Papers by Keyword: Self-Lubricating

Abstract: Self-lubricating spherical plain bearings are widely used in industry due to their high load capacity, excellent self-lubrication performance and superior impact resistance. The composite made of PTFE/Nomex fabrics and phenolic resin is selected as self-lubricating liners because of the great tribological properties. In this study, the effect of stress during press-fitting process on the tribological behavior of the composite liners in bearings was investigated. Five levels of stresses within a range of 0MPa~680MPa were firstly applied by upsetting process, and then ball-on-disk friction tests were conducted to evaluate the tribological properties. The variation of measured friction coefficient over testing time under different stresses was measured, and the microscopic surface morphology before and after friction tests was observed. Results show that the stress generated during the press-fitting process increases the friction coefficient, while decreases the fluctuation of friction coefficient. In addition, the fluctuation amplitude of the friction coefficients introduced by stress reaches 5.6%.

Abstract: In this paper, the dry cutting performance of Al₂O₃/TiC-based ceramic composites with nanoCaF₂ was studied. Compared with the Al₂O₃/TiC ceramic tool, the Al₂O₃/TiC/CaF₂ ceramic tool has lower cutting force, cutting temperature and surface roughness when milling 40Cr hardened steel. Three cutting parameters of cutting speed, feed per tooth, and cutting depth were used to conduct orthogonal experiments to study its changing trend. Through testing of cutting force, cutting temperature and surface roughness, and by comparison with ceramic tools without nanosolid lubricant added, the order of influence of three cutting parameters on cutting force, cutting temperature and surface roughness was obtained. The experimental results showed that the cutting force, cutting temperature and surface roughness of Al₂O₃/TiC/CaF₂ ceramic tools containing nanoCaF₂ werebetter than those of Al₂O₃/TiC ceramic tools. The cutting force, the cutting temperature, and the surface roughness were respectively reduced by 16.5%, 25.8% and 43% compared to when no solid lubricant was added. In addition, after adding solid lubricant, the effect of cutting depth on cutting force was significantly reduced. The average friction coefficient of the tool rake surface was 31.1% lower than that of ceramic tools without solid lubricant. In order to explain this phenomenon, through scanning electron microscopy (SEM) scanning and energy spectroscopy (EDS) elemental analysis, the wear reduction mechanism of solid lubricants was analyzed, that is, during the cutting process, nanosolid lubricants precipitated and formed lubricating film on the rake surface of the tool to reduce the friction coefficient. This was also the main reason for reducing the cutting temperature.

Abstract: Self-lubrication composites containing second phase particles incorporated into the volume of the material appears to be a promising solution for controlling friction and wear in modern systems. The objective of this work was the development of steels with low friction coefficient using granulated powders through a precursor (SiC), which generate carbon nodules in a ferrous matrix. The studied alloy composition was Fe+0,6C+3SiC using 2 wt.% of EVA as binder. In this study, the influence of the average size of the iron particles and silicon carbide (SiC) in the microstructure, mechanical and tribological properties was evaluated. The powders were first mixed in a "Y" type mixer, granulated drum, compressed and sintered in plasma in a single thermal cycle assuring binder extraction and sintering of components. The achieved results were close to those of alloys of the same composition produced via powder injection molding (PIM) but with processing time and cost close to those of conventional powder metallurgy (PM). Materials with yield strength of 250 MPa, durability of 2800 Nm and 0.11 friction coefficient were obtained.

Abstract: In this paper an adaptive Ni-Mo-Al-Ag-BN composite coating was deposited by plasmaspraying. Its tribological property from 20°C-600°C were evaluated by using high temperature tribometer. Scanning electron microscopy and Raman spectroscopy were used to characterize the coating and corresponding wear tracks to determine the lubrication mechanisms. The result shows that the friction coefficient of the Ni-Mo-Al–Ag-BN composite coating from 200°C to 400°C is about 0.4 and declines very slightly at 600°C . The wear rates of the coating is 2.0×10^-4mm³/N*m at 600°C and the downward trend is obvious compared with 400°C. Silver provide lubrication below 400 °C. Ag₂MoO₄ were formed with the temperature raised, and acted as high-temperature lubricants above 400 °C. Ni-Mo-Al–Ag-BN composite coating established a new lubrication mechanism model at 600°C . It can be concluded that the plasma sprayed Ni-Mo-Al - Ag - BN composite coating can keep good tribological property at wide range of temperature.

Abstract: Ti-Al alloy matrix self-lubricating composites were fabricated by the method of high temperature hot pressing sintering. The friction and wear performance of self-lubricating Ti-Al matrix composites were studied at high temperature. The study found that the friction coefficient decreased with the increase of solid lubricant, CaF2 and BaF2 had played good lubrication. when the lubricant BaF2-CaF2 mass fraction was 10%, the wear rate of composites to the lowest, it was 0.29×10⁻⁷ cm³N^-1m^-1 in 650°C high temperature.

Abstract: Aiming at the low mechanical property of existing self-lubricating ceramic cutting tool material, a new Al₂O₃ based nanomicro composite gradient self-lubricating ceramic tool material was developed by applying the design concept of nanomicro composite. The self-lubricating ceramics was composed of ceramic matrix and self-lubricating component, and was prepared by hot pressing technology at a hot-pressing temperature of 1650°C, pressure of 30MPa, and duration of 15min. The model of gradient ceramic tool material is symmetrical composition distribution, and the compositional distribution n and layer number are 1.8 and 7, respectively. The result shows that the interfaces between layers are bonded well and no cracks or defects can be observed. Compare with the homogeneous material, the flexural strength, hardness and fracture toughness of Al₂O₃ based graded material increase by 74%, 5.2% and 3.9%, respectively.

Abstract: A series of Ti-48Al-2Cr-2Nb/62%BaF2-38%CaF2 (CB) self-lubricating composites with addition of different weight percentage of solid lubricant were prepared by vacuum hot pressing sintering. Sliding wear tests against 45#steel were performed on the specimen in dry conditions, worn morphology was observed by the scanning electron microscope (SEM). The test results show that when addition of solid lubricant weight percentage is 10%, the worn surface of the composites is most smooth.The main wear mechanisms of Ti-48Al-2Cr-2Nb/62%BaF2-38%CaF2 composite are abrasive wear and adherent wear.

Abstract: TiB₂/WC/h-BN micro-nano composite gradient self-lubricating ceramic tool material was prepared by vacuum hot-pressing technique. The mechanical properties were tested and compared. The best flexural strength, fracture toughness and Vickers hardness of the tool material were 678MPa, 4.75MPa·m^1/2 and 15.1GPa, respectively. The microstructure was analyzed by thermal field emission scanning electron microscope (SEM). TiB₂ nanoparticles were obviously observed in the ceramic matrix. It suggested that the developed TiB₂/WC/h-BN micro-nano composite gradient self-lubricating ceramic tool materials will have potential application in dry machining.

Abstract: A new nanomicro composite self-lubricating ceramic tool material was prepared with vacuum hot pressing technique. The effect of nanoAl₂O₃ powders on the microstructure and mechanical properties of nanomicro composite self-lubricating ceramic tool material was investigated. With the increase of nanoAl₂O₃ content, the hardness and fracture toughness first up then down. When the nanoAl₂O₃ content is 4 vol.%, the flexural strength, hardness and fracture toughness reaches 562 MPa, 8.46 MPa·m^1/2 and 18.95 GPa, respectively. The microstructure and mechanical property of nanomicro composite self-lubricating ceramic tool material can be improved by the grain refinement strengthening of nanoAl₂O₃.

Abstract: t is of great importance to find ways to lubricate ZrO₂ceramic. In this paper, a kind of ZrO₂ matrix high temperature self-lubricating compositewith addition of CaF₂ and graphite as lubricants was prepared by hot-pressing. It was found that the tribological properties of ZrO₂(Y₂O₃)-CaF₂-graphiteshow a good tribological behavior both at low temperature and high temperatures. The low friction coefficients of ZrO₂ (Y₂O₃)-Mo-CaF₂-graphite at high temperatures were due to the perfect lubricity of CaMoO₄ which was formed on the worn surface at high temperatures.