Tribological behaviour of sintered iron based self-lubricating composites (original) (raw)
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ABM Proceedings
In order to better understand the tribological behavior of self-lubricating materials, Fe-Si-C matrix composites containing solid lubricants added during the mixing step were studied. The samples were produced by conventional powder metallurgy route, presenting total contents of 5%, 7.5% and 10% in volume of h-BN and graphite mixtures as solid lubricants. The composites were evaluated in terms of tribological properties, under reciprocating sliding conditions, and mechanical properties by using tensile tests. Additionally, the wear scars were characterized by Raman spectroscopy and scanning electronic microscopy. Higher total contents of solid lubricants greatly increased scuffing resistance however decreased mechanical properties. Furthermore, increasing h-BN contents reduces both properties. These results confirmed the applicability of such sintered composites as self-lubricating parts, reaching values up to 7000 N.m for scuffing resistance combined with ultimate tensile strength of 220 MPa.
A series of Fe-Cr matrix high temperature self-lubricating composites were prepared by powder metallurgy technique (PM). The tribological properties of composites sliding against ceramic Si 3 N 4 ball were studied by using a ball-on-disc high-temperature tribometer at 10 N and 0.19 m/s for 20 min from room temperature to 800°C. Mo element showed an obvious solid solution strengthening effect on the matrix, and formed the high temperature solid lubricant BaMoO 4 . The obtained results showed that the tribological properties of specimens greatly depended on the additives. Generally speaking, the specimen containing 8.0 wt.% BaF 2 , 10.0 wt.% Ag and 8.5 wt.% Mo kept the lowest friction coefficient (0.4) and specific wear rate (1.8-3.7 Â 10 À4 mm 3 N À1 m À1 ) from room temperature to 800°C. The high-temperature tribological properties of Fe-Cr based alloy were improved due to the addition of additives. The excellent tribological behavior of specimen was attributed to the synergetic action of solid lubricants and high hardness. The wear mechanism of specimen FM is ploughing and slightly delamination at room temperature and 400°C. At 800°C, the specimen FM shows the micro-ploughing characteristics.
Lubricants
Sintered iron-based self-lubricant composites in which graphite reservoirs are generated by the dissociation of silicon carbide (SiC) particles feature low friction coefficients and scuffing resistance combined with high mechanical stress. This work evaluated the influence of the sintering temperature and the SiC polytype on the graphite reservoirs morphology, structure, and friction behaviour. The reservoirs were studied by field emission gun-scanning electron microscopy (FEG-SEM), micro-Raman spectroscopy, and transmission electron microscopy (TEM). The friction behaviour was evaluated by cylinder on plane tests (friction coefficient and scuffing resistance). The results showed that the SiC polytype and the sintering temperature modified the graphite structures. The SiC dissociation promoted the formation of different nano graphites, presenting different turbostratic 2D and 3D arrays. The results showed that the presence of the turbostratic graphite was beneficial to the friction ...
High Temperature Tribological Characteristics of Fe–Mo-based Self-Lubricating Composites
Tribology Letters, 2009
Fe-Mo-based self-lubricating composites were prepared by a powder metallurgical hot-pressing method. The tribological properties of Fe-Mo-based composites with varied CaF 2 contents at high temperature were evaluated, and the effect of glaze films on the friction and wear characteristics of composites were analyzed. The results show that the introduction of CaF 2 into Fe-Mo alloys improved the mechanical properties, and the best tribological properties of Fe-Mo-CaF 2 composites were achieved at the CaF 2 content of 8 wt% at both room temperature and 600°C. The worn surface of Fe-Mo-CaF 2 composite at 600°C is characterized to plastic deformation and slight scuffing, and the improved tribological properties are attributed to the formation of lubricious glaze film that composed of high-temperature lubricants CaMoO 4 and CaF 2 on the worn surface of the composites.
Lubricants
Innovative nanostructured materials offer the possibility of enhancing the tribological performance of traditional materials like graphite and molybdenum disulfide (MoS2). In this study, the scratch resistance of two different copper powders, dendritic and spherical, and their composites with traditional MoS2, nanometric MoS2, and graphene nanoplatelets was investigated. Metal powder metallurgy was employed to produce composite materials with 5 wt% and 10 wt% of each solid lubricant. A ball milling step was employed to grind and mix the matrix copper powder with the lubricants. The use of a cold press combined with the sintering in inert atmosphere at 550 °C limited the oxidation of the copper and the degradation of the solid lubricants. The so-produced materials were characterized through a variety of techniques such as micro-indentation hardness, electrical resistivity, contact angle wettability, X-ray diffraction, Raman scattering, and scanning electron microscopy. Moreover, micr...
Tribological and mechanical properties of PM Fe-Cu-Sn alloy containing graphite as a solid lubricant
World Review of Science, Technology and Sustainable Development, 2018
The mechanical and tribological properties of Fe-Cu-Sn alloy containing graphite as a solid lubricant were investigated. An attempt is made to develop graphite added Fe-Cu-Sn alloy using simple single stage compaction and sintering of elemental powders. The influence of varying compositions of graphite on the mechanical and tribological properties of the sintered alloys was studied. The tribological behaviours of sintered alloys sliding against EN8 steel ball under dry sliding conditions were studied using a ball-on-disk tribometer. The composition containing 3 wt% graphite shows better mechanical properties due to the formation of Cu-Sn, Fe-Cu and Fe-Sn compounds in large amounts at the high sintering temperature. The friction coefficient of Fe-Cu-Sn alloy decreases by 60% with increase in sliding distance with variation from 0 wt% to 3 wt% of graphite content. The higher amount of graphite content is found to be beneficial in improving wear resistance. The wear mechanism of Fe-Cu-Sn alloy containing 0 wt% of graphite is adhesive wear and abrasive wear. However, the wear mechanism of Fe-Cu-Sn alloy containing 3 wt% of graphite is mildly abrasive wear.
Aiming the production of self-lubricating parts by conventional route of powder metallurgy, Fe-Si-C matrix composites with embedded hexagonal boron nitride and graphite as solid lubricants added during the mixing step, were studied. Tribological and mechanical properties were evaluated in these composites presenting varied contents in volume of solid lubricant and for each percentage, different proportions of hexagonal boron nitride and graphite. The powder mixtures were evaluated in terms of flow rate and apparent density and the composites in terms of tensile strength, hardness and scuffing resistance. A decrease in apparent density and flowability of mixtures was observed when increasing the total volume of solid lubricant, however apparent density increased when higher proportions of hexagonal boron nitride were used. Increased total contents of solid lubricant greatly raised scuffing resistance despite decreased mechanical properties, especially when higher proportions of h-BN ...
Superior tribological properties of powder materials with solid lubricant nanoparticles
Wear, 2003
Friction and wear of powder materials impregnated with commercially available layered (platelets) WS 2 (2H) and inorganic fullerene-like WS 2 nanoparticles (IF) were studied. Bronze-graphite, iron-graphite and iron-nickel-graphite samples were used in this experiment. The linear wear of powder materials (in situ) was measured. It was shown that the IF nanoparticles impregnated into the pores improve the tribological properties of powder materials in comparison to a reference sample or the sample impregnated with 2H solid lubricant particles. The mechanisms of friction and wear of the IF nanoparticles have been considered. The tribological role of the wear particles and nanoparticles of solid lubricants has been analyzed in the framework of a third body lubrication model. The state of the IF nanoparticles before and after the wear test was studied. It was found that the shape of the IF nanoparticles is preserved during the friction tests under high loads. Thin wear debris surrounded by spherical IF nanoparticles appear to be formed and provide easily sheared lubrication film (low friction coefficient) during friction experiments of powder materials containing IF nanoparticles.
Tribological Behavior of Ni-Based Self-Lubricating Composites at Elevated Temperatures
Processing Techniques and Tribological Behavior of Composite Materials
This chapter illustrates the effect of the addition of solid lubricants on the high temperature friction and wear behavior of Ni-based composites. Ni-based composites containing solid lubricant particles both in nano and micrometer range have been fabricated through powder metallurgy route. In order to explore the possible synergetic action of a combination of low and high temperature solid lubricant, nano or micro powders of two or more solid lubricants were added in the composites. This chapter introduces the fabrication of the Ni-based self-lubricating composites containing graphite and/or MoS 2 , Ag and/ or rare earth, Ag and/or hBN as solid lubricants and their friction and wear behavior at room and elevated temperatures. The chapter also includes information on some lubricating composite coatings such as electro-deposited nickel-base coating containing graphite, MoS 2 , or BN and graphene and their tribological characteristics.
Lubricants
In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron and that the combination of MoS2 + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant’s particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 × 10−6 mm3·N−1·m−1) were achieved.