Alumina Dispersion-strengthened Copper Research Articles

Preparation of high-tensile-ductility and high-conductivity alumina dispersion-strengthened copper via a cold spray additive manufacturing-friction stir processing composite process

The solid-state forming capabilities of cold spray additive manufacturing (CSAM) offer a new method for creating nano-reinforced materials. However, the interface of the deposits often fails to form strong metallurgical bonds, leading to mechanical defects that weaken the material. This study investigates the preparation of highly plastic nano-alumina dispersion-strengthened copper by combining CSAM with friction stir processing (FSP), both solid-state techniques. The results show that FSP treatment fuses the interfaces of the deposited particles, transforming the microstructure from multi-scale, elongated grains to a uniform ultrafine-grained (UFG) structure. The average grain size reduces from 3.1 μm to 0.86 μm, and the proportion of high-angle grain boundaries increases from 42.5 % to 85.2 %. This treatment significantly enhances both mechanical and electrical properties. The ultimate tensile strength increases from 210 MPa to 450 MPa, elongation at break improves from 1 % to 35 %, and electrical conductivity rises from 70 % IACS to 81 % IACS. These findings demonstrate the potential of the combined CSAM-FSP approach for producing high-performance nano-alumina dispersion-strengthened copper with superior mechanical and electrical properties.

Characteristics and Strengthening Mechanism of Texture Induced By Large Plastic Deformation for Nanostructured Alumina Dispersion Strengthened Copper Alloys

The characteristics and strengthening mechanism of the texture induced by large plastic deformation of alumina dispersion strengthened copper with 0.1 wt% Al content were investigated by electron backscattering diffraction (EBSD), transmission electron microscope (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) instrument and universal tensile testing machine. The outcomes show that the texture developed by hot extrusion with large plastic deformation is a main double fiber texture of 70% 〈001〉//X and 19% 〈111〉//X along the deformation direction (X-direction), as well as random orientations of a low fraction (11%). However, the random orientations can be completely transformed into {112} 〈111〉 Copper texture by cold work with large plastic deformation. The resulting texture reaches a 100% double fiber texture containing 70% 〈001〉//X and 30% 〈111〉//X fiber textures, and possesses high thermo-stability and high tensile strength. It can is therefore concluded that the enhanced fiber texture is an important reason for tensile strength improved by the cold work, except for grain refinement and increasing dislocation. The fiber texture strengthening is controlled by both morphology strengthening and orientation strengthening.

A practical method to improve mechanical and electrical properties of ADS copper prepared by cold spray additive manufacturing through powder pretreatment

To reduce the oxygen content on the surface of alumina dispersion-strengthened copper alloy powders, and improve properties of the deposits prepared by cold spray additive manufacturing, these powders were pretreated with hydrogen reduction treatment at 300 ℃ and 500 ℃, respectively. The microstructure and mechanical and electrical properties of the deposits before and after powder heat treatment were systematically researched. The results show that hydrogen reduction treatment can effectively reduce the oxide film on the surface of the alumina-dispersion-strengthened copper powder without changing the microstructure and mechanical properties of the powder. The alumina-dispersion-strengthened copper alloy deposit prepared from the as-received powder has obvious pores, and the tensile strength and electrical conductivity are 75 MPa and 38% IACS, while these deposits prepared from the powder treated at 300 ℃ and 500 ℃ present a dense microstructure. The tensile strengths and electrical conductivity are 202 MPa under 45% IACS and 245 MPa under 48% IACS, respectively. At the same time, the nano-Al2O3 particles are very stable under the heating and deformation conditions of adiabatic shearing by cold spraying, and the Al2O3 particles are not significantly broken during the severe plastic deformation caused by the high-speed impact of cold spraying, which enables the deposits to directly inherit the nano-dispersion strengthening structure of the powder. Therefore, it is effective to improve the mechanical and electrical properties of alumina dispersion-strengthened copper deposits by using hydrogen reduction pre-treatment to reduce the oxide film on the surfaces of the particles.

Strength and electrical conductivity behavior of nanoparticles reaction on new alumina dispersion-strengthened copper alloy

Alumina dispersion-strengthened copper (ADSC) alloy is a new materials widely used in lead frames, resistance welding electrodes, etc. The paper has systematically studied the strength and electrical conductivity behavior in situ reaction using rare-earth La and Ce. Solving the clustering on nanoparticles Al2O3 under spark plasma sintering (SPS) and addition of La and Ce for ADSC alloy is the significant differences. Specimen of Cu-0.7 wt% Al2O3 added with 0.7 wt% Ce does not present pores in SEM and BSE images due to special dispersed element Ce. A new ADSC alloy fabricated with Cu-0.7 wt%Al2O3-0.7 wt% Ce under SPS shows the high -strength and the high-conductivity. Nanoparticles Al2O3 encircled with nanoparticles CeO2 and Cu2O, which is generated in situ are evenly distributed in the Cu matrix, resulting in increasing strength. Lattice distortion does not occur in the new ADSC alloy. Cu atoms are replaced by Al generated in situ to form a solid solution with a face-centered cubic structure owing to the similar atomic radii and electronegativities of Cu and Al, resulting in increasing the electrical conductivity. Experimental results show that adding rare-earth metal nanoparticles Ce can significantly improve the properties of ADSC alloy.

Brazing of Mo to Glidcop Dispersion Strengthened Copper for Accelerating Structures.

Alumina dispersion-strengthened copper, Glidcop, is used widely in high-heat-load ultra-high-vacuum components for synchrotron light sources (absorbers), accelerator components (beam intercepting devices), and in nuclear power plants. Glidcop has similar thermal and electrical properties to oxygen free electrical (OFE) copper, but has superior mechanical properties, thus making it a feasible structural material; its yield and ultimate tensile strength are equivalent to those of mild-carbon steel. The purpose of this work has been to develop a brazing technique to join Glidcop to Mo, using a commercial Cu-based alloy. The effects of the excessive diffusion of the braze along the grain boundaries on the interfacial chemistry and joint microstructure, as well as on the mechanical performance of the brazed joints, has been investigated. In order to prevent the diffusion of the braze into the Glidcop alloy, a copper barrier layer has been deposited on Glidcop by means of RF-sputtering.

Characteristics of Nano-alumina Particles Dispersion Strengthened Copper Fabricated by Reaction Synthesis

Abstract Alumina dispersion strengthened copper (ADSC) composite was prepared by reaction synthesis (RS) process. Results show that nano-sized γ-Al2O3 particles with about 10 nm in size are homogeneously distributed in copper matrix. A coherent interface relationship with (002)Cu // (133)γ-Al2O3, and [110]Cu//[011]γ-Al2O3 characterizes along the explored interfaces of the composites. All of the interfaces are clear and closely combined with each other. The composites have high properties, the tensile strength can reach 570 MPa and the yield strength can reach 533 MPa at room temperature. Meanwhile, the softening temperature is higher than 1173 K. The electrical conductivity of the sample is 85% IACS and the Rockwell hardness can reach 86 HRB.

Characteristics of alumina particles in dispersion-strengthened copper alloys

Two types of alumina dispersion-strengthened copper (ADSC) alloys were fabricated by a novel in-situ reactive synthesis (IRS) and a traditional internal oxidation (IO) process. The features of alumina dispersoids in these ADSC alloys were investigated by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. It is found that nano-sized γ-Al2O3 particles of approximately 10 nm in diameter are homogeneously distributed in the IRS-ADSC composites. Meanwhile, larger-sized, mixed crystal structure alumina with rod-shaped morphology is embedded in the IO-ADSC alloy. The IRS-ADSC composites can obtain better mechanical and physical properties than the IO-ADSC composites; the tensile strength of the IRS-ADSC alloy can reach 570 MPa at room temperature, its electrical conductivity is 85% IACS, and the Rockwell hardness can reach 86 HRB.

Properties and Fabrication of Alumina Dispersion Strengthened Copper Alloy with High Softening Temperature

Cu-Al2O3 alloy combine both high electronic conductivity and high softening temperature. Cu-Al2O3 alloy was fabricated by internal oxidation and hot extrusion methods in the present investigation. Microstructure and properties of Cu-Al2O3 alloy was studied. The influence of preparation parameters, hot extrusion parameters and heat treatment on the properties of the alloy was investigated. The results indicated that the grain of the alloy was very small with a size between 2-10μm. Softening temperature of the Cu-0.6% Al2O3 alloy and Cu-1.0% Al2O3 alloy was 900. Cu-0.6%Al2O3 alloy and Cu-1.0% Al2O3 alloy meeting the requirements for electrode in resistance welding is the ideal substitution of the traditional electrode materials for resistance welding.

The effects of equal channel angular extrusion on the mechanical and electrical properties of alumina dispersion-strengthened copper alloys

Two alloys of alumina dispersion-strengthened copper were subjected to 1-4 passes of equal channel angular extrusion (ECAE) by route BC. Microstructures before and after deformation were characterized by scanning electron microscopy, scanning ion microscopy and electron backscatter diffraction. Mechanical and electrical properties were evaluated using uniaxial tensile testing and the four point probe method, respectively. The initial microstructure consisted of cylindrical grains, elongated in the extrusion direction and highly textured in a <100>/<111> orientation. Following four ECAE passes, the average major axis of grains in both alloys decreased by over 50%, and the microstructure approached an equiaxed morphology. The texture decreased in intensity and shifted to a <112> orientation after one ECAE pass, followed by a transition to a <101> orientation by the fourth pass. Flow stress of AL-25 and AL-60 increased only 48MPa (10%) and 24MPa (5%), respectively, while the conductivity of both alloys remained essentially unchanged. A combination of Hall–Petch strengthening and texture softening are used to explain the observed changes in mechanical behavior.

Influence of Ag Impurity Doping on the Microstructure and Hardness of Alumina Dispersion Strengthened Copper Alloys

Dispersion strengthened copper alloys (DSC) with high strength and high conductivity are widely used in automobile and electronics industries. In the present investigation the influence of Ag impurity doping on the mechanical properties of the alumina dispersion strengthened copper alloys was studied by mechanical alloying, and the influence mechanism was discussed subsequently. Alumina dispersion strengthened copper alloys powder was fabricated by high-energy ball milling. XRD results showed that the high-energy ball milling can dissolve Al2O3 into Cu matrix. As-milled powder was consolidated by cold-pressing and sintered at 860oC, 900oC, 940oC and 980oC, respectively. It was shown that the addition of Ag can significantly improve the hardness of Cu alloys. SEM characterization showed that the size of Al2O3 particles in Cu-Al2O3 sintered at 980oC was about 200nm, which is bigger than the initial size (about 150±30nm) of Al2O3 particles; and the size of Cu-Al2O3-Ag sintered at 980oC and 860oC was about 100nm and 30nm respectively. The difference in alumina size was considered as the result of Ag segregation at Cu/ Al2O3 interface. The segregation of Ag at Cu/ Al2O3 interface can suppress the growth of Al2O3, which will significantly improve the hardness of Cu alloys.

Microstructural features and properties of high-hardness and heat-resistant dispersion strengthened copper by reaction milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities, high-temperature strength and microstructure stability. To date, the state-of-art to fabrication of them was the internal oxidation (IO) process. In this paper, alumina dispersion strengthened copper (ADSC) powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling (RM) process which was an in-situ gas-solid reaction process. The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion. After the hot consolidation processes, the fully densified powder compacts can be obtained. The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction (XRD); the HRB hardness of the ADSC can be as high as 95; the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix. The electrical conductivity of the ADSC alloy is 55%IACS (International Annealing Copper Standard). The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 °C in hydrogen atmosphere. In terms of the above merits, the RM process to fabricating ADSC alloys is a promising method to improve heat resistance, hardness, electrical conductivity and wear resistance properties etc.

Precipitate Structure in an Alumina Dispersion-Strengthened Copper Base Composite Layer

A dilute copper alloy of Cu-0.45wt%Al -0.066wt %Y was selected to fabricate nanometer size Al2O3 particles dispersion-hardened composite layer by using aluminizing-internal oxidation technique. The structure and size of the precipitate, interface structure, lattice parameter mismatch and morphology were investigated by means of high resolution transmission electron microscope, analytical transmission electron microscope and image processing by VEC software. Results show that two different size and structure nano-alumina precipitate were identified as α-Al2O3 and γ-Al2O3 respectively during different processing. The precipitates possess semi-coherence or coherence interface structure to matrix with typical loop-loop contrast. The cubic γ-Al2O3 precipitate in certain crystal plane and direction parallel to the matrix。

Flow stress dependence on the grain size in alumina dispersion-strengthened copper with a bimodal grain size distribution

The grain size dependence of flow stress in Cu–2.7 vol.%Al 2O 3 (15 nm) composite with a bimodal structure was studied. It is shown that the yield strength obeys the Hall–Petch equation when an appropriate value of average grain size based on the “rule of mixture” is employed. The Hall–Petch constants ( σ 0 ɛ and k ɛ ) are proportional to strain as ɛ 0.5. An equation for flow stress as a function of true strain and average grain size is proposed. The effect of alumina nanoparticles on the yield strength is shown to be related to large amounts of dislocations density.

Tensile and fatigue fracture of nanometric alumina reinforced copper with bimodal grain size distribution

Alumina dispersion-strengthened copper was produced by an internal oxidation process and hot powder extrusion method. The microstructure of the composite consisted of fine-grained region with an average grain size of 1.1 ± 0.1 μm, coarse-grained region with an average grain size of 5.6 ± 0.1 μm, nanometric alumina particles (γ-type) with an average diameter of 30 nm, and coarse alumina particles (350 nm) at the boundaries of the large grains. The tensile and fatigue fracture of the composite was studied in the extruded condition and after 11% cold working. The low cycle fatigue behavior was examined in strain control mode ( ɛ = 0.5%) under fully reverse tension-compression cycle at 1 Hz up to 1000 cycles. High cycle fatigue was conducted using rotate-bending test up to 10 7 cycles. To reveal the role of alumina particles and the bimodal grain size structure, the tensile and fatigue fracture of extruded copper with normal grain structure was examined. It is shown that: (1) the strength and hardness of the nanocomposite are about three folders of the magnitude of the unreinforced copper; (2) fatigue strength of the nanocomposite at 10 7 cycles is about 40% higher than that of the copper; (3) both extruded copper and the nanocomposite exhibit cyclic hardening during the early stages of low cycle fatigue test which eventually approaches to a saturation stress; (4) dimple-type fracture is realized on the fracture surface of the tensile tests where dimple size decreases in the presence of the alumina particles; (5) the fatigue fracture mechanism is locally ductile deformation, microscopic void formation and coalescence.

Effect of cold rolling on properties and microstructures of dispersion strengthened copper alloys

Mechanical properties and microstructures of unidirectionally and tandem rolled alumina dispersion strengthened copper(ADSC) alloys under different conditions were investigated by tensile test, optical microscopy(OM), transmission electron microscopy(TEM) and scanning electron microscopy(SEM). For unidirectionally rolled ADSC alloys, their strengths and elongations in the longitudinal direction are higher than those in the transverse direction under both cold rolling and annealing conditions. Once fracture appears in their longitudinal stress—strain curves, sudden reduction of overall stress level before complete fracture can be observed in the transverse tensile curves. The anisotropy of mechanical properties for the ADSC alloy can be greatly improved by tandem cold rolling. And no sudden reduction of overall stress level appears in the stress—strain curves for tandem rolled ADSC alloys. The differences of their microstructures and tensile fractures were analyzed. In order to compare the differences of tensile fracture mechanism in different directions, longitudinal and transverse fracture models for unidirectionally rolled ADSC alloys were also introduced.

Tensile fracture behavior characterization of dispersion strengthened copper alloys

To well characterize alumina dispersion strengthened copper (ADSC) alloys, much work has been performed, while the effect of cold working methods on their microstructures and tensile fracture behaviors in the different directions, and corresponding fracture mechanism have not been studied systematically. In order to carry out such a systematic study, unidirectional and tandem rolling techniques were used to the ADSC alloys. The differences of tensile fracture behaviors between longitudinal and transverse directions for unidirectional rolled ADSC alloys are significant. Their mechanical properties and microstructures in longitudinal and transverse directions were studied. The C–G fracture mechanism was used to explain a sudden reduction of overall stress level in the transverse tensile curves for the unidirectional rolled ADSC alloys. Two fracture models were introduced to describe fracture processes. To reduce mechanical property anisotropy of ADSC alloys, a tandem rolling technology was proposed. Experimental results show this technology can significantly reduce the anisotropy.

Abnormal grain growth in alumina dispersion-strengthened copper produced by an internal oxidation process

Cu–2.7 vol.% Al2O3 (15 nm) composite was synthesized by an internal oxidation and hot extrusion process. The grain growth at elevated temperatures was studied and compared with extruded copper powder. Abnormal grain growth via a mechanism analogous to that of site-saturated phase transformation was observed. The critical grain size for the abnormal growth was determined to be 1.1 ± 0.2 μm. The growth rate decreased with time until the grain size approaching a final value ranging from 7.9 to 13.3 μm depending on the temperature.

Work softening characterization of alumina dispersion strengthened copper alloys

The effect of cold rolling on the hardness and microstructure of alumina dispersion strengthened copper (ADSC) alloys and oxygen free pure copper was investigated. With increased cold rolling deformation, a work softening phenomenon can be observed in ADSC alloys. The higher the alumina content is, the more difficult it is to observe the work softening phenomenon. This phenomenon is not observed in oxygen free pure copper, even after cold rolling 90%. The microstructural changes of the ADSC alloys were analyzed by TEM as a function of deformation. Initially, with an increase of the cold rolling deformation, a large number of dislocation cells are formed. Then, with further increased deformation, both a decrease of dislocation density and the formation of the smaller dislocation cells (subgrains) within the larger dislocation cells or the elongated bands are observed. Finally, as deformation attains a certain value, the smaller dislocation cells (subgrains) begin to coalesce, and the work softening phenomenon appears. All of these changes are the result of the interaction between the alumina particles and the dislocation line segments. In order to analyze the work softening mechanism for the ADSC alloys, a model is introduced in the paper.

Notch toughness evaluation of diffusion-bonded joint of alumina dispersion-strengthened copper to stainless steel

Tensile strength of the diffusion-bonded (DB) joint was as large as that of alumina dispersion-strengthened copper (DS Cu), however, the Charpy absorbed energy of the joint was considerably lower than that of DS Cu. Instrumented Charpy impact test and slow-bend Charpy test of the DB joints were performed to clarify the degradation of Charpy absorbed energy. Elasto-plastic analyses were also carried out in order to study the deformation behavior of the tensile and Charpy V-notched specimens for the DB joints. As a result, the fracture behavior of the impact and slow-bend tests was almost the same. Elasto-plastic analyses showed that the maximum strain occurred at the DS Cu apart from the interface for tensile specimen, however, the strain concentrated at the DS Cu near the interface for the Charpy notched specimen. This strain concentration arose from the mechanical heterogeneity between stainless steel and DS Cu in the bonded zone and can be attributed to the degradation of the absorbed energy of the DB joints.

Annealing behavior of alumina dispersion-strengthened copper strips rolled under different conditions

A study has been made of annealing behavior of a boron-added alumina dispersion-strengthened copper (ADSC) strip, Glidcop Al-25, and specimens fabricated by rolling of the strip by 25 to 28 pct under various conditions. All the specimens, including the starting strip, had similar microstructures consisting of microbands aligned parallel to the rolling direction. The textures of the specimens were characterized by β fiber, which runs from the copper orientation {112}〈111〉 over the S orientation {123}〈634〉 to the brass orientation {110}〈112〉 in the Euler orientation space, with the intensities in the S and the brass components being higher than the copper component and with the S components having higher intensities than the brass component in the surface layers. When annealed at 1123 K for 1 hour, the center region of the starting strip and cold-rolled specimens underwent recrystallization, with recrystallization texture being approximated by {112}〈312〉, whereas the specimens rolled at 813 K did not undergo recrystallization through the thickness. These results have been discussed based on detailed microstructures and microtextures.