Shift-speed Ball Milling Research Articles

Microstructure and Properties of Aluminum-Graphene-SiC Matrix Composites after Friction Stir Processing.

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites.

Highly Dispersed Cu Produced by Mechanical Stress-Activated Redox Reaction to Establish Galvanic Corrosion in Fe Implant.

Fe has immense potential for biodegradable orthopedic applications, but it degrades slowly in the physiological environment. Inducing galvanic couple by alloying Cu to Fe using ball milling is a promising approach. However, the ductile nature of Cu leads to the cold welding of a large amount of Cu powder during ball milling, which makes it difficult to disperse uniformly in the Fe matrix. Here, a Fe-CuO implant with highly dispersed Cu particles in the matrix was developed by shift-speed ball milling and selective laser melting. Specifically, copper oxide (CuO) particles were selected as precursors and dispersed in Fe powders by ball milling since they were brittle and would not be cold-welded during ball milling. After further milling in higher energy, it was found that CuO particles reacted with Fe and generated Cu particles through a stress-activated redox reaction. Subsequently, the obtained powders were prepared into a Fe-CuO implant using selective laser melting. Microstructure examination revealed that the Cu phases in the implant were dispersed evenly in the Fe matrix, which was considered to establish a large number of galvanic couples and aggravated the galvanic corrosion tendency. Electrochemical tests indicated that the implant had improved performance in degradation behavior in terms of high corrosion current density (22.4 μA/cm2), low corrosion resistance (1319 Ω cm2), and good degradation stability. In addition, it presented antibacterial effects against Escherichia coli and Staphylococcus aureus by diffusion mechanisms with killing rates of 90.7 and 96.7%, respectively, as well as good cytocompatibility.

Preparation and properties of lead-free FeS/Cu-Bi composites by flake powder metallurgy via shift-speed ball milling

Lead-free FeS/Cu-Bi (FCB) self-lubricating composites were prepared via shift-speed ball milling (SSBM) and powder metallurgy. The microstructure and evolution of mixed powders were studied, and the mechanical and tribological properties of the FCB composites were tested. SSBM includes long-term low-speed ball milling (LSBM) and short-term high-speed ball milling (HSBM). In the early LSBM, the matrix phase CuSn10 powder was flattened into flakes, and the lubricating phases FeS and Bi were refined and gradually dispersed on the CuSn10 flakes. After short-term HSBM, FeS and Bi were further trapped on the CuSn10 flakes, which not only improved the bonding performance between the lubricating phase and copper alloy but also protected the continuity of the copper alloy matrix from additional damage. 6 + 1 h SSBM (6 h LSBM + 1 h HSBM) improved the mechanical properties, antifriction and wear resistance of FCB composites. Compared with traditional HSBM, SSBM provides a new way to prepare FCB self-lubricating composites with better comprehensive properties.

Tailoring Cu nano Bi self-lubricating alloy material by shift-speed ball milling flake powder metallurgy

A novel method for preparing lead-free Cu nano Bi (CNB) alloy materials by nano Bi powder and shift-speed ball milling (SSBM) flake powder metallurgy was proposed. To improve the mechanical and tribological properties of the alloy materials, the spherical CuSn10 powder was firstly extruded and sheared into flakes by low-speed ball milling (LSBM) in the SSBM system. Meanwhile, the nano Bi powder was evenly dispersed and coated on the CuSn10 flakes. The mechanical alloying between mixed powders and the cold welding of flake CuSn10 flakes containing nano Bi into layered particles were then realized through short-time high-speed ball milling (HSBM) in the SSBM system. While promoting the uniform dispersion of lubricating phase Bi, the surface area of matrix CuSn10 flake was increased so as to achieve better combination of CuSn10 matrix in the material. Results show that the mechanical properties of the CNB material prepared through nano Bi powder and SSBM flake powder metallurgy improved compared with the Cu-Bi material prepared by HSBM. In addition, the antifriction and wear resistance improved by 30% and 80%, respectively.

Microstructural characteristic and mechanical properties of the in-situ MgAl2O4 reinforced Al matrix composite based on Al-Mg-ZnO system

In-situ synthesized Al matrix composites (AMCs) have drawn lots of interest recently relying on the designability of reinforcement configurations and promising mechanical properties. In this work, a new generation of AMCs reinforced by in-situ MgAl2O4 particles was fabricated based on Al-Mg-ZnO system using shift-speed ball-milling (SSBM) combined with reactive sintering method. The detailed microstructural characterization and comprehensive thermodynamic analysis rationalized the in-situ reaction mechanism, in which the substituted MgO was involved in the formation of homogeneously dispersed MgAl2O4 that forms robust interfacial bonding with matrix. In addition, the coefficient of thermal expansion mismatch strengthening and grain refinement acted in concert to render the impressive mechanical properties, achieving the yield stress of 347 MPa and ultimate tensile stress of 505 MPa. This work can be informative for the fabrication of high-performance in-situ MgAl2O4 reinforced AMCs based on Al-Mg-oxides system.

Progress of Flake Powder Metallurgy Research

This paper reviewed several recent progresses of the new powder metallurgy technology known as flake powder metallurgy (FPM) including different processing routes, conventional FPM (C-FPM), slurry blending (SB), shift-speed ball milling (SSBM), and high-shear pre-dispersion and SSBM (HSPD/SSBM). The name of FPM was derived from the use of flake metal powders obtained by low-speed ball milling (LSBM) from spherical powder. In this case, the uniformity of reinforcement distribution leads to increased strength and ductility. Powder is the basic unit in PM, especially advanced PM, and its control is key to various new PM technologies. The FPM is a typical method for finely controlling the powder shape through low-energy ball milling (LEBM) to realize the preparation of advanced material structures. The present paper represents a review of the main results of research on FPM and indicates the potential for future studies devoted to the optimization of this processing route.

Revealing the strengthening and toughening mechanisms of Al-CuO composite fabricated via in-situ solid-state reaction

Due to native deficiency of the interfacial mismatch between Al2O3 and Al-melt, as well as micron-Al2O3 segregation at matrix grain boundaries (GBs), achieving both high strength and fracture toughness has been the long-lasting challenge for Al-CuO composite fabricated by conventional casting. Herein, we report a novel manufacturing of Al-CuO composite via shift-speed ball-milling (SSBM) of Al-5 wt.% CuO powders and afterwards subjected to hot-pressing (HP) as well as heat treatment. Comprehensive characterization shows that in-situ generation of the two types of Al2O3 with intragranular distribution, including δ*-Al2O3 particles (~200 nm) and γ-Al2O3 whiskers (length of ~150 nm, thickness of ~20 nm), was governed by a diffusion-assisted nucleation-regime ascribing to the intense thermal effect of Al-CuO reaction. The size and spatial distribution of Al2O3 were emphasized to address their contribution to the high mechanical performance of the composite, which exhibits a tensile strength of ~481 MPa and fracture elongation of ~16.8 %. Meanwhile, the toughening mechanism of present Al-CuO composite was rationalized on basis of the "dislocation punched zone" and "plastic zone" affected by Al2O3. Both the theoretical analysis and fracture morphology support a reinforcements-matrix interface failure mechanism and the non-uniform distribution of Al2O3 consisting alternant "rich/poor zones" can markedly contribute to the high toughness. The present findings may provide a promising strategy to achieve an intragranular distribution of nano-sized reinforcements in Al-metal oxides composites, which enables increasing strength and ductility of the metal matrix.

Synthesis of carbon nanotube reinforced Al matrix composite coatings via cold spray deposition

For the fabrication of high-strength carbon nanotube (CNT) reinforced Al matrix composites, the uniform dispersion, strong interface bonding and high structural integrity of CNTs have been regarded as the three most important issues. In this work, two distinct approaches, namely high shear dispersion (HSD) and shift-speed ball milling (SSBM), were applied to disperse CNTs (1.5 wt%) into pure Al powders. These two kinds of CNT/Al composite powders as well as the pure Al powder (as a comparison) were deposited onto stainless steel plates by cold spraying using different processing parameters. The velocity and the temperature of the particle prior to impact was simulated by the commercial code of Fluent. The deposition efficiency, microstructure evolution, as well as the distribution and structural integrity of CNTs in the composite coatings produced from different starting powders were comparatively investigated in terms of X-ray diffraction (XRD), Raman spectra, and electron back scanning diffraction (EBSD). According to the XRD and Raman analysis, no new phases such as oxides or brittle Al4C3 were detectable in both CNT/Al composite coatings. Some structural damages of CNTs were found in both composite coatings, especially the one fabricated from HSD composite powder. The dispersion of CNTs onto Al particle surfaces by HSD approach did not achieve a significant strengthening effect on the composite coatings, but adversely affected the metallic bonding of the particles and the substrate. The microhardness of the CNT/Al composite coating produced from SSBM powders reached around ~115 HV0.1, showing a significant improvement compared to the pure Al coating mainly due to the grain refinement and CNTs strengthening.

Revealing the Strengthening and Toughening Mechanisms of Al-CuO Composite Fabricated Via In-Situ Solid-State Reaction

Due to native deficiency of the interfacial mismatch between Al>sup>2O3 and Al-melt, as well as micron-Al2O3 segregation at matrix grain boundaries (GBs), achieving both high strength and fracture toughness has been the long-lasting challenge for Al-CuO composite fabricated by conventional casting. Herein, we report a novel manufacturing of Al-CuO composite via shift-speed ball-milling (SSBM) of Al-5 wt.% CuO powders and afterwards subjected to hot-pressing (HP) as well as heat treatment. Comprehensive characterization shows that in-situ generation of the two types of Al2O3 with intragranular distribution, including δ*-Al>sup>2O3 particles (~200 nm) and γ-Al>sup>2O3 whiskers (length of ~150 nm, thickness of ~20 nm), was governed by a diffusion-assisted nucleation-regime ascribing to the intense thermal effect of Al-CuO reaction. The size and spatial distribution of Al2O3 were emphasized to address their contribution to the high mechanical performance of the composite, which exhibits a tensile strength of ~481 MPa and fracture elongation of ~16.8 %. Meanwhile, the toughening mechanism of present Al-CuO composite was rationalized on basis of the dislocation punched zone and plastic zone affected by Al2O3. Both the theoretical analysis and fracture morphology support a reinforcements-matrix interface failure mechanism and the non-uniform distribution of Al>sup>2O3 consisting alternant rich/poor zones can markedly contribute to the high toughness. The present findings may provide a promising strategy to achieve an intragranular distribution of nano-sized reinforcements in Al-metal oxides composites, which enables increasing strength and ductility of the metal matrix.

High-content graphene nanoplatelet reinforced aluminum composites produced by ball milling and hot extrusion

Due to the high specific surface area of graphene, the effective incorporation of high-content graphene in metals is challenging. Here, aluminum composites with graphene nanoplatelet (GNP) content up to 5.0 vol% were prepared by spark plasma sintering (SPS) of blended powders with various ball milling regimes and subsequent hot extrusion. The effects of GNP distribution state on the properties of GNP/Al composite were investigated. 5.0 vol% GNPs were uniformly dispersed in aluminum matrix by high-speed ball milling (HSBM) process, but with damage GNPs due to the too high energy input. By contrast, the wellstructured and dispersed GNPs in aluminum powders were obtained via shift-speed ball milling (SSBM). The clear GNP-Al interface in extruded SSBM composite was attributed to well-structured GNPs. As a result, the yield strength (YS) and ultimate tensile strength (UTS) of composite produced by SSBM reached 279 and 303 MPa, which are 166% and 116% higher than those of monolithic Al. This demonstrated that it may be promising to introduce high-content GNPs with tailorable interface in Al alloys via modified ball milling technique and hot extrusion.

Superior Mechanical Performance of Inductively Sintered Al/SiC Nanocomposites Processed by Novel Milling Route

This paper explores new routes for flake powder metallurgy, with the aim of designing an effective route for fabricating metal matrix nanocomposites, combining high strength and good ductility. A new route that uses three speeds, instead of the two speeds characterizing the shift-speed ball milling (SSBM) route, has been suggested and implemented. The mechanisms of these routes were illustrated based on the intensity of ball-powder-ball collisions and the morphology evolution. The ball milled powder were characterized using filed emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and Energy dispersive spectroscopy (EDS) to investigate the morphology evolution of the composites powder and the homogenous distribution of the SiC nanoparticles within the Al matrix. The reinforcing adequacy and interfacial bonding of 2 wt.% SiC nanoparticles in an inductively sintered composite has been investigated. Mechanical testing of the produced bulk composites resulted in achieving superior mechanical properties, characterized by 92% higher hardness, 180% higher yield strength, 101% higher ultimate strength, and 0% loss in uniform elongation, compared with those of regular SSBM. This is attributed to the homogeneous dispersion of the reinforcement into the Al matrix.

Microstructural Evolution and Mechanical Properties of Multiwall Carbon Nanotubes Reinforced Titanium-Based Nanocomposites Developed by Spark Plasma Sintering

In this study, the role of multiwall carbon nanotubes (MWCNT) on the microstructural evolution and mechanical properties of Ti6Al4V-based composites was investigated. This was conducted by dispersing different concentrations (0.5, 1.0 and 1.5 wt%) of MWCNT into the Ti6Al4V matrix using shift-speed ball milling technique. Thereafter, the Ti6Al4V and the nanocomposites were consolidated via the spark plasma sintering technique. Various characterization techniques; scanning electron microscopy (SEM), transmission electron microscopy (TEM) and light microscopy were conducted to understand the microstructural evolution of the samples after the dispersion and sintering process. Subsequently, micromechanical and nanoindentation was carried out to reveal the mechanical properties of the fabricated samples. The morphological examination using SEM and TEM revealed the dispersibility of MWCNT dispersed within the Ti6Al4V matrix. Besides, the selected area diffraction and the fast Fourier Transform pattern demonstrated that the increase in concentration of the MWCNT exposed the nanotubes to adverse stresses during the dispersion process. Furthermore, the incorporation and increase in concentration of the MWCNT in the titanium alloy resulted in microstructural and phase changes, which translate to tremendous improvements in microhardness, nanohardness and elastic modulus up to 46.9%, 150.8%, and 169.5% respectively.

Regulating Mechanical Properties of Al/SiC by Utilizing Different Ball Milling Speeds

Advanced materials with high strength are in great demand for structural applications, such as in aerospace. It has been proved that fabrication strategy plays a vital role in producing composites to satisfy these needs. This study explores new strategies for flake powder metallurgy, with the aim of designing an effective strategy to achieve the highest possible mechanical strength for a metal matrix nanocomposite without changing the reinforcement fraction. Different strategies were used to regulate the mechanical properties for similar composites based on shift speed ball milling. Ultra-ductile composites on one hand, and ultra-strong composites on the other hand, were fabricated using similar composites. The results demonstrate that shifting the ball milling speed can be used to manipulate the mechanical properties of the composite to achieve the desired properties for any specific application.

Effect of SiC nanoparticles on the precipitation behavior and mechanical properties of 7075Al alloy

In terms of aluminum alloy matrix composites, the effect of reinforcement on precipitation is worth investigating. In this work, the silicon carbide nanoparticles-reinforced 7075Al (SiCnp/7075Al) composite was fabricated through a series of powder metallurgy procedures, shift-speed ball milling, hot pressing, and hot extrusion, and the precipitation behavior of SiCnp/7075Al composite was compared with that of 7075Al alloy after T6 treatment. The results show that only a small addition (1 vol%) of SiCnp modifies the morphology and dispersion of precipitates. The uniformly dispersed small precipitates (η′ phase) and increased dislocation density have a positive influence on the mechanical properties of composites. Based on the fracture surface and element composition, a fracture mode dominated by precipitated phase-induced crack initiation was proposed. This study suggests a promising approach to design the alloy matrix composites through controlling the behavior of precipitated phases with nano-reinforcement.

Achieving ultra-high strength and good ductility in AZ61 alloy composites containing hybrid micron SiC and carbon nanotubes reinforcements

In this work, the multi-scaled micron SiC and carbon nanotubes (CNTs) reinforced AZ61 matrix composites were successfully fabricated by powder metallurgy method followed by hot extrusion. The CNTs were adsorbed onto the surface of the micron SiC particles through hydrogen bonding caused by the groups functionalized on the surface of SiC particles (hydroxyl (-OH)) and CNTs (carboxyl (-COOH)), and then a shift speed ball milling was used to disperse the CNTs uniformly in the matrix. The microstructure characterization showed that this method could maintain the structural integrity of the CNTs, and the hybrid reinforcements could significantly refine the grain size of the matrix. In addition, the basal texture of the composites was weakened gradually as the content of the reinforcement increased. Microstructural investigation revealed that fine MgO formed by in-situ reaction between the oxygen groups and the magnesium matrix resulted in enhanced interfacial bonding. The ultra-high strength and good ductility (ultimate tensile strength: 412 MPa, yield strength: 345 MPa, and elongation: 8.0%) were achieved in the AZ61-5SiC-0.5CNTs composite. The significantly improved strength of the composites was mainly attributed to the synergistic influence of grain refinement, load transfer and increased dislocation density in the matrix due to thermal mismatch while the good ductility can mainly be attributed to the weakened basal texture. This work introduces a method of coupling a novel processing method with hybrid reinforcements approach to develop magnesium matrix composites with high strength and good ductility.

Fabrication and mechanical properties of CNT/Al composites via shift-speed ball milling and hot-rolling

Abstract

Evaluation of the sinterability, densification behaviour and microhardness of spark plasma sintered multiwall carbon nanotubes reinforced Ti6Al4V nanocomposites

Abstract Structural and industrial demands for lightweight engineering materials with exclusive properties have been rising in recent decades for automobile and aerospace applications. This has encouraged various innovations in materials engineering communities to synthesis advanced engineering materials using improved fabrication technique such as spark plasma sintering (SPS). In this study, titanium-based nanocomposites were synthesized by reinforcing Ti6Al4V reinforced with (0.5, 1.0 and 1.5 wt%) multiwall carbon nanotubes (MWCNT) powders. The starting powders were blended by shift-speed ball milling. Thereafter, SPS technique was used to consolidate the admixed powders by employing the following sintering parameters; sintering rate, 100 °C/min, compressive pressure, 50 MPa, holding time, 10 min and sintering temperatures of 900–1100 °C. The influence of MWCNT additions on the sinterability, densification behaviours and microhardness of the sintered nanocomposites were investigated. The results revealed that the densification of the sintered nanocomposites was in the range of 97.51–99.61% which decreased with an increase in concentration of the MWCNT. Meanwhile, the densification and microhardness improved tremendously with an increase in sintering temperatures.

Tailoring the structure and mechanical properties of graphene nanosheet/aluminum composites by flake powder metallurgy via shift-speed ball milling

Graphene nanosheet (GNS)/aluminum composites were fabricated via shift-speed ball milling (SSBM), consisting of a long-term low-speed ball milling (LSBM) and a short-term high-speed ball milling (HSBM). During the early stage of LSBM, Al powders were flattened into flakes, while the agglomerated GNSs were gradually dispersed onto Al flakes. After an inflection point of LSBM time, the dispersed GNSs got re-agglomerated and seriously damaged due to the accumulated work-hardening of Al flakes. During HSBM, the GNS/Al flakes were cold-welded into lamellar-structured particles, preserving the GNS dispersion states. It was demonstrated that the 0.5 vol.% GNS/Al composites via SSBM with 6 h LSBM had proper combination of ultrafine-grained Al matrices with well-preserved, uniformly-dispersed GNSs. Exceptional properties were achieved with a good ductility of 13.5% at a tensile strength of 295 MPa. Therefore, such flake powder metallurgy via SSBM proved to be a smart and effective fabrication strategy for nano-reinforced metal matrix composites.

Design of an efficient flake powder metallurgy route to fabricate CNT/6061Al composites

A flake powder metallurgy route that combines high-shear pre-dispersion process with shift-speed ball milling was designed to fabricate carbon nanotube reinforced aluminum composites. In order to mitigate the dispersion responsibility of ball milling and improve the dispersion efficiency, high-shear pre-dispersion process utilizing the mechanism of dry particle coating was firstly applied to CNTs and 6061Al powder mixtures for a few minutes to de-agglomerate CNTs and uniformly coat them onto surface of 6061Al powder. It was demonstrated that, for the pre-dispersed powders, more rapid and uniform dispersion of CNTs was achieved during following shift-speed ball milling process, which in turn protected CNTs from additional damage and led to better interfacial bonding and higher reinforcing efficiency. As results, compared to counterpart without pre-dispersion, the as-extruded bulk 1.5 wt% CNT/6061Al composites exhibited simultaneous enhancement in Young's modulus, tensile strength and ductility.

Balanced strength and ductility in CNT/Al composites achieved by flake powder metallurgy via shift-speed ball milling

Flake powder metallurgy via shift-speed ball milling (SSBM) was proposed to combine the mechanisms of low-speed and high-speed ball milling (LSBM and HSBM) for carbon nanotube (CNT)-reinforced, strong and ductile aluminum composites. LSBM featured mild ball-to-powder collision and slow flattening of spherical Al powders into flakes, leaving enough time for CNTs to be uniformly dispersed on the surface of Al flakes and causing little damage to CNTs; HSBM featured much stronger collision and cold welding of Al flakes, leading to clustered CNTs within the welded Al particles with serious damage but better inter-flake bonding. Therefore, the coordination of CNT dispersion, integrity and interfacial bonding could be achieved by a smart powder processing of SSBM, namely a longer starting LSBM and a shorter following HSBM. As demonstrated, such SSBM resulted in comparable strength in 1.5wt.% CNT/Al composites but doubled and tripled ductility as those fabricated via LSBM and HSBM.