Keju Ji

The Tribological Behaviors of Self-Lubricating Composites as Filler in Copper Foam

A copper foam–based (CFB) self-lubricating composite was developed as a friction pair material. The composite consists of copper foam with three-dimensionally interpenetrated pores and solid lubricant fillers (polytetrafluoroethylene [PTFE] and MoS2). The thermal and electrical conductivity, bending strength, and tribological properties of the new composite were investigated. The friction and wear properties were investigated on a M-2000 model ring-on-block test rig. An electric field was imposed between the sample and ring to monitor the tribochemical reaction and formation of transfer film by means of contact resistance. Measurement of friction temperature was carried out by means of three thermocouples embedded in the material. The friction coefficients of the CFB composite decrease slightly, and the wear rate substantially decreased overall compared with that of the homologous polymers. The optical and scanning electron micrographs (SEM) of the frictional surfaces show the worn surface of the CFB composite. The main wear mechanism was three-body abrasion, caused and promoted by plastic deformation, abrasive wear, and fatigue spalling. X-ray photoelectron spectroscopy (XPS) analysis showed that the reactions of MoS2 with Cu accompanied by their respective oxidation reactions are involved in the identifiable copper area.

Centrifugation-Assisted Fog-Collecting Abilities of Metal-Foam Structures with Different Surface Wettabilities

The collection of water from fog is a simple and sustainable means of obtaining freshwater for human and animal consumption. Herein, we address the use of metal foam in fog collection and present a novel fog-collecting device fabricated from copper foam. This device, which can also be used in other liquid-gas separation applications, is a 3D extension of biologically inspired 1D and 2D materials. The network structure of the 3D material effectively increased the contact area and interaction time of the skeleton structure and fog compared to those of traditional 2D fog-collecting materials. The main aspects investigated in this study were the influences of the inertial centrifugal force generated by rotating the metal-foam samples and the use of samples with different surface wettabilities on the fog-collecting performance. Superhydrophilic and superhydrophobic samples were found to have higher collection efficiencies at low and high rotational speeds, respectively, and a maximum efficiency of 86% was achieved for superhydrophobic copper foam (20 pores per inch) rotated at 1500 rpm.

Tribological behaviors of foamed copper/epoxy resin composites augmented by molybdenum disulfide and multi-walled carbon nanotubes

A novel foamed copper/epoxy (FCE) composite possessing improved wear resistance was developed as a rubbing pair material. The composites consist of an open-cell foamed copper skeleton and an epoxy resin and auxiliary additives, such as molybdenum disulfide (MoS2) and multi-walled carbon nanotubes (MWCNTs). A universal UMT-2 friction and wear tester was utilized to study the tribological properties of the FCE composites under dry lubrication conditions. We found that the amount of MoS2, the porosity of the copper foam, and the presence of the MWCNTs all have an effect on the friction and wear properties of the composite materials. The friction coefficient of the composite material gradually decreases as the amount of MoS2 increases; however, the wear rate initially decreases and then increases. When the MoS2 content is 30%, the wear rate reaches a minimum. The wear rate decreases as the porosity of copper foam decreases, but porosity has little effect on the friction coefficient. As the rotation speed of the grinding steel plate and the applied load on samples increase, the wear becomes more significant. The presence of MWCNTs also increases the strength and wear resistance of the epoxy resin matrix. Depth-of-field microscopy and scanning electron microscopy were employed to observe the worn-surface morphologies and wear mechanism. The worn surface of the FCE composite matrix is divided into three parts: the hollow metallic copper skeleton region, the polymer zone, and the transition zone copper skeleton that contains some polymer material. It is important to note that the wear mechanism of the various compositions is adhesive wear and slight abrasive wear, and the fatigue crack that runs perpendicular to the direction of movement begins to form at higher speeds, which results in a higher wear rate.

Super-floatable multidimensional porous metal foam integrated with a bionic superhydrophobic surface

Creating superhydrophobic surfaces is an important direction for porous materials used in water. We report a novel kind of super-floatable material fabricated from superhydrophobic metal foam as a three-dimensional extension of biologically inspired 1-D and 2-D materials. A simple and widely adaptable method is used to construct a superhydrophobic surface on the metallic skeleton of the copper foam with the pore sizes in the range of 0.5–4.2 mm. The force measurement procedure of the superhydrophobic copper foam in the process of sinking and floating is investigated. These 3D superhydrophobic surfaces are found to enable the metal foam to not only float freely on water, but also to exhibit a high loading capacity and sink resistance. The pore size of the sample is an important parameter reflecting the loading capacity. The smaller the pore size is, the higher the loading capacity. The maximal loading capacity of the sample is about 0.97 g cm−3, nearly equivalent to that generated by an air bubble of the same volume in water. Such porous metal foam mimicking the legs of water striders is expected to extend metal-based floatable materials from 1D metal threads and 2D metal meshes or sheets to 3D metal structures.

Different Foamed Metal–Reinforced Composites: Tribological Behavior and Temperature Field Simulation

Four kinds of foamed metals (foamed Ni, FeNi, CuNi, and Cu) filled with polytetrafluoroethylene (PTFE) and graphite were developed as rubbing materials. These open-cell foamed metals had the same interconnected three-dimensional (3D) metallic skeletons. The friction and wear properties of the new composites were investigated on an M-2000 friction and wear tester. To study the influence of the metallic skeleton on the contact between the sample and the rotating ring, an electric field was imposed to monitor the formation of transfer film by means of contact resistance. A thermocouple was embedded into the sample to measure the temperature variation caused by friction. Optical and scanning electron microscopes were used to study the worn surface morphologies. The temperature field of the sample and the effect of the metallic skeleton on temperature were calculated using finite element analysis (FEA). It was found that the foamed metal–reinforced composites possessed better thermal conductivity and wear resistance than homologous polymers, which was attributed to the following two main reasons: first, the metallic skeletons are beneficial for restraining the plastic flow of polymeric matrix and second, the heat can be conducted along the 3D supporting skeletons effectively.

Foamed-metal reinforced material: tribological behaviours of foamed-copper filled with polytetrafluoroethylene and graphite

A novel foamed copper based (FCB) composite is developed as a rubbing pair material. The composites consist of the foamed copper and solid lubricants, such as polytetrafluoroethylene and graphite. Four kinds of FCB composites were fabricated by vacuum filtration, compression moulding, and sintering process in an orderly manner. The thermal and electrical conductivities and tribological properties of the new composites were investigated. Because the interconnected metal skeletons have been embedded in the polymers, the FCB composites possess excellent thermal and electrical conductivities, including nice self-lubricating property. The friction and wear properties were investigated on an M-2000 friction and wear tester. An electric field was imposed between the sample and ring to monitor the tribo-chemical reaction and formation of transfer film by means of ‘contact resistance’. The measurements of friction temperatures were carried out by means of three thermocouples embedded in the material. The friction tests show that the friction coefficients of the FCB composites decrease almost monotonically with the increase of graphite content under different conditions; and the wear rates decrease overall compared with that of the homologous polymers, more obvious especially under severe conditions. The optical microscope, SEM, and XPS were adopted to study the worn surface morphologies and the transfer films. The main wear mechanism of the new composite is a three-body abrasion, caused and promoted by the plastic deformation, abrasive wear, and fatigue spalling. The oxidation of copper is the dominant chemical processes which occurred during the sliding process.