Effect of milling time in characteristics of the powder Cu-5wt.%Graphite

Composites of Cu-5wt.%Graphite were prepared by high-energy milling, under argon atmosphere for milling time of up to 50 h, to investigate the influence of the milling time on the size and dispersion of the copper and carbon phases. The formation of a monophasic carbon-copper solid solution was also investigated. The powder samples were collected at different times and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM and FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Composite particles were formed by fragments of graphite embedded in the soft Cu matrix. After 50 h of milling, the Cu phase had a crystallite size of 24 nm and micro-strain of 0.26 %. The lattice parameter showed a reduction of 0.001545 nm and reached a value of 0.360152 nm. Furthermore, no carbon diffraction peak was observed in the milled powders, due to the small graphite crystallites. Meanwhile, the Raman spectra showed that the carbon phase remains crystalline, even after 50 h of milling. When the composite was annealed at 600 °C, for 1 h and under argon atmosphere, no carbon precipitate was observed. These results suggest the absence of the formation of a solid solution of carbon in copper.     

Preparation and mechanical properties of SiC-reinforced Al6061 composite by mechanical alloying

In this paper, an Al6061–10 wt% SiC composite was prepared using the mechanical alloying route. The morphology and the structure of the prepared powder, which change with milling time, were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, respectively. Moreover, the relationships among the stages of mechanical alloying (MA), relative density and hardness of both pressed and hot extruded materials were investigated. The morphological evolutions showed that relatively equiaxed powders could be synthesized after 9 h of milling. The evolution of relative density and hardness with milling time is due to the morphological and microstructural changes imposed on the composite powder. High-relative densities are typical of the hot extruded samples. The effect of mechanical alloying process on hardness is more significant compared to reinforcement particles. The aging behaviors of the mechanically alloyed, commercially mixed and unreinforced Al6061 were compared. The results showed that MA composites exhibit no aging-hardenability.     

Effects of TiB2 on microstructure of nano-grained Cu–Cr–TiB2 composite powders prepared by mechanical alloying

Nano-grained CuCr25 and CuCr25–(2 wt%–10 wt%)TiB₂ composite powders were prepared by mechanical alloying method. The milled powders were characterized by SEM, FSEM, EDS, XRD, TEM and HTEM. The results indicate that average grain size of Cu, Cr and TiB₂ are less than 50 nm and each component disperses uniformly. The grain size of Cu and Cr decreased and the lattice distortion increased gradually as the TiB₂ content increased from 2 wt% to 10 wt%. The ultrafine TiB₂ particles play the role of “micro-milling balls” to compact, micro-etch, micro-frict and micro-cut with Cu and Cr so that the grain refinement and lattice strain are promoted.     

Mechanical alloying and sintering of nanostructured TiO2 reinforced copper composite and its characterization

Mechanical alloying is a suitable method for producing copper based composites. Cu–TiO₂ composite was fabricated using high energy ball milling and conventional consolidation. Ball milling was performed at different milling durations (0–24 h) to investigate the effects of the milling time on the formation and properties of produced nanostructured Cu–TiO₂ composites. The amount of the TiO₂ in the final composition of the composite assumed to be 0, 1, 3, 5 and 7 wt%. The milled composite powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy to investigate the effects of the milling time on the formation of the composite and its properties. Also hardness, density and electrical conductivity of the sintered specimen were measured. High energy ball milling causes a high density of defects in the powders. Thus the Cu crystallite size decreases, generally to less than 50 nm. The maximum hardness value (105 HV) of the sintered compacts belongs to Cu–5 wt%TiO₂ which has been milled for 12 h.     

Processing of Cu-Fe and Cu-Fe-SiC nanocomposites by mechanical alloying

The Cu-Fe and Cu-Fe-SiC nanocomposite powders were synthesized by a two step mechanical alloying process. A supersaturated solid-solution of Cu-20 wt% Fe was prepared by ball milling of elemental powders up to 5 and 20 h and subsequently the SiC powder was added during additional 5 h milling. The dissolution of Fe into Cu matrix and the morphology of powder particles were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that the iron peaks in the XRD patterns vanish at the early stages of mechanical alloying process but the dissolution of Fe needs more milling time. Moreover, the crystallite size of the matrix decreases with increasing milling time and the crystallite size reaches a plateau with continued milling. In this regard, the addition of SiC was found to be beneficial in postponing the saturation in crystallite size refinement. Moreover, the effect of SiC on the particle size was found to be significant only if it is added at the right time. It was also found that the silicon carbide and iron particles are present after consolidation and are on the order of nanometer sizes.     

Structural characterization and creep resistance of nano-silicon carbide reinforced Sn–1.0Ag–0.5Cu lead-free solder alloy

Nano-sized, non-reacting, non-coarsening SiC particles were successfully fabricated by high energy ball milling. Mechanically mixing was adopted to prepare SiC-particulate reinforced Sn–1.0Ag–0.5Cu (SAC105) composite solders. The effects of SiC addition on the melting behavior, microstructure and the corresponding creep properties were explored. It is found that the addition of 0.35–0.75 wt.% SiC nano-sized particles can effectively decrease the undercooling, while the melting temperature is sustained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process. After the addition of 0.35% SiC nano-particles, a fine microstructure of Ag₃Sn and Cu₆Sn₅ IMCs with small spacing appeared in the β-Sn matrix. Moreover, the creep rate of the composite solder exhibited a consistently lower value than that of plain SAC(105) solder due to a second phase dispersion strengthening mechanism as well as a refinement of IMCs. Hence, the composite SAC(105)/0.35% SiC solder displayed a higher creep resistance (3.1 times) and fracture lifetime (3 times) than that of plain solder. However, this effectiveness is reduced when 0.75% SiC addition starts constricting the growth Ag₃Sn and Cu₆Sn₅ IMC and forming a weak interface with the enlarged β-Sn matrix.     

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al₄C₃ and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl₂O₄ in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution.     

Wear behavior of Al–Cu and Al–Cu/SiC components produced by powder metallurgy

In the present study, the dry sliding wear behavior of some powder metallurgy (P/M) Al–Mg–Cu alloys with different weight percentage of Cu (0, 1, 2, 3, 4, and 5 wt%) and corresponding metal matrix composites reinforced with 5 or 10 vol% silicon carbide particles (SiC) have been carried using pin-on-disk apparatus. The tested specimens were tested against hardened steel disk as a counter face at room conditions (∼20 °C and ∼50% relative humidity). The normal load was 40 N and sliding velocity of counter face disk was 150 rpm (0.393 m/s) and total testing time of 60 min, which corresponds to a distance of 1414 m. Generally, both hardness and wear resistance were enhanced by the addition of Cu and/or SiC to the Al-4 wt% Mg alloy. The formations of mechanically mixed layer (MML) as a result of material transfer from counter face disk to the samples and vice versa were observed in all tested specimens.     

Effect of variation in physical properties of the metallic matrix on the microstructural characteristics and the ageing behaviour of Al-Cu/SiC metal matrix composites

In this study, aluminium-based metallic matrices with varying amount of copper (1 wt% Cu and 4.5 wt% Cu) were reinforced with SiC particulates using a partial liquid phase casting technique. The results of the present investigation showed smaller sized and higher weight percent of SiC particulates being successfully incorporated with a decrease in the weight percent of copper in the matrix. Microstructural characterisation studies conducted on the composite samples revealed an increase in uniformity of distribution of SiC particulates, improved SiC/Al interfacial integrity and smaller grain size of the metallic matrices with decreasing weight percent of copper. Results of the microstructural characterisation studies also exhibited the presence of solute rich zone in the near vicinity of SiC particulates and the nucleation of secondary phases both at and in near vicinity of SiC particulates. The result of the ageing studies revealed an accelerated ageing kinetics for the Al-1%Cu/SiC composite when compared to the Al-4.5%Cu/SiC composite samples. The results of accelerated ageing kinetics were rationalised in terms of the effect of variation in the physical properties of the metallic matrix and the ensuing microstructural characteristics due to variation in the amount of copper in the matrix.     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Fabrication of SiC particles-reinforced magnesium matrix composite by ultrasonic vibration

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase Mg₁₇Al₁₂ varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy.     

Characterization of cemented Cu matrix composites reinforced with SiC

In this study, some properties of copper produced by cementation method and its composites reinforced with 1wt%, 2wt%, 3wt% and 5wt% SiC particles, produced by powder metallurgy method, were investigated. Composite powders were pressed by applying an uniaxial pressure of 280 MPa and sintered at temperatures of 700 °C for 2 h embedding in graphite powder. Scanning electron microscope (SEM-EDS), X-ray diffraction (XRD) techniques were used to characterize the Cu and SiC which are dominant components in the sintered composites. Microstructure studies revealed that SiC particles were located around the copper particles. The relative densities of Cu-SiC composites determined by Archimedes’ principle decreased from 98.11% to 90.93% with increasing reinforcement components. Measured hardness of sintered compacts varied from 127 to155 HVN. Maximum electrical conductivity of test materials ranged from 80.17% IACS to 57.76% IACS.     

Magnetic properties of magnetically soft nanocomposite Co-SiO2 prepared via mechanical milling

Nanocomposite of Co-SiO2, a soft magnetic material, with Co weight fraction x = 0.3 and 0.7 was prepared via mechanical milling. The magnetic properties of these samples, both zero-field-cooled (ZFC) and field-cooled (FC), have been measured as a function of x, milling time, and temperature. The structural assessment of the composite indicates a presence of only ferromagnetic (FM) hcp-Co phase in the composite. However, reported magnetic properties of these composites appear to be dependent on the presence of antiferromagnetic (AFM) phases of cobalt oxide as well. The observed enhancement in ZFC coercivity and a reduction in saturation magnetization with the milling time are due to an increase in defect density upon milling. The ZFC coercivity for the x = 0.3 samples has been found to be much higher than the x = 0.7 samples for all milling times. The coercivity above 50 K depends on temperature according to the law corresponding to isotropic uniaxial superparamagnetic particles. Below 50 K the presence of an AFM phase Co3O4 (TN approximately 33 K) and increased interparticle interactions bring in a departure from that law. The saturation magnetization is found to be temperature dependent for the x = 0.3 samples and temperature independent for the x = 0.7 samples, which further provides evidence of the presence of higher AFM phase fraction in the composite with a low metal volume fraction. The FC magnetic measurements show a presence of an exchange bias field and an enhanced coercivity which are higher than the ZFC measurements. All magnetic measurements indicate that the overall magnetic properties of the composite are dictated by the presence of a trace amount of cobalt oxides.     

Microstructures and mechanical properties of spark plasma sintered Cu–Cr composites prepared by mechanical milling and alloying

Nanograined Cu–8 at.% Cr composite was produced by a combination of mechanical milling (MM), mechanical alloying (MA) and spark plasma sintering (SPS). Commercial Cu and Cr powders were pre-milled separately by MM. The milled Cu and Cr powders were then mechanically alloyed with as-received Cr and Cu powders respectively. After milling, the powder mixtures were separately subjected to SPS. It was found that pre-milling Cr can efficiently decrease the size of grain and reinforcement, resulting in remarkable strengthening. The grain size of Cu matrix was about 82 nm after SPS. The Vickers hardness, compressive yield strength and compression ratio of the composite were 327 HV, 1049 MPa and 10.4%, respectively. The excellent mechanical properties were primarily attributed to dispersion strengthening of the Cr particles and fine grain strengthening of the Cu matrix. The strong Cu/Cr interface and dissolved Cr atoms can also contribute to strengthening of the composite.     

Effect of powder characteristics on Cr internal oxidation for preparation of Cr2O3/Cu composite

Abstract

Cr O₃/Cu composite was prepared by the internal oxidation of Cu–Cr pre-alloyed powders formed by high energy milling. Effects of milling time on the internal oxidation characteristics of Cu–Cr pre-alloyed powders were also discussed in this paper. The results indicate that the degree of the internal oxidation continually increases with prolonged milling time. At the initial stage, external oxidation rather than internal oxidation occurs, resulting in coarse Cr₂O₃ particles. With further milling, the internal oxidation becomes more complete and the sizes of Cr₂O₃ particles also become finer and well distributed. The properties of the composite are therefore improved. A high quality composite specimen from Cu–1·0Cr pre-alloyed powders after 40 h milling was prepared by the internal oxidation process. The Cr₂O₃ particles with an average size of 2–5 μm in diameter and about 5–10 μm in particles space were found by a microstructure examination, and they were uniformly dispersed in the Cu matrix.     

Study of the influence of TiB2 particles on the melt structure of the hypoeutectic Al–Cu alloy by small angle X-ray scattering

Small angle X-ray scattering (SAXS) studies were carried out in Shanghai Synchrotron Radiation Facility (SSRF) to study the effect of addition of TiB₂ particles on the melt structures of Al-15 wt% Cu. It was found that doping with TiB₂ particles could dramatically reduce the sizes of the melt aggregates at temperatures ranging from the melting point to 800 °C. The results show that the aggregates in the Al–Cu melt present mass fractal characteristics and distribution of incompact 3D flocs.     

Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

Effect of heat treatment on microstructure and interface of SiC particle reinforced 2124 Al matrix composite

The microstructure and interface between metal matrix and ceramic reinforcement of a composite play an important role in improving its properties. In the present investigation, the interface and intermetallic compound present in the samples were characterized to understand structural stability at an elevated temperature. Aluminum based 2124 alloy with 10 wt.% silicon carbide (SiC) particle reinforced composite was prepared through vortex method and the solid ingot was deformed by hot rolling for better particle distribution. Heat treatment of the composite was carried out at 575 °C with varying holding time from 1 to 48 h followed by water quenching. In this study, the microstructure and interface of the SiC particle reinforced Al based composites have been studied using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), electron probe micro-analyzer (EPMA) associated with wavelength dispersive spectroscopy (WDS) and transmission electron microscopy (TEM) to identify the precipitate and intermetallic phases that are formed during heat treatment. The SiC particles are uniformly distributed in the aluminum matrix. The microstructure analyses of Al–SiC composite after heat treatment reveal that a wide range of dispersed phases are formed at grain boundary and surrounding the SiC particles. The energy dispersive X-ray spectroscopy and wavelength dispersive spectroscopy analyses confirm that finely dispersed phases are CuAl₂ and CuMgAl₂ intermetallic and large spherical phases are Fe₂SiAl₈ or Al₁₅(Fe,Mn)₃Si. It is also observed that a continuous layer enriched with Cu and Mg of thickness 50–80 nm is formed at the interface in between Al and SiC particles. EDS analysis also confirms that Cu and Mg are segregated at the interface of the composite while no carbide is identified at the interface.     

Effect of microstructural features on the ageing behaviour of Al–Cu/SiC metal matrix composites processed using casting and rheocasting routes

In the present study, microstructural variation in Al–2 wt% Cu/SiC composites was accomplished by synthesizing them using conventional casting and partial liquid phase casting (rheocasting) routes. Microstructural characterization studies conducted on the rheocast composite samples revealed a finer grain size, minimal porosity, uniform distribution of SiC particulates, and a superior matrix – particulate interfacial integrity when compared to the conventionally cast composite samples. Furthermore, the results of interfacial characterization studies revealed that the presence of porosity associated with either individual SiC particulate or SiC clusters significantly influence the constitutional characteristics of the interfacial region. Results of ageing studies revealed an accelerated ageing kinetics in case of rheocast samples when compared to the conventionally cast composite samples. The results of ageing studies were finally rationalized in terms of the difference in microstructural characteristics of the rheocast and conventionally cast composite samples. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of SiC particles distribution on mechanical properties and fracture of DRA alloys

In the last 20 years a new class of metal matrix composite material (DRA – Discontinuously Reinforced Aluminum) with aluminum alloy matrix and SiC particles as secondary phase has been developed. The most important step during composite production is the homogenization process of metal and ceramic powder particles. Quantitative analysis of a SiC particles distribution in the aluminum alloy matrix (CW67) was used to determine the optimum homogenization parameters of different powders. It was found out that the level of mixture homogeneity largely depends on the amount of mixing dish filling, homogenization time and characteristics of reinforcing particles. By introducing the concept of homogeneity index, it was shown that the lowest values of the mentioned parameter correspond to the best uniformity of SiC particles in the CW67 matrix. Composite with the lowest value of homogeneity index was the one with 5 vol.% of SiC, homogenized during 60 min and the amount of mixing dish filling of 20 vol.%. This composite displayed the best values of mechanical properties and fracture resistance.