Papers by Keyword: Solid Lubricant

Abstract: The manufacturing industry has a significant impact on the economy of a country. Therefore, carrying out necessary developments and modifications in manufacturing machine components is essential. Some materials, called superalloys, are challenging to machine, and they have a wide application in the turbine components of aerospace, submarines, oil, nuclear, steam, and other power generation industries. Due to the exceptional properties of these superalloys their machining becomes very difficult and time-consuming; They damage the cutting tool, and excessive use of lubricants eventually affect the material handling and cost. These problems lower down the sustainability and therefore an attempt has been made in the current research work to eliminate the use of cutting fluid by impinging solid lubricant on AlTiN coated tungsten carbide cutting tool by using pulsed direct current magnetron sputtering and cathodic arc physical vapour deposition techniques. The micro-texturing is first done on rake face of the milling insert such that graphite, which acts as a solid lubricant, can be then deposited in those micro-textures. The end milling of Nimonic 90, a superalloy, is done using the solid lubricant filled microtextured insert under compressed air environment, and the cutting forces, cutting temperature, tool wear, and surface roughness are analysed. It is found that there is a substantial decrease in the cutting forces and tool wear when compared with non-textured tool due to less friction and temperature at the machining zone. Sustainability of such solid lubricant based textured cutting tool has shown improvement when compared with non-textured cutting tool. The machinability of Nimonic 90 is increased by implementing the solid lubricant-based cutting tool, and therefore, it can be effectively utilised for the machining of superalloys soon.

Abstract: AA2219 is a superior performance Al-base alloy which promises toughness, strength and creep resistance which allows the deposition of titanium nitride (TiN) coating at 200 °C. The present research addresses the issue of poor wear properties of the alloy, using state of the art technologies, to deposit hard and adherent thin TiN layer followed by laser surface texturing. The thickness of sub-micron size coating is determined by appropriate modification of the existing mathematical model and composite microhardness values. Laser energy density of 20.8 J/cm² and 4 repeated pulses is optimized to produce regular size and shape of micro-holes on TiN-coated samples. Epoxy-based MoS₂ lubricant is deposited on laser textured samples to produce ultra-low friction surfaces. The micro-holes act as a micro-reservoir of MoS₂ solid lubricant. Field emission scanning electron microscope and optical profilometer were used to estimate the topology, shape, size, and depth of micro-holes. The cross-sectional view shows the successful impregnation of epoxy-based MoS₂ due to the chemisorption of functional groups with an Al oxide surface.

Abstract: High temperature applications of self-lubricated sliding surfaces have gained industrial importance during the recent years. One popular system is based on sintered Ni-Cr composites with addition of solid lubricants. In the present work these composites were prepared under controlled sintering conditions with different combinations of solid lubricants (MoS₂, Ag and CaF₂) at 1200 °C under flowing argon. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using SEM analysis while the hardness of the composites was measured by Vickers Micro Hardness Tester. The friction tests were conducted with ball on disc configuration following ASTM G-99-95a standard. The MoS₂ solid lubricant provides best lubrication at room temperature which is demonstrated by a low friction coefficient compared to pure Ni-Cr composites. The SEM pictures of worn out tracks show solid debris distribution, and filling of pores with solid lubricant phases. The time taken for stabilization of friction coefficient also varies with the type of solid lubricant. Dual and multiple additions of solid lubricants are also able to reduce the friction of coefficient compared to pure Ni-Cr composite.

Abstract: In order to increase the working efficiency of coated-carbide cutting tool under interrupted cutting conditions it is most efficient to use abrasion resistant refractory coating and solid lubricants.

Abstract: Aluminium matrix composites (AMCs) are indispensable materials used extensively in the aerospace and automobile industries and are highly endorsed due to their good mechanical properties. In this paper, various compositions of the AMCs were fabricated, tested and analyzed using pin on disc tribometer test to understand the tribological behaviour and wear mechanism properties. The volume percentages of the Aluminium composite reinforced with boron carbide and graphite present in the form of Al-B₄C-Graphite are Al-B₄C (5%)-Graphite (5%), Al-B₄C (10%)-Graphite (5%), Al-B₄C (5%)-Graphite (15%), Al-B₄C (10%)-Graphite (15%), Al-B₄C (15%)-Graphite (15%). Loads were varied in steps of 10N, from 10N to 50N while the sliding velocity was correspondingly set as 0.7, 1.4 and 2.1m/s. SEM image analysis was conducted to understand surface tribology after wear tests. The composite Al-B₄C (15%)-Graphite (15%) exhibited best wear resistance which can be credited to the bearing capacity of boron carbide particles and adherent graphite layer.

Abstract: Bronze based alloys have come to be used as bearing materials, and require low frictional properties. The present study describes the effects of surface finish machining history on the on tribological properties of sulfide-containing bronze sintered onto a steel disc. The sulfide phase consisted of copper, iron and sulfur, and acted as a solid lubricant. The relative density of the specimen was 90 % and the microstructure showed that the micro-sized sulfide dispersed into the bronze matrix and was accompanied by pores. Various processes, including cutting, burnishing, polishing were, applied to finish the surface. It was found that the area fraction of the sulfide phase depended on the cutting conditions. A further increase in the area fraction was achieved using roller burnishing after the cutting. Tribological properties were evaluated using chromium alloy steel (SUJ2) as the mating surface under dry conditions. The results showed that the friction coefficient depended on the surface finishing process. Therefore, the machining history had an effect on the frictional properties of the sulfide-containing bronze. Optimal cutting conditions for the sulfide containing bronze are also discussed.

Abstract: Polytetrafluoroethylene (PTFE) powder is used as a solid lubricant in commercial antifriction coatings. However, most of the matrix polymers are usually not compatible with virgin PTFE resulting in low dispersion and mechanical film stability and adhesion. In our research PTFE TF 2025 was irradiated by g-beam generating PTFE micropowder with persistant radicals and functional groups. These functional groups are able to perform a chemical grafting (cg) of polyamideimide (PAI) and modified PTFE-micropowder by reactive extrusion in melt. Based on grinded extrudates PAI-PTFE-cg dispersions were formulated followed by characterizing dispersion as well as film properties. It was found, that PAI-PTFE-cg dispersion comprises very small PTFE-particles at higher g-irradiation doses in homogeneous dispersions. In addition, all samples showed outstanding film flexibility. Basic tribological properties under mixed lubrication were studied by using a ring-on-disk tribometer. Finally, diluted dispersions were applied to a multi-surface sliding bearing (four segments) for testing in a hydrodynamic plain test bench.

Abstract: The wear resistance of the coatings on the basis of Cu–Mo–S with a copper friction pair was studied by tribological tests in argon and air environment. Microstructure of the coatings was investigated by transmission and scanning electron microscopy. Fiber-globular structure of the coatings was evaluated. Cu–Mo–S coatings can increase the wear resistance of a copper friction pair in ~ 71.7 and ~ 7.9 times in argon and air atmosphere, respectively. Decrease of friction coefficient of copper friction pair from 0.59 to 0.27 (with coating) has been observed during tribological tests in air environment.

Abstract: In this investigation, the influence of MoS2 on the mechanical properties of Al6061-Al2O3hybrid composites was studied. The composites of Al6061 alloy, AA 6061-6% Al2O3 and Al6061-6% Al2O3-2% MoS2 were manufactured using Stir casting method. These samples were examinedusing optical microscope for the dispersion of reinforcement (Al2O3 ) and solid lubricant (MoS2).The micro structure revealed that there were even distribution of the additives in the Al6061 matrix.The presence of these particles improved the mechanical properties of the composites. For these compositions flexural strength was found using 3 point bending test and impact strength was found using Charpy test. It was observed that the hardness, toughness and flexural strength values increases with the addition of Al2O3 and decreases with the addition of MoS2 to the second composition.

Abstract: The prime rationale for designers to choose titanium in their designs for aerospace applications is its relative low weight for a given strength level and its relative resistance to high temperature. Excellent biocompatibility makes titanium as ideal material for many biomedical applications. Even though the titanium products are either sintered or cast into required shape, there is a need for machining in order to produce intricate shapes. However machining of titanium alloys poses many serious problems owing to the reactivity of titanium at high cutting temperatures and rapid tool wear. An alternative method to overcome this is by reducing the cutting zone temperature. This can be achieved by the addition of solid lubricants to regular cutting liquids and using it as minimum quantity lubrication (MQL) strategy. In this study, hexagonal boron nitride (hBN) powder with different concentrations (5, 10, 15 wt %) was mixed with water and used as a lubricant. Turning experiments were performed with TiAlN coated Tungsten carbide insert for a constant speed and variable feed rates. For comparison purpose, machining was carried out under dry conditions. Results indicate that the cutting zone temperature reduced drastically on addition of solid lubricant hBN with water. MQL conditions showed that cutting zone temperature decreased by several folds when compared to dry machining. However there was no significant decrease in temperature between 10 and 15 wt% hBN additions which indicates that 10% hBN addition proves to be optimal. This type of machining thereby paves way for sustainable manufacturing.