Cu6Sn5 Phase Research Articles

Co, In, and Co–In alloyed Cu6Sn5 interconnects: Microstructural and mechanical characteristics

The mechanical reliability of the future miniaturized interconnects is mainly governed by the intermetallic compounds such as Cu6Sn5. Alloyed Cu6Sn5 with various elements, including Co and In, have been introduced and attracted attention for different reasons, such as the enhancing mechanical reliability and lowering the bonding temperature. Hence, this work aimed to evaluate the microstructural and mechanical properties of Cu6Sn5-, Cu6(Sn,In)5-, (Cu,Co)6Sn5-, and (Cu,Co)6(Sn,In)5-interconnects. The grain size, grain orientation, and crystal structure of the pure and alloyed Cu6Sn5 phases were analyzed using electron backscatter diffraction. The results revealed that all the joints contained monoclinic and hexagonal crystal structures arbitrarily formed across the bond-line. Furthermore, the Cu6Sn5 grains exhibited random grain orientation and there was no discernible difference between the pure and alloyed Cu6Sn5 interconnects other than Cu6(Sn,In)5 grains elongated along the perpendicular direction to the bonding interface. However, it was found that alloying elements altered the grain sizes. In alloying refined and elongated the Cu6Sn5 grains while the Co alloying enlarged the Cu6Sn5 grains. The mechanical properties of the interconnects were examined using nanoindentation test. The results indicated that the hardness (H) and Young's modulus (Ei) values of Cu6Sn5 is increased with the alloying elements. (Cu,Co)6(Sn,In)5 showed the highest Ei/H value which indicates its highest plasticity.

Effect of deposition potential on electrodeposition of Sn-Ag-Cu ternary alloy solderable coating in deep eutectic solvent

Ternary Sn-Ag-Cu solderable alloy coatings were electrodeposited using deep eutectic solvent-based electrolytes, at different deposition potentials. The obtained deposits have been characterized from surface morphology, composition, crystalline grain and phase via Scanning Electron Microscopy (SEM) associated with Energy Dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). To get information on the alloy melting point, Differential Scanning Calorimetry (DSC) has been involved.The results showed that the crystalline grain became finer and the coating became denser as the deposition potential increased. In addition, the presence of Cu6Sn5 phase is facilitated by more cathodic deposition potentials while the Ag3Sn phase was evidenced at lower potential values. The value of the melting point of Sn-Ag-Cu alloy (Sn90.9-Ag7.6-Cu1.5) deposited at potentials of −1.2 V was of 215.02 ℃. Based on the results obtained during the analysis of the current–time curves using the Scharifker-Hills' model, it has been found that both single metal and alloy deposition processes correspond to a nucleation and tridimensional growth controlled by diffusion. The deposition processes of Sn and Ag are conducted by an instantaneous mechanism, while in the case of Cu, a progressive one has been determined. The deposition process of Sn-Ag-Cu alloy showed a deviation from the instantaneous nucleation.

Effect of Nanosized Ni Reinforcements on the Structure of the Sn-3.0Ag-0.5Cu Alloy in Liquid and After-Reflow Solid States

The Sn-Ag-Cu (SAC) alloy family is commonly used in lead-free solders employed in the electronics industry, for instance, SAC305, SAC387, SAC405, etc. However, the trend in manufacturing small electronic products and device miniaturization faces some disadvantages in terms of mechanical properties and their higher melting temperatures compared to Pb-Sn solders, prompting new research relating to the reinforcement of existing SAC solders. The current study presents structural features of nanocomposite (Sn-3.0Ag-0.5Cu)100−x(nanoNi)x solders with 0.5 wt.%, 1.0 wt.%, and 2.0 wt.% Ni. Structural analysis of the investigated samples were performed by means of X-ray diffraction in a liquid state and scanning electron microscopy (SEM). SEM showed the mutual substitution of Ni and Cu atoms in the Cu6Sn5 and Ni3Sn4 phases, respectively. The performed structural studies in liquid and solid states provided essential information concerning the structural transformations of liquid Sn-3.0Ag-0.5Cu alloys caused by minor additions of nanosized Ni powder. The melting point and degree of undercooling of the samples were investigated by DTA analysis.

Effect of Pb on microstructure and mechanical properties of Tin Babbitt alloy

This paper mainly studies the microstructure and properties of babbitt alloys, and analyzed the influence of lead on the microstructure and properties of the alloys by adding alloying element Pb, The results show as follows:with the increase of Pb content, the hardness of ZSnSb11Cu6 alloy first increases and then decreases. The maximum at 0.75% is 26.96HB. The tensile strength and elongation showed a trend of rising, then falling and then rising, and the mechanical properties were relatively high at 0.35%.The addition of Pb changes the morphology of Cu6Sn5 phase. With the increase of lead content, the β phase decreases and then grows, and the needle-like η phase dendrite grows.

Efficient Cu2ZnSnSe4 thin film solar cells prepared from an ethanolamine-dimethyl formamide based sulfur/selenium-free solution

Most reported solution processed Cu2ZnSn(S,Se)4 thin film solar cells are fabricated from precursor solution with sulfur source. However, the use of sulfur-containing solution is undesirable from the viewpoint of environment and security due to the release of sulfur-containing harmful gases when drying precursors. Here, a novel sulfur/selenium-free solution method using ethanolamine-dimethyl formamide as solvent was developed for the preparation of Cu2ZnSnSe4 thin films. It was found that Cu-Sn alloy phases were formed in precursor during drying process. The formation and phase transition mechanisms of the Cu-Sn phases were illustrated. The aggregation level of the alloy phases and their distribution in the precursor depend on the drying time. Effects of different drying time on structural, morphological and photoelectric properties of the resulted Cu2ZnSnSe4 films were systematically investigated. The Cu2ZnSnSe4 absorbers exhibit a sandwiched structure or a four-layer structure, which is determined by the drying time of precursor, implying two different grain growth mechanisms. The devices with drying time of 6 min show larger grain size, longer carrier life time, higher external quantum efficiency and better average photovoltaic performance.

Extraction of precious metals by synergetic smelting of spent automotive catalysts and waste printed circuit boards

Spent automotive catalysts (SACs) and waste printed circuit boards (WPCBs) are the most important secondary resource containing precious metals (PMs). A resource-saving process of extracting PMs from SACs and WPCBs by synergistic smelting of these two wastes was proposed. The main feature of the process was to use metal components in WPCBs as the collector metal of PMs and use carrier components in SACs as the slag formative. A SiO2-FeO-Al2O3-MgO-CaO slag system was first designed for the synergistic smelting by analyzing phase diagrams and liquid phase formation. On this basis, the laboratory -scale synergistic smelting experiments of these two wastes were carried out. Under the optimal conditions of 1350 °C, FeO/SiO2 mass ratio = 1.0, WPCBs/SACs mass ratio = 0.25, 5 wt% CaO content in the slag, and 3 h smelting time, the extraction efficiencies of Pd, Rh, Ag and Au were 90.5%, 93.2%, 98.9% and 94.5%, respectively. In the collected crude Cu ingot after synergistic smelting, PMs were mainly concentrated in the Cu-Sn phase. Also, a potential industrial system for the synergistic-smelting process based on a top-blown injection smelting furnace was proposed. The novel process will provide an effective way for extracting PMs from secondary resources.

Rapid formation, grain refinement and shear property of high-temperature-stable full IMC joints

Solid liquid interdiffusion (SLID) bonding that can fabricate high-melting point full IMC joints is playing an increasing key role in 3rd-generation semiconductor power electronic device packaging for high temperature applications. In this study, rapid formation of Cu/intermetallic compounds (IMCs)/Cu–8Ni joints with fine (Cu,Ni)6Sn5 and (Cu,Ni)3Sn grains was achieved by SLID bonding Cu/Sn/Cu–8Ni structure. The formation and evolution of the IMCs and the elemental distribution and shear property of the full IMC joints during bonding and subsequent aging were systematically investigated. Due to the Ni doping, the growth of the (Cu,Ni)6Sn5 IMC was significantly accelerated during bonding while that of the Cu3Sn phase was strongly suppressed during both bonding and aging. The total IMC growth rate in the Cu/Sn/Cu–8Ni solder joints was approximately 44 times faster than that in the Cu/Sn/Cu solder joints under the same bonding condition. After aging at 260 °C for up to 400 h, the full IMC joints showed good thermostability composing of fine IMC grains and no Kirkendall voids were observed. The shear strength of the full IMC joints slightly dropped from 63.17 MPa after bonding to 54.35 MPa after aging. The proposed SLID bonding using Cu/Sn/Cu–8Ni structure was proved to be a promising method for forming high-temperature-stable full IMC joints for 3rd-generation semiconductor power device packaging or 3D packaging applications.

Study on Microstructure and Mechanical Properties at Constant Electromigration Temperature of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu Solder Joints

To solve the electromigration problem of micro-electronic connection solder joints, an ideal electromigration tester was designed, and the thickness of the intermetallic compounds (IMCs), average void diameter, grain orientation, failure, shear strength, and fracture path of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu solder joints under constant-temperature electromigration were studied. The results indicate that the solder joints show evidence of typical electromigration polarity in the asymmetric growth of interfacial IMCs on the anode and cathode sides under the conditions of a current density ≥7 × 103 A/cm2 and an included angle between the c-axis of the β-Sn grains and the current direction θ ≤ 53.2°. The anode-side interfacial IMC is dominated by a Cu6Sn5 phase with a gradually increasing thickness, forming a Cu3Sn phase and showing evidence of microcracks. The Cu6Sn5 phase of the cathode-side interfacial IMC is gradually completely dissolved, and the growth of the Cu3Sn phase is accompanied by the formation of Kirkendall voids. The anisotropic diffusion of Cu atoms in the β-Sn of the micro-solder joints causes increased solder joint resistance and reduced shear strength. The shear fracture path of the solder joints moves from the cathode side near the IMC solder seam to the Cu3Sn interface. The shear fracture mechanism changes from ductile transgranular fracture dominated by β-Sn dimples to brittle fracture dominated by interfacial IMC cleavage and slip steps.

Effect of alloying elements on mechanical behaviour of Cu-Zn-Sn bronzes

Abstract The effect of Fe, P and Mn on microstructure and fatigue properties of CuZnSn bronzes investigated with optical microscopy and scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, hardness, tensile and fatigue tests. The addition of Fe, Mn and P to Cu-Zn-Sn bronzes formed Cu31Sn8, Cu6Sn5, ZnSn2, PbSnS2, ZnS, Cu2S, FeZn9 and FeZn21 phases. These phases were deposited between the dendrite arms and were dissolved in the matrix in small amounts. Especially, these precipitated phases were effective in fatigue properties. The formation of Cu-Sn, Cu-Zn and Zn-Sn intermetallic phases emitted due to the addition of Fe, Mn and P increased the fatigue strength. The spread of ferrous phases caused an increase in mechanical properties. The beneficial effect of P addition on the fatigue life far surpassed that of Mn and Fe additives.

Failure Analysis of Printed Circuit Board Solder Joint under Thermal Shock

Investigating the failure mechanism of solder joints under different temperature conditions is significant to ensure the service life of a printed circuit board (PCB). In this research, the stress and strain distribution of a PCB solder joint was evaluated by high- and low-temperature thermal shock tests. The cross-section of the solder joint after thermal shock testing was measured using a 3D stereoscopic microscope and SEM equipped with EDS. The microstructure of the lead-free solder joint and the phase of the intermetallic compound (IMC) layer were studied by XRD. The working state of the PCB solder joint under thermal shock was simulated and analyzed by the finite element method. The results show that thermal shock has a great effect on the reliability of solder joints. The location of the actual crack is consistent with the maximum stress–strain concentration area of the simulated solder joint. The brittle Cu6Sn5 and Cu3Sn phases at the interface accelerate the failure of solder joints. Limiting the growth of Cu6Sn5 and Cu3Sn phases can improve the reliability of solder joints to a certain extent.

Microstructural, thermal and mechanical properties of Co added Sn–0.7Cu lead-free solder alloy

This study investigated the effects of cobalt microalloying addition on the microstructural features, thermal characteristics and mechanical behavior of eutectic Sn–0.7wt%Cu lead-free solder alloys. The results show that minor cobalt addition of ~ 0.05 wt% causes significant grain refinement of β-Sn, facilitates the formation of fine fibers (Cu,Co)6Sn5 phases and preventing the formation of η′-Cu6Sn5 phases, whereas a large amount of Co (~ 0.5 wt%) additions accumulated in the (Cu,Co)6Sn5 IMCs and clearly changed into coarse fibers. The precipitation strengthening mechanisms of fine fibers (Cu,Co)6Sn5 in the β-Sn matrix increased the ultimate tensile strength (UTS) and Young’s modulus (Y) of the alloy from 30.5 MPa and 15 GPa to 44.6 MPa and 22.3 GPa, respectively, but the ductility decreased from 60 to 45.7%. The coarse fibers (Cu,Co)6Sn5 in eutectic alloys is of interest from not only increased UTS and Y to 38.7 MPa and 16.3 GPa but also maintaining the ductility at the same level, allowing for unique microstructure design. Furthermore, 0.05wt% of Co significantly reduce the onset, eutectic temperatures and undercooling, although pasty rang has been slightly raised, which may enhance the thermal characteristics. This presumably has important implications for the reliability of solders as well as their performance in electronic service.

Microstructure and Mechanical Performance of Tin-Based Babbitt Alloy Containing Iron Oxide and Silica Nanoparticles

Iron oxide and silica nanoparticles were individually incorporated in tin-based Babbitt alloy and combined to prepare a novel class of nanocomposites for bearing material applications. The route of liquid metallurgy in combination with the stirring technique was adopted to manufacture nanocomposites. Microstructural evolution and mechanical property evaluation were performed by optical and electron microscopy, EDS, hardness, compression, and wear tests. The morphology of the Cu6Sn5 phase was changed from elongated to spherical in the microstructures of nanocomposites. The solitary addition of 0.5 wt% iron oxide nanoparticles improved the hardness and compressive strength but adversely affected the wear properties by increasing the weight loss and friction coefficient value. In contrast, the addition of 0.5 wt% silica nanoparticles could not significantly increase the hardness and compressive strength but it could improve the tribological properties by reducing the weight loss and friction coefficient value. Tin-based Babbitt alloy showed a compressive strength of 89.22 ± 0.50 MPa after the addition of 0.5 wt% iron oxide showing a rise of ~11%. The combined effect of the addition of both types of nanoparticles showed considerable results, i.e., a rise of ~7.9% (86.75 ± 0.68 MPa). The balanced approach of incorporating dual reinforcements of 0.25 wt% iron oxide and 0.25 wt% silica nanoparticles intermediately improved the hardness, compressive strength, and decreased weight loss.

Machine learning search for stable binary Sn alloys with Na, Ca, Cu, Pd, and Ag.

We present our findings of a large-scale screening for new synthesizable materials in five M-Sn binaries, M = Na, Ca, Cu, Pd, and Ag. The focus on these systems was motivated by the known richness of M-Sn properties with potential applications in energy storage, electronics packaging, and superconductivity. For the systematic exploration of the large configuration space, we relied on our recently developed MAISE-NET framework that constructs accurate neural network interatomic potentials and utilizes them to accelerate ab initio global structure searches. The scan of over two million candidate phases at a fraction of the typical ab initio calculation cost has uncovered 29 possible intermetallics thermodynamically stable at different temperatures and pressures (1 bar and 20 GPa). Notable predictions of ambient-pressure materials include a simple hP6-NaSn2 phase, fcc-based Pd-rich alloys, tI36-PdSn2 with a new prototype, and several high-temperature Sn-rich ground states in the Na-Sn, Cu-Sn, and Ag-Sn systems. Our modeling work also involved ab initio (re)examination of previously observed M-Sn compounds that helped explain the entropy-driven stabilization of known Cu-Sn phases. The study demonstrates the benefits of guiding structure searches with machine learning potentials and significantly expands the number of predicted thermodynamically stable crystalline intermetallics achieved with this strategy so far.

Effect of Sb content on the phase structure and interface structure of Sn1.0Ag0.5Cu lead-free solder

Based on the alloy Sn1.0Ag0.5Cu, Sb powder is added at a certain mass percentage to form the solder alloy Sn1.0Ag0.5CuxSb (x = 0 wt%, 0.5 wt%, 1.5 wt%). The melting point of the solder was determined by differential scanning calorimetry, the alloy interface morphology was observed by scanning electron microscopy, and energy-dispersive X-ray spectroscopy was performed to analyze phase compositions. Thermo-Calc software was used to calculate the variation in phase content, the solidification curve, Gibbs energy, the driving force, liquid/solid phase lines, the phase diagram, and the nucleation radius of Sn1.0Ag0.5CuxSb(wt%). In addition, the calculation results were used to explain the interface growth mechanism. According to the results, the precipitation/transition temperature of each phase and the content of the newly formed phase SnSb gradually increased with the increase in Sb content. After the addition of Sb, both temperatures of the liquid-phase line and the solid-phase line slightly increased, and the calculated values showed the same trend as the measured values. Two heat absorption peaks were observed during the melting process. The Gibbs energy and nucleation radius of the Cu6Sn5 phase increased with the increase in Sb content, indicating that Sb can inhibit the growth of the Cu6Sn5 phase. The addition of Sb rendered the Sn-rich phase denser and finer and reduced the thickness of the intermetallic compound layer and the generation of cracks; these changes intensified with increasing aging time. Comprehensive analysis revealed optimal reliability of the solder for an Sb content of 0.5 wt%.

Experimental investigations of heat generation and microstructure evolution during friction stir processing of SnSbCu alloy

The paper presents the results of experimental investigations of the heat generation and microstructure evolution during the friction stir processing (FSP) of the SnSb11Cu6 alloy. The Triflute tool was used for modification; the process was carried out using two rotational speeds of the tool: 280 and 560 RPM and a constant linear speed of 355 mm/min. Microstructure studies were performed employing the techniques of light microscopy and scanning electron microscopy along with analysis of the chemical composition of micro-areas. Additionally, the phase composition was investigated by means of the X-ray diffraction method, and electron backscatter diffraction (EBSD) analysis and hardness testing were performed before and after FSP modification. Furthermore, measurements of the temperature directly on the modified surface by means of a thermal imaging camera and the temperature in the modified zone with a thermocouple system were performed. It was proved that using FSP to modify the SnSbCu alloy promotes refinement and homogenization of the microstructure, as well as improvement of the hardness. The hardness of the starting material was 24 HB, and after FSP, the hardness increased and amounted to, respectively, 25 and 27 HB after processing at 280 and 560 RPM. The microstructure in the stir zone is formed by the dynamic recrystallization (DRX) process and consists of almost equiaxed tin-rich matrix grains with a size of approx. 5–30 µm and fine particles of Cu6Sn5 and SnSb phases. The temperature distribution in the FSP zone is not uniform and changes in a gradient manner.

Microstructural and mechanical characterization of Cu/Sn SLID bonding utilizing Co as contact metallization layer

Most micro-electro-mechanical systems (MEMS) devices contain fragile moving parts, which poses challenges in process integration of interconnection methods requiring wet-chemistry, such as solid-liquid interdiffusion bonding (SLID). These sensitive MEMS structures can be protected from either the wet-chemistry or plated metals during chemical/electro-chemical plating of SLID interconnection materials; however, this is a complex process. Hence, our previous research has investigated employing a physically deposited contact metallization on the wafers containing functional devices instead of chemically deposited layers (such as electrochemical Cu). Co is a plausible contact metallization layer for Cu-Sn SLID bonding, as it is chemically compatible with Cu–Sn systems. Furthermore, it can positively impact the mechanical reliability of the intermetallic compounds (IMCs) due to the stabilizing of the HT-hexagonal Cu6Sn5 phase down to room temperature and suppressing the Cu3Sn phase formation and subsequent void formation. However, it is critical to control Co thickness to achieve a stable bond based on our previous research on Co bulk in contact with Cu-Sn electroplated silicon chips. To utilize Co as a contact metallization layer for wafer-level Cu-Sn SLID bonding, it is necessary to define appropriate metal layers in the contact metallization stack. Consequently, the present study investigated four different contact metallization stacks including A) 40nmTi/100 nm Co, B) 40 nm Ti/200 nm Mo/100 nm Co, C) 40 nm Ti/500 nm Co, and D) 40 nm Ti/200 nm Mo/500 nm Co. More specifically, we evaluated the microstructural formation and evolution and mechanical performance of the joints. Our study revealed that the Ti/Mo/100 nm Co contact metallization stack for (4 µm)Cu/(2 µm)Sn SLID bonding is composed of IMCs (Cu,2.5at%Co)6Sn5 and Cu3Sn without remaining Sn. Moreover, the joint contained a negligible number of voids even after long-time annealing at 150 °C. Our analysis of the mechanical properties of the joint showed that 1) the tensile fracture surface exhibited a mixture of ductile and brittle fractures, and 2) the Young’s modulus of (Cu,2.5at%Co)6Sn5 was higher than Cu6Sn5, while hardness of (Cu,2.5at%Co)6Sn5 and Cu6Sn5 were comparable. By employing a Ti/Mo/100 nm Co contact metallization stack, the current study was able to produce 25 µm and 10 µm void free (4 µm Cu/2 µm Sn) microbumps.

Effect of indium on microstructure, mechanical properties, phase stability and atomic diffusion of Sn-0.7Cu solder: Experiments and first-principles calculations

Sn-0.7Cu–In ternary alloy solders have received much attention because of their excellent weld stability and wettability. However, how to inhibit or slow down the formation of defects at the welding interface has always been the focus of research. The effects of In on melting point and microstructure of Sn-0.7Cu solders and phase stability and growth rate of intermetallic compounds (IMCs) in the solders were investigated by means of experiments and first-principles calculations. The Rietveld refinement results showed that the lattice constants of β-Sn and η′-Cu6Sn5 (Cu6Sn5) phases increase after In addition. Moreover, In can decrease the melting point, but increase the melting range of Sn-0.7Cu solders. After adding In, the ultimate tensile strength (UTS) increases, while the elongation decreases. From the first-principles calculation results, the stability of Cu6Sn5 increases after In doping, and In doping results in the formation of new chemical bonds between In atom and the neighboring Cu and Sn atoms. Ultimately, the diffusion activation energy and atomic migration barrier of the Cu atom increase after In doping, which in turn decreases the growth rate of Cu6Sn5.

High-temperature effects on kinetics and grain orientation of the Cu41Sn11 phase formed from the full Cu3Sn joint during the aging process

In the present study, the intermetallic compound (IMC) joints consisting of Cu3Sn were aged at high temperatures of 540, 560, and 580 °C to form a sole phase of Cu41Sn11 in a short time period. The variations in morphology, growth kinetics, and grain orientation for the Cu41Sn11 phase originating from the Cu3Sn during the high temperature conditions were systematically investigated. The original Cu3Sn phase appeared as slender grains, while the final phase, which contained Cu41Sn11 grains, was displayed as coarse columnar grains. The growth kinetics for the Cu41Sn11 phase during the 540, 560, and 580 °C temperature testing periods were roughly controlled by the grain boundary diffusion and more precisely controlled by the activation energy, which was 72.86 kJ/mol. The growth rate constant of k0 was 2.5*10^7 μm3/min. The original Cu3Sn phase exhibited two preferred orientations of [100] and [203], while the Cu41Sn11 phase did not exhibit the apparent grain orientation. Various temperatures had specific effects on the kinetics and the orientation: The newly formed Cu41Sn11 grains were used to maintain the coherent or semi-coherent interface ((111)F//(100)P and [101]F//[010]P) and reduce the interfacial energy, which resulted in the step-growth mechanism during the early stage noted at 540 °C (lower temperature); by contrast, non-coherent interface between Cu3Sn and Cu41Sn11 was formed during the higher temperature (580 °C), which also resulted in the formation of more small-size cores with large amounts of grain boundaries without apparent orientation; their mechanism of growth was controlled by the grain boundary diffusion.

Wear behavior of graphite self-lubricating Babbitt alloy composite coating on 20 steel prepared by laser cladding

A tin-based Babbitt self-lubricating composite coating was fabricated on 20 steels substrate by laser cladding through the mixed powders of nickel-plated graphite (Ni-Gr) composite powders and Babbitt alloy powders, aiming at improving wear resistance of Babbitt alloy coating. The results showed that the self-lubricating phase (graphite) coated by the nickel still remained elemental in the composite coating after laser cladding. Both Babbitt coating and Ni-Gr/Babbitt composite coating were uniform and density, without pore, cracks or any other defects, and were mainly composed of α-Sn solid solution phase, Cu6Sn5 and SnSb precipitated phases. The grains were obviously refined for the composite coating due to the heterogeneous nucleation. The nano-hardness (H), nano-hardness/elastic modulus (H/E) and (H3/E2) for the Ni-Gr/Babbitt composite coating were 1.15 GPa, 0.0137 and 1.9 × 10−4, which was much higher than that of the Babbitt coating with the value of 0.57 GPa, 0.0068 and 2.3 × 10−5. With respect to the increase in the nano-hardness, Ni-Gr/Babbitt composite coating also exhibited a low friction coefficient and wear rate with the value of 0.301 and 6.31 × 10−6 mm3/N∙m. The addition of Ni-Gr can effectively improve the self-lubricating and wear behavior of Babbitt alloys.

Encapsulating Sn-Cu alloy particles into carbon nanofibers as improved performance anodes for lithium-ion batteries

The SnCu-SiO2 @CNFs composite nanofibers are successfully fabricated by electrospinning and subsequent heat treatments, in which the Sn-Cu alloy particles are uniformly confined in carbon nanofibers (CNFs) in the presence of SiO2. The characterization results show that incorporating SiO2 into the CNFs matrix can mitigate the problem of the phase separation between Sn-Cu alloy particles and CNFs and increase the fibrous structural integrity of the composite electrodes. Importantly, the SnCu-SiO2 @CNFs-1.0 composite electrode displays the improved electrochemical performance when the amount of Cu(Ac)2 is controlled at 1.0 mmol, in which the discharge specific capacity of the electrode not only delivers 501.8 mAh/g after 100 cycles at 100 mA/g, but also retains 467.4 mAh/g after rate cycles when the current density is abruptly recovered to 100 mA/g. Moreover, the SnCu-SiO2 @CNFs-1.0 electrode can possess an enhanced Li+ diffusion coefficient of approximately 1.58 × 10−16 cm2 s−1 and a high Warburg coefficient of 568.9 Ω cm2 s−0.5 at room temperature. The enhanced electrochemical performance can be partly ascribed to the complete encapsulation of Sn-Cu alloy particles by the CNFs matrix, and partly to the promotion of the over-all electronic conductivity. Furthermore, the flexible and conductive CNFs matrix and the stable Cu6Sn5 phase can conjoinedly accommodate the volume change of the electrodes during charge/discharge processes. Therefore, the facile strategy for encapsulating Sn-Cu alloy particles into CNFs may offer some a prospective instruction for the alloy anodes in the field of energy storage.