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The production of self-lubricating composites containing second phase particles is one of the most promising choices for controlling friction and wear in energy efficient modern systems. To gain a better understanding of the wear behaviour of such materials, Fe-Si-C matrix composites containing solid lubricants added during the mixing step were studied in this work. The samples were produced using powder metallurgy route, with total contents of 5, 7.5 and 10% in terms of volume of hexagonal boron nitride (hBN) and graphite mixtures as the solid lubricants. The composite's tribological properties were evaluated under reciprocating sliding conditions and their mechanical properties were tested using tensile tests. Additionally, after interruptions at different stages of the reciprocating tests, the wear scars were characterised by Raman spectroscopy and scanning electronic microscopy, to evaluate the evolution of the wear with test time. Higher total solid lubricant contents greatly increased the scuffing resistance of the composites, but decreased the mechanical properties. Furthermore, increasing the hBN content reduced both properties. Among the composites studied, the samples containing 1% vol hBN and 9% vol graphite showed the best combination of mechanical and tribological properties.

The shape and dimensions of the component play an essential role in plasma nitriding processes, a surface treatment crucial for the powder metallurgy industry since salt bath and gas nitriding poorly interact with porous structures. When the geometry of the components contains cavities, holes, or even parallel flat surfaces, the hollow cathode effect (HCE) can be activated, and, as a consequence, microstructural transformations that develop columnar nitride compound layers and the formation of a N-rich eutectoid, the braunite, may occur. The tribological properties of nitride compound layers with microstructural characteristics induced by the hollow cathode effect were evaluated in this work. Hollow cylinders of sintered iron were plasma nitrided and the tribological behaviour was assessed via reciprocating dry sliding tests. Unlike the friction coefficient, which is high (~0.4) regardless of the surface treatment, the wear rate is strongly increased by the presence of columnar morphology (2.4x) and braunite layer (2.1x), which are at the origin of brittle mechanisms such as crack propagation and interaction, resulting in the detachment of the compound layer.

Copper is a well know material for use as heat sink or heat exchanger. However, copper has a considerable low tensile strength and temperature limit. A material that has a good thermal conductivity, low cost, but also resistance is the desired. Effects of copper on the sintering and thermal properties of iron-copper composites produced by powder metallurgy and Fe on copper-iron composites have been investigated. Copper and iron were varied from 20 to 80 vol.% in the samples, alternating the continuous phase. Sintering studies were performed by in-situ dilatometry aiming to define the proper conditions for sintering, without swelling normally associated with copper. Results indicate that the type of sintering, final microstructure, specially the phases relation and distribution and not only the amount of copper, have a great effect into the thermal properties. By controlling the sintering parameters, it is possible to obtain dimensionally stable samples with higher thermal conductivity and lower copper amount.

The purpose of this work was to develop nickel self-lubricating composites using solid lubricant as second phase and obtained by powder metallurgy. The work involved the study of chemical stability and chemical interaction between the nickel alloy matrix and solid lubricating additives (molybdenum disulfide, graphite and hexagonal boron nitride). The results showed a thermodynamic stability during sintering for the composites containing the phases of graphite and hexagonal boron nitride. The presence of molybdenum disulfide phase permits a reaction with the matrix, the formation of a liquid phase of nickel sulfide and the solubilization of molybdenum in the matrix.

The production of self lubrication composites containing second phase particles incorporated into the volume of the material appears to be a promising solution. A new processing route to obtaining a homogeneous dispersion of discrete solid lubricant particles in the volume of sintered steels produced by metal injection molding (MIM) was recently presented. This new route was achieved by in situ formation of graphite nodules due to the dissociation of precursor (SiC particles) mixed with the metallic matrix powders during the feedstock preparation. Nodules of graphite (size ≤20 μm) presenting a nanostructured stacking of graphite foils a few nanometers thick were obtained. The thermal debinding, as well as the sintering, was performed in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. In this work, we present and discuss the effect of precursor content and sintering temperature on the scuffing resistance of plasma assisted debinded and sintered self lubricating steel produced by metal injection mould technique. Three different temperatures (1100, 1150 and 1200 °C) and six different SiC contents (0–5%) were analyzed. Increasing the precursor content and, as a consequence, the number of graphite nodules, produced a clear increase in scuffing resistance for all analyzed sintering temperatures. Friction coefficient was little affected by the sintering temperature. However, the scuffing resistance was greatly increased (5×) for the lower sintering temperature (1100 °C).

Strong materials that combine wear resistance with low coefficients of friction can be tailored to suit particular engineering applications. That's just one example from materials scientists in Brazil that illustrates the possibilities for increasing efficiency, while scoring environmental points by cutting waste…

Friction and wear control can be achieved primarily by considering the nature of the counter faces, together with the environmental conditions. In most cases, a transfer film is found on the sliding surfaces. The environment plays a crucial role on the kinetics of formation and on the composition of the transfer film, and thus strongly influences friction level and wears rates. In this paper, the effect of the actual environment (refrigerant) present in hermetic compressors on the tribological behaviour of a Si-rich multifunctional DLC coating deposited on 1020 steel and tested against 52100 steel pins was analyzed. Unlubricated reciprocating pin-on-disk tests were performed using a high pressure tribometer (HPT) under different atmospheres (air, CO 2 and R600a). The tribological behaviour (friction coefficient and wear rate results) was analyzed using laser interferometry, scanning electron microscopy and micro-Raman spectroscopy. Samples tested in R600a environment presented the lowest friction coefficient and the lowest wear rate for both body and counter-body.

Steam oxidation is an important industrial procedure for changing tribological properties, sealing porosity and improving aesthetics in sintered iron components. Manganese phosphate coatings are believed to have intrinsic lubricant properties and very low friction coefficients. In this work, after steam oxidation, sintered iron components were coated with manganese phosphate and their tribological behaviour was investigated. Components with two nominal film thicknesses were compared, either coated or uncoated with manganese phosphate. Their abrasion resistance was evaluated using micro abrasion wear tests. Reciprocating wear tests were used to study their sliding wear resistance. It was observed that phosphating of the oxidized samples resulted in an increase of the wear rate in both tests. Phosphating promoted a reduction of the oxide film thickness, probably due to the chemical conversion reaction with the oxide substrate. The reduction of wear resistance due to phosphating was associated with a reduction of oxide film thickness.

The tribological characterization, in particular the surface durability of multifunctional layers applied to soft, non-magnetic materials, due to their important differences in mechanical and tribological properties, constitutes, by itself, an important challenge to the tribologist. These multifunctional layers consist of a solid lubricant coating on top of a hard, wear resistant and high load-supporting layer. The use of low severity conditions, which are necessary to discriminate between solid lubricants, induce unnecessary and unduly long test times. The use of high severity conditions, which are more adequate to analyse the hard, high load supporting layers, produce shorter tests but are not able to discriminate among the solid lubricant deposits. In this paper, a new methodology allowing short test time with good discrimination between multifunctional layers is proposed. The test protocol is based on a method of incremental loading. By increasing the normal load in increments at a constant time interval the surface durability of both the hard layer and the solid lubricant coating was determined. The suitability, reliability and reproducibility of the proposed methodology were determined by testing commercially available solid lubricants (DLC, Teflon ® , MoS 2 dispersed in an inorganic binder and MoS 2 dispersed in an organic binder) coated on commercial aluminium (as received and as anodised).

Steam oxidized sintered iron-based materials have been, and continue to be used for load bearing parts in sliding contacts. Although the permanence of an oxide layer on the external surface is reported to be the main factor affecting tribological behaviour, in industrial practice as well as in laboratory tests abrasive wear is reported to play an important role in the final stage of the process. The removal of the superficial oxide layer, its fragmentation and transfer to the counter-body associated with metallic debris generation, induces the formation of hard debris particles acting as abrasives on the tribological system. In this paper, abrasive wear of steam-treated sintered iron is analysed by means of micro-abrasion tests. Sixteen specimens were produced from atomised iron powders (Ancor Steel 1000B Hoganas) of different sizes ( 125 μm). They were compacted at four different pressures (300, 400, 500 and 600 MPa), sintered for 30 min at 1120 °C and then subjected to continuous steam treatments at 540 °C for 2 h. The micro-abrasion tests were conducted under constant load and speed conditions while special emphasis was given to the nature of the abrasive; two exogenous (Al 2 O 3 and SiO 2 ) and one endogenous abrasive (Fe 2 O 3 ) were used. The results show that the abrasion resistance is strongly influenced by the processing parameters, the lowest wear coefficients were obtained by using the highest compaction pressures and the smallest powder grade. The pore size is the main micro-structural parameter affecting the abrasive resistance. For all abrasives, interrupted tests showed that the small pores are completely filled by abrasive particles in the initial stage of the tests while the biggest ones remains open until the completion of the tests. Wear coefficients were strongly influenced (up to 10 times) by the abrasive nature. Scanning electron microscopy analysis showed that the abrasive wear mechanisms were determined by the abrasive particle features.

Steam oxidation has proven to be an effective process to improve the properties of sintered iron components. The oxide formed on the surface and in the interconnected porosity strongly influences both the tribological and mechanical properties of these materials, for example through the extent of pore closure and the nature and morphology of the oxide produced. In this paper, the influences of compaction pressure and powder size on the microstructure, oxide content, hardness, and surface topography of steam treated sintered iron are analysed. Specimens prepared from atomised iron powders of different sizes ( 125 µm) were compacted at four different pressures (300, 400, 500, and 600 MPa), sintered for 30 min at 1120°C and then subjected to a continuous steam treatment at 540°C for 2 h. A clear influence of the processing parameters on porosity was highlighted. Low porosity was always associated with high compaction pressure and greater powder size. Pore size was affected in ...