Papers by Keyword: Nanostructured Copper

Abstract: Measurements of the elasticity modulus and Poisson’s ratio on nanostructured iron obtained by mechanical milling and on nanostructured copper obtained by severe plastic deformation (ECAP) have been carried out. Iron powder was severely deformed in a planetary ball milling. Powder compaction was done in a testing machine, obtaining cylinders that were compacted at temperatures between 425°C and 500°C. Commercial Cu of 99.98 wt % purity was processed at room temperature by Equal-Channel Angular Pressing (ECAP) following the route Bc. Heavy deformation was introduced in the samples after a considerable number of ECAP passes, from 1 to 16. A significant grain refinement was observed after processing the samples. The most important microstructural and mechanical changes were introduced in the first ECAP pass. Elasticity modulus and Poisson’s ratio were determined in iron and copper samples by ultrasonic measurement using an ultrasonic pulser-receiver and two transducers appropriate to the tested materials for pulse-echo sound velocity measurement in longitudinal and shear modes.

Abstract: This paper reviews our recent studies on the effect of twin boundary (TB) on the deformation behavior in Cu with nanoscale growth twins. In situ straining transmission electron microscopy investigations on TB migration, TBs and twin ends acting as dislocation emission sources, and the interactions between dislocations and TBs are highlighted. Results provide some useful understanding of why Cu with nanoscale twins leads to a combination of ultrahigh strength and high ductility.

Abstract: Copper has widespread use as engineering material, because of its structural and functional properties, notably high thermal and electrical conductivity. A major drawback of this base metal and its alloys is a relatively low hardness. This precludes its utilization in applications in which both high conductivity and high strength/hardness are needed, e.g. in injection moulds for plastics. Nanostructured metals and nanocomposites are ways to address the low hardness problem, provided the nanostructured material is thermally stable during processing and service. In the present research, composite powders, with 5 to 30 at % nanodiamond, were consolidated into bulk samples. The copper-nanodiamond composite powders were vacuum encapsulated and extruded at 600°C. A significant proportion of the initial hardness in the powders is retained after extrusion. Transmission electron microscopy (TEM) of the extruded material indicates good bonding between the nanodiamond particles and the copper matrix. Raman spectroscopy on the consolidated samples evidences the presence of graphite, possibly due to partial disintegration of ultradisperse nanodiamond agglomerates.

Abstract: Copper nitride films prepared by sputtering have applications such as optical data storage material, insulation barriers in micro electronic devices and coatings for mechanical applications. The present study examines nanocomposites prepared by mechanical alloying of copper with copper nitride under nitrogen atmosphere, at room temperature, in order to establish a comparison with properties of Cu-N sputtered films. The powders were consolidated into bulk samples via warm extrusion at temperatures ranging from 300 to 500°C (0.42-0.64 Tf) after encapsulation without degassing. The as-milled powders and the extruded materials were studied using X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and microhardness measurements. Also, the TEM observation of the extruded sample indicates a mean grain size of about 50 nm. This evidences a higher thermal stability of the as-milled powders and the advantage of using a fast consolidation process, at a relatively low temperature. Therefore, the consolidated material did not show the dramatic softening associated with recrystallization. The consolidation of nanostructured copper-copper nitride composite powders via warm extrusion, without major grain coarsening, was demonstrated.

Abstract: Accumulative roll-bonding (ARB) process was applied to an oxygen free copper for improvement of the mechanical properties via ultra grain refinement to nanometer order level. Two copper sheets 1mm thick, 30mm wide and 300mm long are degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and cold-roll-bonded by 50% reduction rolling. The sheet is then cut to the two pieces of same length and the same procedure was repeated to the sheets. The ARB process up to eight cycles (an equivalent thickness strain of 6.4) is successfully performed at ambient temperature. TEM observation reveals that ultrafine grains, hardly containing the dislocation interior, begin to develop at the third cycle, and after the sixth cycle they cover most of regions of samples. The morphology of ultrafine grains formed is different from that of aluminum alloys. Tensile strength of the ARB-processed copper increases with the equivalent strain up to a strain of ~3.2, in which it reached 390 MPa, ~2.1 times higher than the initial value. However, the strength hardly changed at the strain above ~3.2.