Warm compaction powder metallurgy of Cu

A series of experiments were carried out using different admixed lubricant contents, different compaction pressures and temperatures in order to study the warm compaction of copper powder. Results show that too much admixed lubricant will lead to the squeeze out of the lubricant from the compact during the warm compaction processing of Cu powder. Results also show that blisters can be found in sintered samples that contain lubricant less than 0.15%(mass fraction). Optimal warm compaction parameters for producing high density powder metallurgy copper material are obtained. Compacts with green density of 8.6 g/cm^3 and a sintered density of 8.83 g/cm3 can be produced by warm compacting the Cu powder, which contains 0.2% admixed lubricant, and is compacted at 145℃ with a pressure of 700 MPa.     

Structure of vacuum Cu–Ta condensates

The structure of vacuum condensate foils (separated from substrates) of the binary Cu–Ta system has been investigated both in the initial condensed state and after annealings at temperatures of up to 1000°С. It has been shown that the alloying of a vapor flow of the matrix metal (copper) with tantalum to ~0.5 at % makes it possible to reduce the grain size from 3 μm to 50 nm. Depending on the tantalum concentration, condensates exhibit a broad spectrum of structural states, i.e., single- and two-phase, a supersaturated solution of tantalum in the fcc lattice of copper, etc. The structure of the objects possesses a high thermal stability. The temperature of the start of grain growth in the copper matrix depends on the tantalum content and can reach 900°С. The dispersion of the structure of copper condensates and its thermal stability is due to the formation of segregates of tantalum atoms at the boundaries of grains of the copper matrix both in the process of condensation and upon subsequent annealing.     

Influence of Al addition on microstructures of Cu−B alloys and Cu−ZrB2 composites

The influence of Al addition on the microstructure of Cu−B alloys and Cu−ZrB₂ composites was investigated using scanning electron microscopy, X-ray diffraction and first-principles calculation. The results show that the eutectic B in Cu−B alloys can be modified by Al from coarse needles to fine fibrous structure and primary B will form in hypoeutectic Cu−B alloys. As for Cu−ZrB₂ composites, Al can significantly refine and modify the morphology of ZrB₂ as well as improve its distribution, which should be due to its selective adsorption on ZrB₂ surfaces. The first-principles calculation results indicate that Al is preferentially adsobed on ZrB₂ (12(__)10), then on ZrB₂ (101(__)0), and finally on ZrB₂ (0001). As a result, smaller sized ZrB₂ with a polyhedron-like, even nearly sphere-like morphology, can form. Due to Al addition, the hardness of Cu−ZrB₂ composites is greatly enhanced, but the electrical conductivity of the composites is seriously reduced.     

Effect of Cu element on morphology of TiB2 particles in TiB2/Al−Cu composites

In order to explore the influence of Cu element on the morphology evolution of the in-situ TiB₂ particles, the 10 wt.% TiB₂ reinforced Al−5wt.%Cu based composite was prepared by mixed salt casting. The morphology characterization and transformation of TiB₂ reinforcements caused by Cu element were investigated by multi-scale microstructure characterization and statistics techniques. In the case of controlled casting, 5 wt.% Cu addition was found to transform the TiB₂ particle morphology from hexagonal plate with sharp edges and corners to hexagonal or tetragonal prism with chamfered edges and corners with the distinguishing growth steps both on the top surface and the side surface. The TiB₂ growth in Al−Cu matrix followed the rules: nano-scaled spherical nuclei—polyhedron grains—chamfered hexagonal particles—hexagonal plates—chamfered particles with obvious growth steps. The adsorption energy of Cu on different crystal surfaces of TiB₂ was caculated to reveal the influence mechanism and the results indicated that Cu was preferentially adsorbed on the (101(—)1)_TiB2 crystal planes, devoting to the small aspect ratio of TiB₂.     

Research of quasi-solid fracture behavior of casting AI-4.5Cu alloys

1. Introduction Casting Al-Cu alloy with high strength is widely used for its excellent properties in common temperature and high temperature applications. However, this family of alloys has a very special solidification behavior, i.e. wider solidification range, which will result in an inferior cast- ing performance and severe tendency to hot cracking. Hot crack[1] is a very dangerous solidification defect in casting and welding processes. But, up to day, the research on hot cracking is stil…     

Solidification velocity of undercooled Ni–Cu alloys

The solidification velocity of Ni–Cu alloys was measured as a function of bulk undercooling using high-speed thermal imaging of electromagnetically levitated samples. Two departures from power law growth (approximating plateaus) in the velocity versus undercooling data were observed: the first occurred at intermediate undercoolings and is attributed to copper solute, while the second occurred at high undercoolings and is hypothesized to be an effect of oxygen. The Ivantsov solution with marginal stability arguments (IMS model) is a widely used model that relates dendrite growth velocity to total undercooling for dilute alloy systems. However, the model does not predict a plateau at intermediate undercoolings for alloys with a large equilibrium partition coefficient, k_E. Satisfactory agreement between the model and experimental results can be obtained by using a value of k_E that is smaller than the alloy’s actual value, but this is physically unreasonable and causes disagreement with currently accepted kinetic models.     

Comparison of the corrosion resistance of an Al–Cu alloy and an Al–Cu–Li alloy

ABSTRACT

In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005?mol?L^?1 NaCl solution. The severe type of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.     

Electroless deposition of Cu on multiwalled carbon nanotubes

Copper has been deposited on the surface of multiwailed carbon nanombes （MWNTs） and inside MWNTs by electroless deposition. The as-prepared Cu-MWNT composite materials have been characterized by X-ray diffractometer （XRD）, transmission electron microscopy （TEM）, and electrochemical measurement. XRD analyses showed that Cu was a face-centered cubic （fcc） structure. The average size of Cu was calculated by Scherrer＇s formula from XRD data, and it was 11 nm. TEM revealed that Cu grains on the surface of MWNTs were uniform with the sizes of about 30-60 nm. The electrochemical measurement indicated that Cu-MWNT composite materials possessed fine electron conductivity.     

Effect of Cu on microstructure and mechanical properties of 2519 aluminum alloy

The effect of Cu on the microstructure and mechanical properties of 2519 aluminum alloy was investigated by means of tensile test, microhardness test, transmission electron microscopy, and scanning electron microscopy. The results show that when the content of Cu is less than 6.0%, the strength of 2519 aluminum alloy increases with the increase of Cu eontent; when the content of Cu is more than 6.0%, the strength of the alloy decreases. The hardening effect of the aged alloy is accelerated at 180℃ and the time to peak age is reduced, but the plasticity of the alloy gradually decreases with the increase of Cu content. However, the hardening effect of the aged alloy decreases with the increase of Cu as the content of Cu is over 6.0%. The optimal content of Cu of 2519 aluminum alloy is 6.0%, at which the alloy has best tensile strength and plasticity.     

Microstructure evolution of components of ZAlSi8Cu3Fe alloy in processing of thixo-diecasting

The microstructures of components of ZAlSi8Cu3Fe alloy in the process of thixo-diecasting were investigated. The effects of processing conditions on the microstructure of the alloy in the thixo-diecasting procedures of original casting billets, remelting billets and casting components were researched, and the morphological evolution of α-particles in the alloy was analyzed quantitatively. The results show that, the microstructure of the original billets poured at 582 ℃ consists of rosette-like primary α-particles; in the procedure of remelting, when the temperature rises over solidus, arms in the rosette-like α-particles begin to fuse off from dendritic branches and after further heating, α-particles surrounded by liquid phase are refined by the diffusion of atoms and rounded owing to the least interface stress and interface energy principles; and in the procedure of thixo-diecasting, the morphologic characteristics of α-particles and the distribution of phases in the structure change greatly for the high shear rate under the restricted area of the ingate.     

Rapid solidification of undercooled Cu–Ge peritectic alloy

Bulk samples of Cu–14.4 wt% Ge peritectic alloy has been undercooled by up to 200 K (0.166 T_L) with a glass fluxing technique. The solidified microstructures are mainly characterized by α-Cu dendrites plus ζ phase which forms in the interdendritic areas within the whole undercooling regime. With the increase of undercooling, both the secondary arm spacing of primary α-Cu dendrite and the layer thickness of the peritectic ζ phase decrease. The primary trunk and secondary arm of α-Cu dendrites show round shape under small undercooling condition, whereas they keep a good dendritic shape within a large undercooling regime, indicating that the peritectic reaction proceeds for a relatively longer period of time in the former case. The volume fraction of peritectic ζ phase increases with undercooling, but that of α-Cu dendrite shows a decreasing tendency. Furthermore, drop tube experiments were also performed to reveal the competitive nucleation and growth mechanisms of primary α-Cu dendrite and peritectic phase ζ. Calculations based on the current dendritic growth model are made to analyze the crystal growth kinetics during the rapid solidification of undercooled Cu–Ge peritectic alloy.     

Novel preparation of big bulk-nanocrystalline Cu in large quantities

1 Introduction Bulk nanocrystalline(nc) metals, in which the grain is in nanometer range, often have some interesting properties such as increased hardness and strength, unique electronical and optical properties,which would open up a range of new applications[1, 2]. These remarkable mechanical properties of nc materials are highly desirable for structural application. To optimize the mechanical behavior, it is important to produce big-sized bulk nc metal materials in a way of lower cost and …     

Miscibility gap of B2 phase in NiAl to Cu3Al section of the Cu–Al–Ni system

The phase separation in the bcc phase of the Cu–Al–Ni system at 600–700 °C was investigated mainly by energy dispersion X-ray spectrometry (EDS) and differential scanning calorimetry (DSC). The compositions of the β₁ (A2 or B2: Cu-rich), β₂ (B2: NiAl-rich) and γ (γ-brass type) phases in equilibrium were determined. It was found that there is a β₁+β₂ miscibility gap in the β phase region as previously reported by Alexander. It was confirmed by means of high temperature in situ TEM observation that this miscibility gap consists of the B2+B2 phases but not the A2+B2 phases which is sometimes observed in many other Ni–Al and Co–Al base ternary bcc alloys. Thermodynamic calculation was performed which indicates that this characteristic feature suggests that the β₁ (B2)+β₂ (B2) miscibility gap is a part of a Cu-rich B2+NiAl-rich B2 miscibility gap island formed around the center of the composition triangle of the isothermal section. The phase separation in the β phase region and the stability of the ordered bcc aluminide are presented and discussed.     

A metallographic and quantitative analysis of the influence of stacking fault energy on shock-hardening in Cu and Cu–Al alloys

This paper deals with the mechanical behavior of Cu and solid–solution Cu–Al alloys that were shock-deformed to 10 and 35 GPa. All the shock-deformed materials showed shock-strengthening that was greater at higher shock pressure and decreased with decreasing stacking fault energy (SFE) at both shock pressures. In the literature, shock-strengthening has been qualitatively ascribed to a greater dislocation density and the formation of deformation twins without addressing the question as to why shock-strengthening is lower in low SFE materials. This question is addressed in the present work by quantifying the twin contribution to the total post-shock strength. The twin contribution was found to increase with decreasing SFE suggesting that the contribution of dislocations concurrently decreases. The stored energy of as-shock-deformed materials was measured and found to decrease with decreasing SFE implying a lower net stored dislocation density in the lower SFE alloys. It is suggested that a lower net stored dislocation density in low SFE alloys results in the observed lower shock strengthening.     

Microstructure of phases in a Cu–Zr alloy

The morphology and crystallography of phases in the Cu-0.12% Zr alloy were investigated by scanning electron microscope(SEM), transmission electron microscope(TEM), and high-resolution transmission electron microscope(HRTEM). The results show that the as-cast microstructure of Cu–Zr alloy is mainly Cu matrix and eutectic structure which consist of Cu and Cu5Zr phases with a fine lamellar structure. The disk-shaped and plateliked Cu5Zr phases with fcc structure are found in the matrix, in which habit plane is parallel to {111}a plane of the matrix.Between the copper matrix and Cu5Zr phase,there exists an orientation relationship of [112]a|| [011]Cu5Zr;(111)a||(111)Cu5Zr. The space structure model of Cu5Zr phase can be established.     

Microstructures and strength of nanoscale Cu–Ag multilayers

Cu–Ag multilayers were found to have lower peak hardness than Cu–Ni in spite of lower misfit dislocation spacing that is expected to increase the resistance of interfaces to glide dislocation transmission. This is attributed to misfit dislocation core spreading in the interface plane in Cu–Ag.     

Effect of elevated-temperature annealing on microstructureand properties of Cu−0.15Zr alloy

Cu−0.15Zr (wt.%) alloy with uniform and fine microstructure was fabricated by rapid solidification followed by hot forging. Evolution of microstructure, mechanical properties and electrical conductivity of the alloy during elevated-temperature annealing were investigated. The alloy exhibits good thermal stability, and its strength decreases slightly even after annealing at 700 °C for 2 h. The nano-sized Cu₅Zr precipitates show significant pinning effect on dislocation moving, which is the main reason for the high strength of the alloy. Additionally, the large-size Cu₅Zr precipitates play a major role in retarding grain growth by pinning the grain boundaries during annealing. After annealing at 700 °C for 2 h, the electrical conductivity of samples reaches the peak value of 88% (IACS), which is attributed to the decrease of vacancy defects, dislocations, grain boundaries and Zr solutes.     

The effect of trace elements on the sintering of Al–Cu alloys

Trace additions of Sn, In, Bi, Sb and Pb have been used to activate the liquid phase sintering of an Al–4Cu–0.15Mg alloy. Additions of as little as 0.05 wt% (∼0.01 at.%) increases the sintered density from 88 to 92% of the theoretical density. The elements which aid sintering have both high vacancy binding energies and high diffusivities in Al. It is suggested that the trace element diffuses into the Al, and forms trace element–vacancy clusters. This reduces the diffusivity of the Cu in the Al matrix, delaying Cu dissolution therefore causing the liquid to persist for longer times. This enhances sintering and therefore densification.     

Dependence of viscosity of Cu9In4 intermetallics melt on thermal history

The temperature dependence of the dynamic viscosity of Cu9In4 intermetallics melt has been investigated in five kinds of different heating and cooling processes with a torsional oscillation viscometer, It has been found that the viscosity of all Cu9In4 intermetallics decreases with increasing temperature in five kinds of different thermal processes. Thermal history has considerable effect on the viscosity. The viscosity in the cooling process with high superheating is greater than that in the cooling process with low superheating. The viscosity in the heating process is greater than that in the cooling process. No anomalous change in viscosity is measured in three kinds of cooling processes with low superheating. The anomalous change occurs at about 1050℃ in cooling with high superheating and at 800℃ in heating. Furthermore, the structural variation in different thermal processes has also been discussed on the basis of the change in viscosity and DSC analysis.     

Formation process of liquid in interface of Ti／Cu contact reaction couple

By using the Ti/Cu contact reaction couples, the dissolution behavior of Ti and Cu in the eutectic reaction process was investigated under different conditions. The results show that the formation of eutectic liquid phase has a directional property, i.e. the eutectic liquid phase forms first at the Cu side and then spreads along the depth direction of Cu. The width of the eutectic liquid zone when Ti is placed on Cu is wider than that when Ti is placed under Cu. The shape of the upside liquid zone is wave-like. This phenomenon indicates that the formation process and spreading behavior in the upside are different from those in the underside, and there exists void effect in the Cu side of underside liquid zone, this will result in the delaying phenomenon of the contact reaction between Ti and Cu,and distinctly different shapes of the both liquid zones. The formation process of Ti/Cu eutectic liquid zone is similar to that of the traditional solid-state diffusion layer, and the relationship between the width of liquid zone and holding time obeys a square root law.