Search results

This paper aims to investigate the energy-saving effect and mechanism of serpentine as lubricant additive in the simulated condition.

An ABLT-1 bearing test machine was used for 1,350 hours and an MM-W1 three-pin-on-disk apparatus was used to investigate its anti-friction effect. The worn surface was characterized by scanning electron microscopy equipped with energy dispersive spectroscopy.

The results show that the energy-saving effect was improved after adding serpentine powder in oil and that both the friction coefficient and mass loss were dramatically decreased. The analysis on worn surface layer demonstrates that an auto-reconditioning surface layer was formed on the worn surface, which was responsible for the decrease in friction and wear.

The simulation test for the metal bearing was conducted over 1,350 hours using lubricant with and without serpentine powder. The addition of serpentine powder enhanced the energy-saving rate over time, stabilizing at about 13 per cent after 1,000 hours. An auto-reconditioning surface layer was formed on the surfaces of disassembled bearing lubricated with serpentine doped oil, resulting in dramatic decrease of both the friction coefficient and the mass loss. In addition to normal load and the accumulation of serpentine powder in the furrows and scratches of the deformed layer, the formation of the surface layer was possibly related to the substrate deformation induced by friction force.

The purpose of this paper is to comparatively investigate the microstructure and interfacial intermetallic compound (IMC) layer of Cu/SACPG/Ni and Cu/SAC0307/Ni solder joints after thermal aging.

The specimens were thermally aged at 150°C for 0, 24, 168 and 500 h. The microstructure and morphology of the interface IMC layer were observed by means of scanning electron microscope. The IMCs and the solder bump surface were analyzed by EDS. Moreover, the thickness of IMC layer was measured by using the image analysis software.

The morphology of IMC of Cu/SAC0307/Ni solder joint was consistent with that of the Cu/SACPG/Ni joint, which indicates that the addition of P and Ge had little effect on the IMC formation. The needle-like (Cu,Ni)6Sn5 was formed at the interface of solder/Ni solder joints. Meanwhile, the tiny particles inferred as Ag3Sn phase attached to the surface of (Cu,Ni)6Sn5. The growth rate of IMC layer of the Cu/SACPG/Ni joint was smaller than that of Cu/SAC0307/Ni joint with aging time increasing, which means the addition of trace P and Ge can slightly suppress the diffusion rate of the interfacial IMC.

There are no previous studies on the formation mechanism of the IMC layer of SAC0307 solder alloys with P and Ge addition.

This paper aims to investigate the correlation between wear behavior and microstructure evolution in friction-induced deformation layers (FDL) of 30CrMnSi steel, especially the role of strain-hardening induced by plastic deformation in FDL, which accordingly alters the wear behavior.

Dry sliding friction and wear behaviors of the 30CrMnSi steel against quenched and tempered GCr15 steel were studied using a pin-on-disc tester. The microstructure, hardness and plastic deformation of FDL were investigated.

It was found that the evolution of microstructure and strain-hardening induced by plastic deformation were occurred in the subsurface. When the microstructure, hardness and depth of the plastic deformation layer (PDL) reached a relatively steady state, the friction process transformed into stable-state stage. The wear loss and depth of the PDL was in dynamic equilibrium at stable wear stage.

In this paper, the correlation among the microstructure evolution, the strain-hardening and wear behavior were systemically analyzed. This paper could provide a theoretical reference for optimizing the microstructure and strain hardening properties of tribo-pairs materials.

The purpose of this paper is to put forward the lubrication model of oil bearing and enrich the design theory under the condition of mixed lubrication.

A mixed lubrication model of bilayer porous bearing is established. The effects of the working conditions on the lubrication performance and seepage behavior were analyzed.

Results show that the oil film pressure mainly occurs in the bearing convergence zone and contact pressure mainly occurs near the minimum film thickness. The oil infiltrates into the porous matrix in the contact area and precipitates out to the friction surface at the inlet of the contact area. The oil seepage velocity and dynamic pressure effect at the friction interface can be improved by reasonably matching the load and speed. With the decrease of the external load or increase of the rotating speed, the lubrication performance becomes well.

This study provides a reference for the design and application of oil bearing under harsh working conditions.

Serpentine is usually added into the lubricant oil to form a self-repairing protective layer on worn ferrous surface. But few works have paid close attention to the preparation of composites with the addition of serpentine. In this work, serpentine reinforced Al matrix composites were successfully prepared to be industrial lubrication components. And its fabricating parameters, compressive strength and tribological properties were analyzed.

An MM-W1 three-pin-on-disk apparatus was used to investigate the tribological properties. The worn surface, microstructure and cross-sectional morphologies were characterized by scanning electron microscopy equipped with energy dispersive spectroscopy. The compression test was carried out on a universal testing machine. An X-ray diffractometer was used to investigate the phase constitutions. The decomposition temperature of serpentine powders was investigated by a thermal analyzer, which allows simultaneous differential scanning calorimetry and thermogravimetry. With the help of finite element method model, a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.

Through evaluating density and Brinell hardness, sintering at 560°C for 3 h are the appropriate parameters for fabricating the composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.

Serpentine was added in fabricating the Al matrix composites for the first time. Sintering parameters were optimized to make better Al/Si/serpentine composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient under the dry sliding condition. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. It is hoped to be helpful in further confirming the factors for the formation of the self-repairing surface layer, and in designing a new industrial anti-friction composite used for dry sliding conditions.

The purpose of this study was to comparatively investigate interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu (SAC/Cu) solder joints, and to determine any differences.

The samples were annealed after isothermal ageing at 150°C for 0, 168 and 500 hours, and their cross-sections were observed by scanning electron microscopy and energy dispersive spectroscopy.

The interfacial IMC morphology in two joints had significant differences. For the Cu/SAC/Cu joints, the granular and short rod-like Ag3Sn particles attached on the surface and boundary of interfacial Cu6Sn5 grains were detected, and they coarsened observably with ageing time at 150°C, and lastly embedded at the grain boundaries. However, for the Cu/SACBC/Cu joints, there were tiny filamentous Ag3Sn growing on the surface of interfacial Cu6Sn5 grains, and the Ag3Sn had a tendency to break into nanoparticles, which would be distributed evenly and cover the IMC layer, profiting from the Bi and Cr precipitates from solder matrix during ageing.

The paper implies that the addition of Bi and Cr could affect the IMCs of joints, thereby delaying interfacial reactions between Sn and Cu atoms and improving the service reliability. The SACBC solder is a potential alloy for electronic packaging production.

In a previous study, the authors proposed a new low‐silver solder alloy Sn‐ x(1.0, 1.5, 2.0)Ag‐0.3Cu‐3.0Bi‐0.05Er (wt.%) (SACBE) and the purpose of this paper is to provide additional useful information for new solder alloy development. The growth behaviour of the interfacial IMC layers for Cu/SACBE/Cu and Cu/SAC/Cu joints and their bonding strengths after thermal aging at 150°C for 0, 24, 168 and 500 hours are investigated and the effects of adding elemental Bi and Er on the growth of interfacial IMC layers in the joints, and their tensile properties, are characterized and discussed.

The tensile properties of the Cu/Sn‐3.0Ag‐0.5Cu/Cu (Cu/SAC/Cu) and Cu/SACBE/Cu joints during thermal aging at 150°C for 0, 24, 168 and 500 hours were investigated, respectively. The thickness of interfacial IMC layer and the fracture surface of solder joint after isothermal aging were observed and analyzed by means of scanning electron micrograph (SEM) equipped with an energy dispersive spectroscopy X‐ray (EDX) analysis system.

It was found that the thickness of the IMC layer at the interface of a Cu/SACBE/Cu joint was remarkably thinner than that of a Cu/SAC/Cu joint. The addition of Bi and Er could significantly improve the tensile properties of the solder joint and enhance its resistance to high temperature aging. A mixture of ductile and brittle fracture mode was observed after tensile testing in the Cu/SACBE/Cu joints.

The paper implies that the addition of Bi and Er could complement effectively the effects of Ag, thereby reducing the cost of solder. The low‐silver SACBE solder is a potential alloy for electronic packaging production.

Sn‐Zn based lead free solders with a melting temperature around 199°C are an attractive alternative to the conventional Sn‐Pb solder and the addition of bismuth improves its wetability. Whilst lead‐free soldering with Sn‐8Zn‐3Bi has already been used in the electronics assembly industry, it is necessary to study its low cycle fatigue properties since such data have not been reported up to now.

In this study, displacement‐controlled low cycle fatigue testing of Sn‐8Zn‐3Bi and Sn‐37Pb solder joints was done on lap shear samples. The test amplitude was varied whilst the frequency was kept constant at 0.2 Hz and failure was defined as a 50 per cent load reduction. Finite element (FE) modelling was used for analysis and the results were compared to the experimental data.

The microstructure of the Sn‐8Zn‐3Bi solder showed a mixed phase of small cellular‐shaped and coarser needle‐shaped areas. Au‐Zn intermetallic compounds were observed near the interface from the SEM‐EDS observation. The average lifetime for the Sn‐8Zn‐3Bi solder joints was 17 per cent longer compared to the Sn‐37Pb solder joints. The cross section observation indicated that the fatigue cracks propagated along the interface between the solder bulk and the Au/Ni layer. The locations of maximum equivalent stress from the FE simulation were found to be at the two opposite corners of the solder joints, coinciding with the experimental observations of crack initiation.

This is believed to be the first time, the low cycle fatigue properties of Sn‐8Zn‐3Bi solder have been reported.

To determine the Coffin‐Manson (CM) equation constants for fatigue life estimation of Sn‐8Zn‐3Bi solder joints, since Sn‐8Zn‐3Bi solder has a melting temperature of around 199°C which is close to that of the conventional Sn‐Pb solder which has previously been used in the electronics assembly industry.

Three dimensional finite element (FE) simulation analysis was used for comparison with the experimentally measured data and to determine the CM constants. Low cycle fatigue tests and FE simulations were carried out for these lead‐free solder joints, and eutectic Sn‐37Pb solder was used as a reference.

The CM equation for Sn‐8Zn‐3Bi solder joints was fitted to the lifetimes measured and the shear strains simulated. The constants were determined to be 0.0294 for C, the proportional constant, and for the fatigue exponent, β, −2.833.

The CM equation can now be used to predict the reliability of Sn‐8Zn‐3Bi solder joints in electronics assembly and the knowledge base for the properties of the Sn‐Zn solder system has been increased.