drutów jest obiecująca metoda wytwarzania kompozytów włóknistych (ponad 823000 włókien Nb o przekroju nanometrycznym) o wysokich właściwościach mechanicznych i konduktywności elektrycznej.

2

Nanocrystalline copper based microcomposites

Stobrawa J. P., Rdzawski Z.M., Głuchowski W., Domagała-Dubiel J.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 54, nr 1

49--57

EN

Purpose: The aim of this work was to investigate microstructure, mechanical properties and deformation behavior of copper microcomposites: Cu- Y2O3, Cu- ZrO2 and Cu-WC produced by powder metallurgy techniques. Design/methodology/approach: Tests were made with Cu-Y2O3, Cu-ZrO2 and Cu-WC microcomposites containing up to 2% of a strengthening 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, additionally, measurements of HV hardness and electrical conductivity were made. Analysis of the initial nanocrystalline structure of these materials was made and its evolution during sintering and cold deformation was investigated. Findings: It was found out that addition of up to 2 wt.% of a strengthening phase significantly improves mechanical properties of the material and increases its softening point. The obtained strengthening effect have been discussed based on the existing theories related to strengthening of nanocrystalline materials. The studies have shown importance of “flows” existing in the consolidated materials and sintered materials in pores or regions of poor powder particle connection which significantly deteriorate the 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 input powder milling in a planetary ball mill, followed by compacting and sintering. Additional operations of hot extrusion are also often used. There is some danger, however, that during high-temperature processing or application of these materials at elevated or high temperatures this nanometric structure may become unstable. Practical implications: A growing trend to use new copper based microcomposites is observed recently world-wide. Within this group of materials particular attention is put to those with nanometric grain size of a copper matrix, which show higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the knowledge of mechanical properties and the nanostructure stability of Cu-Y2O3, Cu-ZrO2 and Cu-WC microcomposites. A controlled process of milling, compacting, sintering and cold deformation provides possibility to obtain nanocrystalline copper based materials with improved functional properties.

3

Microstructural characterization of high strength high conductivity Cu-Nb microcomposite wires

Głuchowski W., Stobrawa J. P., Rdzawski Z.M., Marszowski K.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 46, nr 1

40--48

EN

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 electrical conductivity over 40 MS/m) correspond to requirements for production of long pulsed 60T magnets. Originality/value: Original SPD technic applied for Cu-Nb microcomposite deformation cause initial microstructure refinement and improves effectiveness of wire production process.

4

Microstructure evolution in CRCS processed strips of CuCr0,6 alloy

Stobrawa J. P., Rdzawski Z. M., Głuchowski W., Malec W.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 38, nr 2

195-202

EN

Purpose: The aim of this work was to evaluate the ability of a continuous repetitive corrugation and straightening (CRCS) technique in creating ultra fine grained copper-chromium strips as well as to determine the microstructure evolution and its influence on grain size refinement. Design/methodology/approach: Tests were performed with the 0.8 mm thick CuCr0,6 strips using original die set construction. The changes of mechanical properties as well as microstructure evolution versus circles number of deformation were investigated. The microstructure was investigated using optical and electron microscopy (TEM and SEM equipped with EBSD). Findings: The CRCS process effectively reduced the grain size of a CuCr0,6 alloy strips, demonstrating the CRCS as a promising new method for producing ultra fine grained metallic strips. Generally, the mechanism of grain refinement and microstructural evolution during CRCS of CuCr0,6 alloy strips is similar to that observed in other high/medium stacking fault energy materials deformed by SPD, i.e. via dislocation manipulation and accumulation. Any effects connected with mechanical twinning were not observable. Research limitations/implications: Investigation results are limited to the initial material in annealed state. Further investigation should focus on the description of influence of deformation-supersaturation-ageing sequence on strengthening effect. Practical implications: A growing trend to use new copper-based functional materials is recently observed world-wide. Within this group of materials particular attention is drawn to those with ultra fine or nanometric grain size of a copper matrix, which show higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the mechanical properties of precipitates strengthened ultra fine grained copper - chromium alloy strips obtained by original RCS method and to the microstructure evolution.

5

Microstructure evolution in CRCS processed strips of CuCr0,6 alloy

Stobrawa J.P., Rdzawski Z.M., Głuchowski W., Malec W.

Archives of Computational Materials Science and Surface Engineering

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2010

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Vol. 2, nr 3

125-132

EN

Purpose: The aim of this work was to evaluate the ability of a continuous repetitive corrugation and straightening (CRCS) technique in creating ultra fine grained copper-chromium strips as well as to determine the microstructure evolution and its influence on grain size refinement. Design/methodology/approach: Tests were performed with the 0.8 mm thick CuCr0,6 strips using original die set construction. The changes of mechanical properties as well as microstructure evolution versus circles number of deformation were investigated. The microstructure was investigated using optical and electron microscopy (TEM and SEM equipped with EBSD). Findings: The CRCS process effectively reduced the grain size of a CuCr0,6 alloy strips, demonstrating the CRCS as a promising new method for producing ultra fine grained metallic strips. Generally, the mechanism of grain refinement and microstructural evolution during CRCS of CuCr0,6 alloy strips is similar to that observed in other high/medium stacking fault energy materials deformed by SPD, i.e. via dislocation manipulation and accumulation. Any effects connected with mechanical twinning were not observable. Research limitations/implications: Investigation results are limited to the initial material in annealed state. Further investigation should focus on the description of influence of deformation-supersaturation-ageing sequence on strengthening effect. Practical implications: A growing trend to use new copper-based functional materials is recently observed world-wide. Within this group of materials particular attention is drawn to those with ultra fine or nanometric grain size of a copper matrix, which show higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the mechanical properties of precipitates strengthened ultra fine grained copper -chromium alloy strips obtained by original RCS method and to the microstructure evolution.

6

Ultrafine grained strips of CuCr0.6 alloy prepared by CRCS method

Stobrawa J. P., Rdzawski Z. M., Głuchowski W., Malec W.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 33, nr 2

166-172

EN

Purpose: The aim of this work was to evaluate the ability of a continuous repetitive corrugation and straightening (CRCS) technique in creating ultra fine grained copper-chromium strips as well as to determine their deformability, mechanical properties, deformation behaviour and microstructure evolution. Design/methodology/approach: Tests were performed with the 0.8 mm thick CuCr0.6 strips using original die set construction. The changes of mechanical properties as well as microstructure evolution versus number of deformation cycles were investigated. The microstructure was investigated using optical and electron microscopy (TEM and SEM equipped with EBSD). Findings: The obtained strengthening effects and observed microstructure changes have been discussed basing on the existing theories related to strengthening of ultra fine grained copper based materials. The CRCS process effectively reduced the grain size of a CuCr0.6 alloy strips, demonstrating the CRCS as a promising new method for producing ultra fine grained metallic strips. Research limitations/implications: Research results are limited to the initial material after annealing only. Further investigations should be aimed towards determination of CRCS sequence including deformation-precipitation-ageing influence on strengthening effect. 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 ultra fine or nanometric grain size of a copper matrix, which exhibit higher mechanical properties than microcrystalline copper. Originality/value: The paper describes to the mechanical properties of precipitates strengthened ultra fine grained copper - chromium alloy strips obtained by original RCS method and to the microstructure evolution.

7

Structure and properties of CuFe2 alloy

Rdzawski Z. M., Stobrawa J. P., Głuchowski W.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 33, nr 1

7-18

EN

Purpose: The objective of this work was to investigate the changes taking place in the structure and properties of CuFe2 alloy caused by combined heat treatment and metal working. The objective of this paper was to describe phenomena related to the formation of functional properties CuFe2 strips, especially for obtaining hardness in 120-140 HV range and electrical conductivity above 35 MS/m. Design/methodology/approach: The investigated material consisted of two industrial melts of CuFe2. Systematic investigations of selected variants of heat treatment and plastic working operations were carried out. The investigations started with description of microstructure and properties in initial state, after quenching, after cold working, quenching and ageing, after quenching and ageing, after quenching, ageing and cold working and after cold working and annealing - omitting quenching and ageing process. Hardness test (HV) and electrical conductivity were determined on strip samples. Typical tension tests and metallographic investigations were also carried out. Findings: Structure and properties of industrial CuFe2 alloy differs significantly from the literature descriptions, especially after quenching process. It could be assumed, that the dissolved in a melting process alloy additives (in this case a part of dissolved iron) might be supersaturated, but some of them might be precipitated. This theory was confirmed by the results of investigation into mechanical properties, microstructure and electrical conductivity. Practical implications: The presented investigation results, besides their cognitive values, provide many useful information which might be implemented in a industrial practice. Originality/value: It was assumed that cold deformation with rolling reduction 70% and annealing at temperature 480oC for 12 hours provided possibilities to reach maximal electrical conductivity 37 MS/m and maximal hardness 136 HV.

8

Characterisation of nanostructured copper - WC materials

Stobrawa J. P., Rdzawski Z. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 32, nr 2

171-178

EN

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.

9

Structure and properties of dispersion hardened submicron grained copper

Stobrawa J. P., Rdzawski Z. M., Głuchowski W.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

195-198

EN

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 copper-based 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 degrees centigrade, gives possiblity 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 microcomposites 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 submikron size, gives possibility for significant improvements in functional properties of the materials.

10

Microstructure stability of the PtRh alloys used for catalytic ammonia oxidation

Rdzawski Z. M., Stobrawa J. P., Szynowski J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

106-114

EN

Purpose: The aim of this work was to investigate the possibility of increasing performance of the PtRh alloys used in industrial processes of catalytic ammonia oxidation. Design/methodology/approach: In order to reach this objective, the extensive studies have been carried out, which were aimed at better understanding of the phenomena taking place on a surface and inside the wires of catalytic gauzes during the process. The electron microscopy methods (SEM, TEM, HRTEM), optical microscopy and microanalysis were used to examine the alloys under investigation. Findings: It was found that the performance and lifetime of the catalytic gauzes is closely related with structural stability of the alloys and with the stability of parameters of the ammonia oxidation process. Practical implications: The PtRh1O-based alloys modified with boron and yttrium have been developed, which are characterised by more stable structure than the classical PtRh1O alloy and enable significant reduction of the grain growth effect during the use of the gauzes. This should contribute to the improvement of the process efficiency and selectivity, and increase the lifetime of the catalytic gauzes. Originality/value: The developed alloys are new and original.

11

Microstructure and properties of nanocrystalline copper - yttria microcomposites

Stobrawa J. P., Rdzawski Z. M., Głuchowski W. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 2

83-86

EN

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 microcomposites 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.

12

Dispersion - strengthened nanocrystalline copper

Stobrawa J. P., Rdzawski Z. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 2

35-42

EN

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 high-temperature 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 world-wide. 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.

13

Precipitation process of the Ni3Al phase in copper-based alloys

Stobrawa J. P., Rdzawski Z. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 15, nr 1-2

21--26

EN

Purpose: This research was aimed to investigate the mechanism of Ni3Al phase precipitation during long-term process of ageing Cu-Ni-Al type alloys with particular account of the precipitates morphology changes, including the changes in their size with varying temperature and ageing time, so as to determine an effect of the elastic strain energy on these changes. Design/methodology/approach: Samples of cold-rolled strips from the CuNi16Al5 alloy were solution – treated at 900°C for 1h in argon atmosphere, water quenched and next aged at the temperatures of 450 and 550°C for up to 380 and 760 hours, respectively. Their microstructure was investigated by transmission electron microscopy. Findings: It was found that decomposition of supersaturated solid solution proceeds by nucleation and growth of the coherent precipitates of the L12 – Ni3Al phase. Their morphology changes as a result of competitive influence of an elastic strain energy, surface energy on the matrix-precipitate inter-phase boundary, and the energy of elastic interaction between precipitates. The L12 – Ni3Al precipitates nucleate as the spherical ones and grow, forming intermediate sub-structures, until they reach a cubic form with the planes parallel to the {100} planes of a matrix and take privileged positions along the <110> directions. Clear deviations from the LSW coagulation theory and its modifications, demonstrated by the slow-down of the process, have been observed. In the extreme case, growth of the precipitates can be completely stopped in some time ranges of the ageing process. Research limitations/implications: Further research should be concentrated on the precipitation kinetics within a wider range of volumetric fraction of the Ni3Al phase in a copper matrix. Practical implications: This effect can be used in practice to stabilise mechanical properties at elevated temperature. Originality/value: The paper contributes to better understanding of the precipitation mechanism in the alloys examined.

14

Deformation behaviour of dispersion hardened nanocrystalline copper

Stobrawa J. P., Rdzawski Z. M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

153--156

EN

Purpose: The aim of this work was to describe deformation behaviour of nanocrystalline copper dispersion-hardened with nanoparticles of tungsten carbide and yttria. Design/methodology/approach: Tests were made with the Cu, Cu-WC and Cu-Y2O3 micro-composites containing up to 3 % of a hardening phase. These were obtained by powder metallurgy techniques, i.e. milling the input powders in the planetary ball mills, compacting and sintering. The mechanical properties (hardness, 0,2 YS, elongation during compression test) and microstructure were examined by the optical, scanning and transmission electron microscopy. 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 hardening effect and the changes in the mechanical and plastic properties. Results of this analysis have been discussed based on the existing theories related to hardening of nanocrystalline materials. 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 high-temperature processing or using these materials at elevated or high temperatures this nanometric structure may become unstable. The studies have shown the importance of “flows” in the consolidated materials such as pores or regions of poor powder particles joining which significantly deteriorate mechanical properties of compacted and sintered powder micro composites. 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 of a copper matrix, which exhibit higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the elucidation of deformation behaviour of high-porosity nanocrystalline copper dispersion hardened with tungsten carbide and yttria.