Wyniki wyszukiwania - Biblioteka Nauki

1

Precipitation process of the Ni3Al phase in copper-based alloys

100%

Stobrawa J. P. , Rdzawski Z. M.

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2006

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tom 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.

2

Characterisation of nanostructured copper - WC materials

100%

Stobrawa J. P. , Rdzawski Z. M.

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tom 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.

3

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

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

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tom 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.

4

Structure and properties of CuFe2 alloy

80%

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

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tom 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.

5

Microstructure and Properties of Cu-Nb Wire Composites

80%

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

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tom 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.