Large Number Of Nucleation Sites Research Articles

Deformation mechanism and hardening behavior of gradient heterostructured magnesium alloys prepared by severe shear deformation

Lightweight equipment in aerospace and other fields urgently requires magnesium (Mg) alloys components with high-strength plasticity. For this reason, in this study, a gradient heterogeneous structure containing nanocrystallines was constructed successfully using a severe shear deformation process that combines severe plastic deformation techniques and torsional deformation characteristics. The evolution of the microstructure and hardness of Mg-12.12Gd-4.2Y-2.28Zn-0.36Zr (wt%) alloys prepared by severe shear deformation with changes in deformation temperature were investigated. The gradient heterogeneous structure of the alloys formed naturally under high hydrostatic pressure and severe shear stress, and its thickness increased with the deformation temperature. With the application of shear stress, a large amount of rotational dynamic recrystallization (RDRX) behavior occurs in the alloys, refining the coarse initial grains (∼126.3 µm) into fine grains (∼2.03 µm) or even ultrafine grains (∼1 µm). During the RDRX process, low angle grain boundaries (LAGBs) began to form at high distorted grain boundaries and unique lamellar structures, followed by a rapid expansion into the interior of the grains, which ultimately results in the grains being completely covered by subgrains. Meanwhile, the continuously broken long-period stacking-ordered (LPSO) phase and the precipitated bright rare earth rich (RE-rich) phase provide a large number of nucleation sites, further promoting the refinement process of the grains. Subsequently, the grains were further refined to nanocrystallines through the formation and rotation of subgrains under continuous loading of stress. The massive formation of nano-precipitated phases (β phases) along grain boundaries were accompanied by the complete disappearance of other types of second phases. The sources of β phases formation include the layer-by-layer decomposition of the cellular phases and the dissolution/re-precipitation of the LPSO phases. In addition, the introduction of shear stress promotes the random orientation of the DRXed grains through the extensive activation of pyramidal <a> and pyramidal <c+a> slip. The hardness of the alloys gradually decreased as the cumulative strain decreased at different deformation temperature conditions. When the deformation temperature was 440°C, the alloys reached a maximum hardness of 127.67 HV, which was nearly 43.5% higher than homogenized alloys. The ultra-high hardness of the alloys prepared by severe shear deformation is mainly attributed to grain boundary hardening, diffusion hardening and hetero-deformation induced (HDI) hardening.

Acoustofluidics-assisted strategy of zinc oxide nanoarrays for enhancement of phase-change chip cooling

Enhancing flow boiling in microchannel via surface modification is crucial for addressing the energy consumption challenges posed by high-power compact electronic devices. However, improving boiling heat transfer performance with well-defined nanostructured surfaces in a limited space remains a challenge. Herein, we present a simple and straightforward acoustofluidics strategy for stable, controllable, and efficient fabricates of functional Zinc oxide (ZnO) nanoarray silicon chip surface with excellent phase change cooling performance. The intentionally designed flower-like sharp-edge structure integrated acoustic has been experimentally and numerically verified for its enhanced mass transfer mixing. The resulting ZnO nanoarray-coated chip with customizable lengths, densities, and morphology is implemented by simple reactor parameter adjustment. Excellent boiling heat transfer performance is obtained on this surface, giving priority to nucleation (superheat≈ 4 °C), low energy consumption (≤3.2 kPa) and simultaneously enhancing the critical heat flux (CHF) and heat-transfer coefficient (HTC) by up to 70.8 % and 107.5 %, respectively, compared with a smooth chip surface. In situ observation and analysis of the wicking of the nanoarray and nucleation, growth, and departure of the bubbles reflect that ZnO nanoarray promotes the phase change heat exchange process by the large number of nucleation sites and ultrafast liquid re-wetting. These findings not only provide important guidelines for the precise control and rational design of functional nanomaterials, but also provide new insights for embedded cooling and significant energy savings on power devices.

Transformation of a new polyoxometalate into multi-metal active sites on ZIF-derived carbon nanotubes as bifunctional cathode catalyst and dendrite-free anode coating for Zn-air batteries

To improve the kinetics of the ORR/OER at the cathode and inhibit dendrite formation on the anode of a Zn-Air battery (ZAB), a new polyoxometalate (POM) with a basic structrual unit of [Zn{P4Mo6}2] was designed and converted to well-separated Zn/Mo2C catalytic sites on Co, N doped carbon nanotubes (Co-NCNTs) derived from ZIF-67. This conversion was achieved at a relatively low pyrolysis temperature of 600 °C, which circumvented the collapse of catalyst structures, burial of catalytic sites and volatilization of metals. The experimental results demonstrate that the pyrolysis of [Zn{P4Mo6}2] can etch Co-NCNTs-800 to produce a porous structure with an enlarged specific surface area, thus increasing the number of catalytic sites and promoting the transfer of electrons/ions. The high-valence Mo atoms from the POM precursor are inclined to hybridize with O active intermediates produced during ORR/OER, which can improve electron exchange and the ORR/OER performance. Furthermore, the multi-catalytic sites (Zn and Mo2C, etc.) produced from the [Zn{P4Mo6}2] precursor can not only facilitate ORR/OER at the battery cathode, but also inhibit the formation of zinc dendrites by forming a large number of nucleation sites on the battery anode. Accordingly, the ZABs assembled with the POM-derived catalyst exhibit a high open circuit voltage of 1.506 V and a peak power density of 223.54 mW cm−2. Moreover, the assembled all-solid coin cell ZABs also display high capacity and long-term charge–discharge stability. Furthermore, density functional theory calculations demonstrate that the synergy between Zn/Mo2C and Co-NCNTs active sites mainly contributes to the superior ORR/OER catalytic performance.

Pool boiling heat transfer enhancement on the hybrid surfaces coupling capillary wick and minichannels

Pool boiling heat transfer can fully utilize the latent heat of the vaporization, to meet the heat dissipation needs of high-power electronic components. In this study, several enhanced hybrid surfaces were designed and processed by sintering spherical copper powder on the minichannels in different ways. The coupled effects of various parameters of capillary wick and minichannels were considered to enhance the pool boiling heat transfer performance of these hybrid surfaces using HFE-7100 as the working fluid. The bubble dynamic behaviors were captured and analyzed by the high-speed camera. The results indicate that the ring groove around the minichannels and the capillary wick have a significant impact on the boiling heat transfer of these hybrid surfaces. This is because the capillary wick provide a large number of nucleation sites and large specific surface area, which can greatly reduce the contact thermal resistance between the capillary wick and the minichannels. At ΔTsub = 30 K, the critical heat flux (CHF) of hybrid surfaces coupling capillary wick and minichannels is up to 147.4 W/cm2, and its maximum heat transfer coefficient (HTC) is 2.69 W/(cm2·K). Compared with minichannels without capillary wick covered, the CHF and HTC are increase by 86.8% and 192.0%, respectively. Furthermore, a correlation for predicting CHF on these hybrid surfaces covered capillary-wick is proposed. Dimensionless parameters such as the subcooled Jakob coefficient (Jasub), the outer surface area enhancement ratio (AER), the particle distribution coefficient (PDC) and the ratio of inner to outer surface area of capillary wick (IOR) are defined to estimate the effect of different factors on the CHF.

Impact of Rice Husk Ash on the Mechanical Characteristics and Freeze–Thaw Resistance of Recycled Aggregate Concrete

With the accelerating growth of infrastructure construction, carbon emission and environmental pollution problems have become increasingly severe. In order to promote the sustainable development of the construction industry, using rice husk ash (RHA) in recycled aggregate concrete has aroused extensive interest. This study aims to investigate the impact of the partial replacement (0%, 10%, 20%, 30% of binder) of ordinary Portland cement (OPC) with RHA by equal mass on recycled concrete’s mechanical characteristics and freeze–thaw resistance. The workability, compressive strength, mass loss and dynamic elastic modulus of recycled concrete were tested, and the hydration products and microstructure were analyzed using scanning electron microscope (SEM) tests. The mechanism of the freeze–thaw damage deterioration of RHA recycled aggregate concrete was revealed. The results indicate that the incorporation of RHA has an adverse effect on the workability of fresh concrete. Its high specific surface area will provide a large number of nucleation sites for the hydration reaction, refining the pore structure in the paste and improving the weak bonding of the interfacial transition zone (ITZ) by enhancing the matrix’s pozzolanic reaction effect and filling effect, thus improving the compressive strength of concrete. Furthermore, the porous structure of the recycled aggregate attached mortar and mesoporous RHA will absorb a lot of water during the freeze–thaw cycles. With the continuous accumulation of expansion pressure, the interior pores and cracks will gradually expand and extend, leading to more severe damage to the concrete, and the degree of freeze–thaw damage deterioration grows as the RHA replacement ratios increase.

Multifunctional hybrid interface enables controllable zinc deposition for aqueous Zn-ion batteries

Aqueous Zn-ion batteries have gradually become a suitable choice for large-scale energy storage systems owing to their safety and lower cost. However, Zn metal anodes typically suffer from uneven electrodeposition and zinc dendrite formation, which restricts Zn-ion batteries from being used in further applications. To mitigate this problem, a simple and quick chemical surface modification is employed to construct a multifunctional hybrid interface consisting of ZnF2 and Sn on the surface of the Zn metal anode. ZnF2 show a low diffusion energy barrier for Zn2+, effectively shield the direct corrosive reaction from the aqueous electrolyte, and simultaneously increase the hydrogen evolution potential of the Zn electrode. Furthermore, the Sn particles provide a large number of nucleation sites and charge centers, avoiding the direct growth of dendrites. The interface-modified Zn anode achieve stable cycles of 700 h and 500 h at high current densities of 5 and 10 mA/cm2, respectively, while the assembled Zn@ZnF2–Sn||V2O5 full battery achieve over 400 stable cycles at 1 A/g. This work uncover the internal mechanism of inhibiting Zn dendrites by the multifunctional interface, providing a means for stabilizing the Zn anode under practical conditions.

Experimental investigation on mechanical behavior of sands treated by enzyme-induced calcium carbonate precipitation with assistance of sisal-fiber nucleation

Sisal fibers had obvious advantages of mechanical strength on reinforced enzyme-induced calcium carbonate precipitation (EICP)-cemented loose sands. However, there are few related researches, whose research on strength and toughness is not sufficient, and the analysis on mechanism is lacking. In this article, sisal fiber was used to strengthen EICP-treated sand, and the mechanical properties and underlying mechanism were experimentally explored. The results show that the strength and toughness of EICP-treated sand can be effectively improved by sisal fibers. The optimal sisal fiber length is 10 mm and the optimal fiber content is 0.2%. The wet-dry cycle resistance of the samples is improved simultaneously. Microscopic study showed that the rough surface of sisal fiber provided a large number of nucleation sites for calcium carbonate precipitation and formed an effective “bridge network.” This study reports the potential and the underlying mechanism of sisal fiber on improvement of EICP performance by new test methods and provides new insight into enhancing mechanical behavior of EICP-cemented loose sands with natural fiber.

Shape memory and underwater superelastic mof@cellulose aerogels for rapid and large-capacity adsorption of metal ions

Cellulose aerogels have been used in widespread areas, such as absorbents, thermal insulation material and medical material. Herein, we propose an effective strategy to fabricate elastic cellulose aerogels by combining cellulose nanofibers with polyvinyl alcohol (PVA) “glue”. The CA not only had a robust chemical-bond cross-link network, but also had a strong H-bond, which enhanced underwater mechanical properties. Moreover, the compressible CA provided a large number of nucleation sites for the growth of Metal–organic framework nanoparticles (ZIF-67 and ZIF-8) through interface self-assemble. The obtained aerogels with a low density of 9.8–11.2 mg cm−3 and highly porous of 99.4–99.5% possessed excellent elasticity both in air and underwater. The adsorption capacities of the MOF@CA for Pb2+ and Cu2+ are up to 123 mg g−1 and 70.53 mg g−1, respectively. The novel MOF@CA adsorbents with excellent mechanical properties display application prospects in the removal of heavy metals from wastewater.

Formation mechanism of CuNiAl-rich multi-structured precipitation and its effect on mechanical properties for ultra-high strength low carbon steel obtained via direct quenching and tempering process

Ultra-high low carbon baintic steel strengthened by CuNiAl-rich multistructured particles was studied in this work. The influence of direct quenching and tempering (DQ-T) process on microstructural transformation and precipitation behavior of CuNiAl-rich particles were investigated. The high-density dislocations formed in DQ process provide a large number of nucleation sites for the CuNiAl-rich particles. According to the results of phase field method simulation, the coarsening mechanisms of CuNiAl-rich particles included merger mechanism and Ostwald maturation mechanism. The formation of 9R–B2 core-shell structural CuNiAl-rich particles was owing to the inverse concentration gradient diffusion of Cu between particles with different Cu content. The yield strength was 1228 MPa, because of the co-precipitation of 9R–B2 core-shell structural particles with ∼12.5 nm and B2-ordered particles with ∼3.4 nm. The impact absorbed energy was 44.2J at −40 °C. The small grain size contervailed for toughness reduction from co-precipitation.

Flow Pattern Analysis and Heat Transfer Characteristics During Subcooled Flow Boiling in a Rectangular Microchannel on ZnO Microrod Surface

Abstract The combination of microstructured surface and microchannel flow boiling is expected to solve the thermal management problems of high-heat-flux devices. In this study, the experimental investigation of subcooled flow boiling in a high aspect ratio, one-sided heating rectangular microchannel was conducted with de-ionized water as the working fluid. ZnO microrods were synthesized on the titanium surface to be used as the heated surface compared with the bare titanium surface. A facile image tool is utilized to process the flow patterns photographed by a high-speed camera, which is analyzed with the heat transfer characteristics. The flow pattern of isolated bubbly flow reveals the large number of nucleation sites formed on the microrod surface but the heat transfer performance deteriorates with increasing mass flux because of the smaller bubble area and weaker nucleation. With increasing heat flux, the flow pattern changes from isolated bubbly flow to alternating bubbly/slug flow and alternating slug/annular flow. The latter flow pattern is confirmed to bring a higher heat transfer coefficient due to the larger area of thin-film evaporation. Compared with the bare surface, a higher heat transfer coefficient is achieved on the ZnO microrod surface for up to 37% due to the more nucleate sites and strengthened convective evaporation. Therefore, this surface might be suitable for heat dissipation in the watercraft or aerospace industry considering the low density, strong intensity, and corrosion resistance of titanium.

Microstructures and mechanical properties of Nb nanoparticles modified Ni60 hard-facing alloy fabricated by laser metal deposition

Crack-free samples were made from Nb nanoparticles modified Ni60 hard-facing alloy using laser metal deposition. Addition of Nb nanoparticles was carried out to modify the columnar dendrites and eutectic microstructures by providing large number of nucleation sites. The purpose of this study was to evaluate the effect of nanoparticles addition on cracking susceptibility of Ni–Cr–B–Si alloy. The results show that with addition of Nb nanoparticles, the cracking susceptibility reduced significantly with acceptable hardness loss. Large hard phases were refined and the columnar dendrites were converted to equiaxed grains, leading to a separated eutectic microstructure which restrain the initiation and growth of cracks. The study demonstrated a new method to tackle the cracking problem of laser manufactured Ni–Cr–B–Si alloys, accelerating the adoption of Ni–Cr–B–Si alloys on additive manufacturing applications.

Polypropylene/thermoplastic polyester elastomer blend: Crystallization properties, rheological behavior, and foaming performance

AbstractThe inherently linear polypropylene suffers unsatisfying foaming behavior due to its low melt strength. To overcome this drawback, polypropylene‐/polypropylene‐grafted glycidyl methacrylate/thermoplastic polyester elastomer (PP/PP‐g‐GMA/TPEE) blending foam is prepared by the chemical foaming method in this study. The foaming mechanism of blending was studied from the aspects of the rheological behavior and the crystallization property. The results show that TPEE disperses in the PP matrix with fine particles and forms ideal interfaces, which provide a large number of nucleation sites for the foaming process of blending, inducing heterogeneous nucleation. Both of the 15 wt% and 20 wt% TPEE‐modified PP composites show higher shear viscosity and obvious strain hardening behavior. It has been proved that the cross‐linking network structure formed by TPEE and PP‐g‐GMA reaction improves the melt strength. The cell size decreases from 37.6 to 24.8 μm, and the cell density increases from 2.9 × 106 cells/cm3to 2.5 × 107 cells/cm3. Compared with PP composites, the foaming window of the PP/PP‐g‐GMA/TPEE composites was widened.

Effect of Strain on Strain‐Induced Precipitation Behavior of MnS in 3% Si Steel

Hot compression tests of 3% Si steel with a true strain range of 0.02–0.92 at a strain rate of 1 s−1 and a temperature of 1173 K, based on the Gleeble‐1500 thermo–mechanical simulator, are conducted. The effect of strain on the strain‐induced precipitation behavior of MnS is investigated via cold field‐emission ultrahigh resolution scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The experimental results obtained indicate that the volume density of MnS precipitates increases, whereas the mean diameter of MnS precipitates decreases with the increase in strain during the transient deformation stage. However, during the steady deformation stage, these parameters remain nearly constant. The precipitation behavior of MnS during the transient deformation stage is attributed to the increase in dislocation density with the increase in strain. More dislocations create a larger number of nucleation sites, which, in turn, increase the nucleation rate. At the same time, a model about static recovery affecting the dislocation density in the matrix after deformation is also proposed to elucidate the mechanism of the evolution of MnS in the aging process.

Characteristics of carbide-free medium-carbon bainitic steels in high-stress abrasive wear conditions

This study encompasses a comprehensive account of the abrasive wear properties of carbide-free, ultrahigh-strength bainitic steels processed through ausforming at three different temperatures well below the recrystallization stop temperature followed by bainitic transformation at temperatures close to the Ms temperature. Five medium-carbon, high-silicon compositions were designed for the study by suitably varying the alloying levels of carbon, vanadium, niobium, molybdenum, and aluminum. While ausforming at lower temperatures enabled a large number of nucleation sites leading to significant refinement of bainitic laths, the decomposition of austenite at relatively low transformation temperatures was accelerated due to the presence of a high dislocation density, thus enabling completion of bainitic transformation in a reasonable length of time. The steels were characterized in respect of microstructural features and mechanical properties, besides evaluation of wear resistance through a high-stress abrasive wear testing method with natural granite abrasives. The microstructures comprised different fractions of bainitic ferrite and/or granular bainite (56–68%), martensite (0–25%), besides a significant fraction of retained austenite (20–34%) manifesting as pools and also interlath films, depending on the ausforming conditions and subsequent cooling paths. A tensile strength of 1900 MPa level was achieved with hardness exceeding 500 HV for the medium-temperature ausformed steel containing a high carbon content that also showed lowest mass loss in the wear test. The hardness-to-mass loss ratio appeared highly promising with some of the carbide-free bainitic steels on par with or better than the reference martensitic steel. The high work-hardening capability as a consequence of the strain-induced austenite to martensite transformation was considered as the main factor for the superior abrasive wear resistance of the carbide-free bainitic steels.

Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase

The effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. The average grain sizes, fractions of dynamically recrystallized (DRXed) grains, and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller, higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. This was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. The constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in magnesium. Compared with the cast alloys, the onset of the power law breakdown (PLB) occurred at larger Zener-Holloman (Z) parameter values in the extruded alloys. This was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. The flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. This agreed with the microstructural observations.

Preparation of functionalized cellulose nanoparticles and their effect on the crystallization behaviors of poly(l‐lactide) based nanocomposites

AbstractA rather low crystallization rate has greatly limited the application of poly(l‐lactide) (PLLA) in many fields. Thus, functionalized cellulose nanoparticles (CPNs) were prepared based on cellulose aerogel through a novel and simple approach and were then applied as biobased nucleating agents to improve the crystallization rate of PLLA. First, isolated individual CPNs with a mean diameter around 37.2 nm and regular circular shape were obtained. Subsequently, PLLA based nanocomposites with various contents of CPNs were prepared by solution blending. As a result, CPNs promoted the crystallization rate of PLLA significantly. Compared with that of neat PLLA, the crystallinity (Xc) of the nanocomposites increased dramatically more than 30 times to 36.65% at a CPN loading of 0.5 wt%, and the half‐crystal time (t1/2) at 130 °C decreased by about 91%. Furthermore, due to the presence of CPNs, which provided a large number of nucleation sites in the PLLA matrix, the chain conformational and crystallization kinetics behavior of the PLLA based nanocomposites during isothermal crystallization were changed in the early stages, and based on this result a proposal for the nucleation process for CPNs in a PLLA matrix is presented. © 2018 Society of Chemical Industry

Experimental study of pool boiling heat transfer on copper surfaces with Cu-Al2O3 nanocomposite coatings

The current growth in nanoscience created a deep space of research for modern technology in the field of energy conservation by reducing the energy dissipation from the energy conversion applications. The boiling heat transfer enhancement is an important and advanced field of research to increase the performance of energy conversion applications. The pool boiling heat transfer performance of saturated DI water at atmospheric pressure is examined experimentally on copper surfaces with Cu-Al2O3 nanocomposite coatings, as these particles have higher thermal conductivity. The nanocomposite coatings are developed by a single-step electrochemical deposition technique. This technique provides an easy control on surface properties like porosity and coating thickness. The deposition method is studied carefully and responsible surface morphology parameters are reported. The boiling heat transfer coefficient (BHTC) and critical heat flux (CHF) are improved considerably for nanocomposite coatings. The maximum critical heat flux of 1852 kW/m2 and heat transfer coefficient of 199 kW/m2 K are found to be 72.5% and 273% higher than that of bare surface, respectively. The mechanism for pool boiling heat transfer enhancement with Cu-Al2O3 nanocomposite coated surfaces engages several effects like improvement in surface roughness, activation of larger number of nucleation sites, increase in porosity, and improved surface wettability.

Morphology Control of Nanocrystallized C60 Thin Films Prepared by Poor Solvent Immersion

Nanocrystallized C60 thin films of such as hexagonal, plate-like, and rod-like morphologies were recrystallized by poor solvent immersion, employing 1-propanol, 2-propanol, and butanol respectively. A C60 thin film fabricated by evaporation was immersed in the poor solvent, partially dissolving the surface C60. This was followed by the solvent rapidly reaching a supersaturated state, resulting in the induced recrystallization of the C60. C60 fine high-density crystals were successfully prepared using propanol, with crystal sizes varying between 84 and 141 nm by changing the immersion time. In addition, due to the 1-propanol recrystallizing solvated crystals which were formed through interactions between the solvent and the C60, uniform C60 fine crystals were obtained by the formation of a large number of nucleation sites.

Comparison of pool boiling CHF of a polished copper block and carbon steel block on a declined slope

ABSTRACT This study conducts a critical heat flux (CHF) experiment on a carbon steel block, and the block is positioned on slope that is declined at angles of 5° and 10°. The results of the carbon steel block experiment were then analyzed and compared with the results obtained from a copper block experiment that had been conducted previously at the same test facility. The comparison showed that several different types of phenomena had occurred, and the carbon steel block CHF at both 5° and 10° was much lower than that of the copper block. Detailed images of the heating surface of each material were acquired by a high-speed camera under different heat fluxes and analyzed. The carbon steel block surface generates more bubbles compared to the copper block under the same heat flux, which indicates that the carbon steel block should have a large number of nucleation sites. This causes a higher CHF. Finally, several existing theories on CHF mechanisms were also analyzed in an attempt to explain the difference of copper and carbon steel. It seemed that the contact angle alone was not sufficient to explain the large CHF decrease in the carbon steel block.

Control of the microstructure and mechanical properties of electrodeposited graphene/Ni composite

Nickel composites reinforced with reduced graphene oxide (rGO) nanosheets were fabricated by a direct current electrodeposition technique. The low volume fraction of graphene can promote the cathodic polarized potential, facilitate the transport of ions and electrons on electrodes, and provide a large number of nucleation sites, consequently accelerate the formation of heterogeneous microstructure features. The graphene/Ni composite with 2 mL graphene dispersions demonstrates a tensile strength of 864 MPa and a plastic elongation of 20.6%, which are 25% and 36% higher than that of the pure bulk Ni. The enhancements in strength and ductility of the composite can be ascribed to the bimodal microstructure, for which the fine grain population provides for enhanced strength, whereas the coarse grain population enhances ductility by enabling strain hardening. On the contrary, the positive role of rGO in microstructure control will be weakened due to the agglomeration of rGO sheets in a high-volume plating bath. The low adsorption quantity of rGO is unfavourable for the nucleation of Ni matrix, accordingly produces a uniform fine-grained microstructure. The tensile strength of the composite with 5 mL rGO is 750 MPa, whereas the fracture elongation is only 7.5%. It is believed that a proper addition of rGO dispersion makes a promising microstructure for advanced graphene/Ni composite.