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In the present work, we overview the multidisciplinary development of a regular, lubricated, hermetic compressor which works in an on-off cycle, circular motion, single-speed, many tribological contacts, into an innovative, linear motion, variable displacement, single tribological contact, oil-less hermetic compressor presenting high versatility in terms of refrigerator design, sustainability and improved efficiency. The original approach encompassed the development of new surface engineering procedures applying purpose-oriented phases to soft substrates. Particular emphasis is given to the in situ fluorination of the tribolayer formed in the piston-cylinder tribopair. Although chlorinated halocarbons (CFC) are efficient refrigerants from a thermodynamic point of view, they do have serious environmental implications that have forced the refrigeration industry to switch to more environmentally friendly hydrofluorocarbon (HFC) based refrigerants. The first and most successful alternative to the CFCs was tetrafluorocarbon, particularly tetrafluoroethane (CF3CH2F), aka R134a refrigerant. The current trend to downsizing mechanical systems, smaller clearances, and increased speeds leading to greater energy efficiencies associated with miscibility issues imposing the use of costly, fully synthetic lubricants with the R134a refrigerant gas led to the introduction of a new hermetic compressor design, the Wisemotion®, the first, and until now, unique, oil-free hermetic compressor on the world market. In this context different types of multi-layers, their thickness, substrate material, processing routes, etc., have been studied and optimized. Si-rich hydrogenated DLC (a:C-H) presented enhanced tribological properties when tested under fluorine-rich atmospheres, and semi-industrial scale tests have been carried out to understand this point further. A homemade tribological emulator was developed allowing close-to-real tribopair, atmosphere, and imposed mechanical conditions used in an oil-free commercial hermetic compressor. The tests were carried under different stroke frequencies (5, 20, and 40 Hz) and atmospheres (R134a, ambient air, and argon). Results showed a strong influence of both atmosphere and stroke frequencies. The friction coefficients were significantly lower (~3.8X) for the refrigerant gas atmosphere, attributed to the fluorine and highly disordered graphitic structures rich tribolayers. Under the high frequency (40 Hz), the energy input seems to be a deterrent to the formation of stable tribolayers, and the DLC coating shatters on the first few sliding meters.

Powder injection moulding and sintering were used to obtain iron-based self-lubricating composites in which SiC particles were used as precursors to generate graphite nodules dispersed in the composite matrix. Using thermodynamic simulations with DICTRA®, it was possible to predict the SiC dissociation in the ferrous matrix studied (Fe+0.6C). The evolution of the dissociation of SiC particles during sintering was investigated by X-ray diffraction (XRD) and dilatometric analysis, whereas the structure and morphology of the graphite nodules were studied by field emission gun-scanning electron microscopy (FEG-SEM), micro-Raman spectroscopy, and transmission electron microscopy (TEM). To compare the characteristics of the graphite nodules, micro-Raman and tribological analyses (friction coefficient and wear rate) were carried out for nodular cast iron and graphite powder. Reductions in the friction coefficient and wear rate of the tribological pair can be associated with the turbostratic characteristics of the graphite nodules.

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.

Purpose This paper aims to synthesize nanostructured flower-like molybdenum disulphide (MoS2) particles and evaluate their suitability to act as additives for lubricants. Design/methodology/approach A hydrothermal method without any surfactant successfully produced 250 nm mean diameter Nanostructured flower-like MoS2 particles. The resulting product was then solvothermally treated with absolute ethanol producing lipophilic powder particles which after being dispersed in two different lubricants were tribologicaly characterized by using a pin-on-disk tribometer geometry with reciprocal movement under immersion. Findings The influence on the stability and the coefficient of friction of the nano-oils is shown to be strongly dependent on their molecular structure. After 1 h of tribological testing, a ramified polyolester oil with 1 Wt.% of MoS2 nanoflowers did not show decrease in its average coefficient of friction, while an additive naphthenic oil with the same concentration of nanoparticles showed a decrease of 86 per cent. Originality/value In this paper, nanostructured flower-like MoS2 synthesized by the hydrothermal method was dispersed in lubricating oils to study its stability and tribological properties. To ensure good stability of the nano-oils, the particles were solvothermally treated with absolute ethanol to dehydrate and lipophilize them. A ramified polyolester-based nano-oil with 1 Wt.% of MoS2 nanoflowers showed no decrease in its steady state coefficient of friction, while a naphthenic-based nano-oil with the same concentration of nanoparticles presented a remarkable 86 per cent reduction.

The shape and geometry of the component play an essential role in surface plasma treatments. Certain plasma conditions can activate the hollow cathode effect (HCE) in parts with cylindrical geometry and, consequently, intensify the discharge by increasing the current density [1]. Due to this fact, a local surface over-heating can occur and cause some structural and microstructural transformation, developing columnar nitride compound layers and the appearance of braunite [2]. In this work, the tribological properties of nitride compound layers with microstructural characteristics induced by the hollow cathode effect (HCE) were evaluated. Hollow cylinders of sintered iron (7,5 mm in inner diameter and 9 mm in height) were plasma nitrided in three different conditions in order to obtain: a columnar compound layer (550 °C, 90%N2 + 9%H2 +1%CH4); a compound layer with presence of braunite (570 °C, 30%N2 + 70%H2); a compact and homogeneous compound layer with no microstructural defects (540 °C, 30%N2 + 70%H2). Pressure, output voltage and treatment time were kept constant in all treatments. The layer microstructures were analyzed by optical microscopy (OM) and the phase identification was conducted by X-ray diffraction (XRD). Reciprocating dry sliding tests were carried out to evaluate wear resistance and friction coefficient. White light interferometry was used to evaluate the surface topography and measure the wear volumes. The wear rate is affected by microstructural characteristics of the nitride layers induced by the HCE. Columnar nitride compound layer and the presence of braunite are undesired characteristics to achieve good wear resistance. Further-more, the friction coefficient was not influenced.

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.

This work presents the study and development of an iron-based soft magnetic composite containing double layer insulating coating constituted of zinc oxide nanoparticles and vitreous boron oxide. The combination of these two insulating compounds improves significantly the electrical and magnetic behavior of SMCs due to a synergistic effect between the layers during processing. Dynamic losses were reduced nearly 78% and electrical resistivity was increased in almost 10 times for the double layered SMC compared to an SMC containing only vitreous boron oxide coating. Moreover, the permeability was at least 10% higher in the double-layered SMC than in the one coated only by ZnO nanoparticles. On the other hand, tensile rupture strength of double-layered SMC matches the one observed for the SMC coated by ZnO, which is nearly 30% lower than the strength of sample coated by B2O3. A mechanism responsible for the observed synergy is proposed in this paper based on the electric and magnetic performance of produced samples, on the thermal behavior of the coating observed on TGA and on the SEM images taken from several stages of samples production.

The purpose of this work was to evaluate the influence of phosphorus quantity of the matrix of a nickel alloy on microstructure and hardness of nickel composite with hexagonal boron nitride – h-BN. The work was carried out using two nickel alloys with varying quantities of phosphorus (0.3 and 0.75 wt.%). The quantity of particles of solid lubricant added to the alloy was 10 vol.% of h-BN. The samples were compacted at 600 MPa and sintered at 1150 °C for 60 min in plasma. The results showed that the composite with 0.3 wt.% of phosphorus had hardness of 236 HV 0.025 (±34,25) and the composite with 0.75 wt.% of phosphorus had hardness of 326 HV 0.025 (±38,90), and formation of pellets of h-BN with a size between 50 and 100 μm and low porosity due to the formation of liquid phase of phosphide during sintering which carries the lubricant fine particles of approximately 10 μm dispersed in the microstructure during pore coalescence. As a result, the quantity of phosphorus present may influence the microstructura...

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).

This work aims to study the effect of refrigerant gases HFC134a and HC600a in components coated with DLC, Diamond-like Carbon, as well as is to establish a methodology for tribology evaluating of them. The tribological tests were conducted on a reciprocal motion. Balls of SAE 52100 steel and WC-Co were used as counter-body. The load was applied in a incremental way. The samples were prepared in SAE 1020 steel coated with DLC obtained from commercial suppliers. The characterization of samples was performed by optical interferometry and Scanning Electron Microscopy - SEM. It was verified a strong influence of the atmosphere through the in formation of a tribolayer at the interface between body and counter body. This influence showed disturbances in the coefficient of friction and contact resistance. Chemical analysis indicated that the tribolayer was formed by elements originated from the degradation of the refrigerants gases associated with of oxygen.

In the present investigation, the effect of plasma nitriding on the microabrasion behaviour of sintered unalloyed iron is investigated. Plasma nitriding was carried using two different sets of operative parameters in order to produce microstructures composed of different dominants iron nitrides, e.g.Fe4N (y´) and Fe2–3N(e), phases. Microabrasive wear tests were carried out in a 'free ball' microabrasion tester using SiC slurries. The tribological parameters were kept constant during the tests. The microstructures constituted of e-(Fe2–3N) phase presented a superior abrasion resistance.

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.

A moldagem de pós por injeção é um processo de fabricação de elevada produtividade que possibilita obter componentes de geometria complexa, estreita precisão dimensional e boas propriedades mecânicas. Neste processo, uma mistura de uma determinada quantidade de pós e ligantes orgânicos (polímeros, ceras e óleos) é obtida por meio de uma massa de injeção (feedstock) o qual tem características reológicas adequadas para promover a injeção desta massa em uma cavidade de um molde. A produção de ligas de níquel por meio deste processo é uma alternativa para produção de produtos que requerem aplicações avançadas onde se exige resistência a corrosão e oxidação, resistência mecânica a altas temperaturas e baixo coeficiente de atrito. Neste trabalho apresentamos um estudo das propriedades microestruturais e mecânicas de uma liga de níquel (Ni-Fe-Cr-P) processada via moldagem de pós por injeção, utilizando pós de níquel carbonila com e sem a presença de fase líquida durante a sinterização. Os resultados foram comparados com a mesma liga processada por compactação de pós. Os resultados demonstraram a necessidade de maior quantidade de matéria orgânica para o desenvolvimento da massa de injeção (feedstock: 15% m/m de polímero) para os tipos de pós metálicos utilizados (níquel carbonila do tipo INCO 123) se comparado ao feedstock de ligas comerciais que normalmente utilizam uma quantidade menor de matéria orgânica (feedstock: 9% m/m de polímero). A maior quantidade de matéria orgânica necessária para a preparação do feedstock deve-se a morfologia dos pós empregados (superficie rugosa - tipo spiky) que promove retenção de carbono durante o processo de extração, ocasionando a necessidade de otimização do ciclo de extração térmica e sinterização. Ciclos mais lentos e a baixa temperatura promoveram a total retirada dos ligantes. A liga de Ni-Fe-Cr-P injetada apresentou contração de aproximadamente 50%, além de elevado teor de poros quando comparado ao material compactado, o que influenciou as propriedades mecânicas e dureza aparente do material. The powder injection molding is a manufacturing process that allows high productivity to obtain complex geometry components, dimensional accuracy and good mechanical properties. In this process, a mixture of a quantity of powders and organic binders (polymers, waxes, oils) is obtained through injection of a mass (feedstock) which has rheological properties suitable for promoting the injection of this mass in a cavity of a mold. The production of nickel alloy by this process is an alternative to production of products that require advanced applications, which require resistance to corrosion and oxidation, mechanical strength at high temperatures and low coefficient of friction. This paper we present the study of the microstructural and mechanical properties of a nickel alloy (Ni-Fe-Cr-P) processed by powder injection molding, using carbonyl nickel powders with and without the presence of liquid phase during sintering. The results are compared with the alloy processed by powder compaction. The results demonstrate the need for increased amount of organic matter for developing the injection mass (feedstock: 15 wt.% polymer) for the types of metallic powders used (nickel INCO type 123 carbonyl) compared to commercial alloy feedstock typically use a smaller amount of organic matter (feedstock: 9 wt.% polymer). The largest quantity of organic matter needed for the preparation of the feedstock due to the morphology of the powders used (spiky) which promoted carbon retention during the extraction process, resulting in the need to optimize the extraction cycle and thermal sintering. Slower cycles and low temperature promoted the complete extraction of the ligands. The Ni-Fe-Cr-P alloy injected showed shrinkage of approximately 50%, and high levels of pores as compared to the compacted material, which influenced the mechanical properties and apparent hardness of the material.

Solid lubrication and solid lubricants are one of the most promising choices for controlling friction and wear in energy efficient modern systems. 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 ≤ 20μm) 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 sintering temperature on the tribolayer durability and average friction coefficient in the lubricious regime (μ

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 ...