Sintered self-lubricating components may present inappropriate mechanical properties despite thei... more Sintered self-lubricating components may present inappropriate mechanical properties despite their excellent tribological properties. In general, alloying elements are used to improve these properties, but with a cost increase. As an alternative, surface enrichment (or surface alloying) with alloying elements may be applied. This study developed and characterized sintered composite materials surface-enriched with nickel or molybdenum. The results showed that the surface enrichment process is useful for increasing the tribomechanical properties. The Mo-enriched samples presented superior tribological results. Compared with the reference samples (not enriched), the Mo-enriched specimens showed an increase of 4,954% in scuffing resistance, lower friction coefficient (0.09), and reduced wear rate (68% and 96% lower for the specimen and the counter body). These results were mainly attributed to microstructural modification.
Journal of Materials Engineering and Performance, 2020
In this investigation, the effect of plasma treatments (molybdenum surface enrichment + plasma ca... more In this investigation, the effect of plasma treatments (molybdenum surface enrichment + plasma carburizing) on microstructural and mechanical properties of sintered iron was investigated. The plasma surface enrichment was performed using a molybdenum cathode. Subsequently, the specimens were plasma carburized. To assess the tribological behavior, reciprocating dry sliding wear tests was performed using a ball-on-flat configuration. There was little variation in the surface morphology of the plasma-carburized sintered iron when compared to the plain sintered iron, whereas for Mo-enriched specimens, in particular FeMoC, large b-Mo 2 C and n-Fe 2 MoC particles were identified. The surface topography was modified accordingly. Indeed, average quadratic roughness varied order of magnitude, and the skewness moved to the positive value (Ssk > 0; predominance of picks) for the FeMoC samples. There was a close correlation between the specimenÕs wear rate and subsurface hardness. In fact, the harder samples (FeMoC) that presented surface hardness about 4 times greater than the softer ones (Fe) also showed a reduction in the wear rate around 4 times as well as inducing more considerable wear of the counterbodies. The friction, in turn, was little affected by the presence of surface layers, presenting slightly lower values for the cemented layers. The tribolayers developed in all tested samples were characterized as transformed structures consisting of repeatedly deformed, comminuted, oxidized, agglomerated, and compacted wear particles. The subsurface hardness was the determining property to obtain the lowest wear rate, regardless of the initial roughness of the surface.
Effect of Liquid Phase during Sintering on Mechanical and Tribological Properties of Self-Lubricating Composites
Materials Science Forum, 2017
The present work aimed to contribute to the development of high performance self-lubricating sint... more The present work aimed to contribute to the development of high performance self-lubricating sintered composites, with low friction coefficient and high mechanical strength. Self-lubricating composites presenting embedded solid lubricants in a ferrous matrix were produced. Hexagonal boron nitride (hBN) and graphite were the solid lubricants powders added during the mixing step. The composites were processed by conventional powder metallurgy. The liquid phase sintering, by adding copper, improved the degree of continuity of the matrix by rearranging the solid lubricant particles. With this, besides the hardening effect on the matrix, the mechanical properties of the composites were improved, with tensile strength increasing when compared to the same composite without copper. By using the proposed methodologies, optimized composites presenting friction coefficient of 0.12, tensile strength of 500 MPa and scuffing resistance of 29300 N.m were obtained.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Influence of post-sintering sizing process on the tribological behaviour of self-lubricating iron-based composite
Wear, 2022
Tribologia Engenharia De Superfície: Avanços Recentes
Proceedings of the 2nd (ICAIC) International Conference for Academia and Industry Co-operation & 2nd (IMMSEM) International Meeting in Materials Science and Engineering of Maranhão, 2021
Amostras de ferro puro sinterizadas foram enriquecidas superficialmente com molibdênio e em segui... more Amostras de ferro puro sinterizadas foram enriquecidas superficialmente com molibdênio e em seguida foram cementadas. Todos os tratamentos térmicos foram realizados utilizando descarga luminescente anormal. Durante o processo de sinterização e de enriquecimento superficial as amostras são colocadas sobre o ânodo da descarga, na configuração cátodo-ânodo confinado. O bombardeamento da superfície do cátodo por espécies energéticas produz a pulverização de átomos do cátodo que se depositam na superfície da amostra e se difundem até certa profundidade. Foi observado que a espessura da camada superficial enriquecida está relacionada à energia de bombardeamento das espécies. Durante o processo de cementação, a presença de Mo na região superficial favorece a estabilização da fase α-Fe alterando a cinética de precipitação da cementita nessa região. A cementação das amostras enriquecidas com molibdênio elevou os valores de dureza obtidos para a região superficial.
Modificação da composição química da superfície de componentes metálicos via pulverização catódica em plasma: projeto de equipamento e desenvolvimento de processo
Traitement et réacteur à plasma pour traiter des pièces métalliques
L'invention porte sur un reacteur a plasma (10) qui definit une chambre de reaction (23) comp... more L'invention porte sur un reacteur a plasma (10) qui definit une chambre de reaction (23) comprenant un support (30) pour les pieces metalliques (1) et un systeme anode-cathode (40), et un moyen de chauffage (70) est monte a l'exterieur dudit reacteur a plasma (10). Le traitement par plasma, pour une operation de nettoyage, consiste a connecter le support (30) a l'anode mise a la masse et la cathode a un potentiel negatif d'une source d'alimentation (50) ; amener une charge gazeuse ionisable dans la chambre de reaction (23) et chauffer cette derniere a des temperatures de vaporisation de contaminants de piece ; appliquer une decharge electrique a la cathode ; et permettre l'evacuation de la charge gazeuse et des contaminants. Un traitement thermique subsequent consiste a : inverser la polarite d'excitation du systeme anode-cathode (40) ; amener une nouvelle charge gazeuse dans la chambre de reaction (23) et maintenir celle-ci chauffee ; appliquer une decha...
Composition métallurgique de matériaux particulaires, produit fritté autolubrifiant et procédés permettant d'obtenir des produits frittés autolubrifiants
La composition metallurgique selon l'invention comprend un materiau metallique particulaire p... more La composition metallurgique selon l'invention comprend un materiau metallique particulaire principal, du fer ou du nickel par exemple, et au moins un element en alliage pour durcir le materiau metallique principal, qui forment une matrice structurelle (10); un lubrifiant solide particulaire (20), comme du graphite, du nitrure de bore hexagonal ou un melange de ceux-ci; et un element d'alliage particulaire qui est apte a former, durant le frittage de la composition qui est realise selon un procede de compaction ou de moulage par injection, une phase liquide, d'ou l'agglomeration du lubrifiant solide (20) en particules discretes. La composition peut comprendre un element d'alliage pour stabiliser la phase matricielle alpha-fer durant le frittage, afin de prevenir la solubilisation du lubrifiant solide au graphite dans le fer. La presente invention concerne egalement un produit fritte autolubrifiant obtenu a partir de la composition, ainsi qu'un procede permett...
Procédé plasma et réacteur pour le traitement thermochimique de la surface des pièces métalliques
Cette invention concerne un reacteur (R) comprenant une chambre de reaction (RC) pourvue d'un... more Cette invention concerne un reacteur (R) comprenant une chambre de reaction (RC) pourvue d'un support (S) pour les pieces metalliques (1), d'un systeme d'anode (2), relie a la terre (2b), et d'un systeme de cathode (3) relie au support (S) et a une alimentation CC en mode pulse (10). Dans la chambre de reaction (RC), qui est chauffee et alimentee en gaz, un plasma gazeux se forme sous l'effet de la decharge electrique appliquee a la cathode (3). Un precurseur liquide ou gazeux est admis dans au moins une chambre de craquage tubulaire (20) associee a une source d'energie haute tension (30). Le reacteur peut en outre comprendre au moins une chambre de pulverisation tubulaire (40) associee a une alimentation electrique (50) et destinee a recevoir un precurseur solide. Une difference de potentiel est appliquee entre l'anode (2) et l'une et/ou l'autre desdites chambres tubulaires (20, 40), afin de liberer les elements d'alliage destines a a etre bo...
Solid lubrication in fluid film lubrication
Lubrication Science, 2018
Study of silicon carbide dissociation into Fe and Fe C matrixes produced by die pressing and sintering
Materials Chemistry and Physics, 2020
Abstract During the sintering process of self-lubricating steels, the dissociation of Silicon Car... more Abstract During the sintering process of self-lubricating steels, the dissociation of Silicon Carbide (SiC) in the iron matrix forms turbostratic graphite nodules which provide the lubricating properties of these materials. Previous works have explored the turbostratic nature of the graphite nodules and the influence of the SiC content in the microstructure and tribological properties of these materials, however, the thermodynamics and kinetics of SiC dissociation have not been fully explored yet. This study uses the versatility of die pressing to study the influence of particle sizes, sintering temperature and carbon content in the dissociation of SiC. The resulting materials were analysed by optical microscopy and scanning electron microscopy (SEM). The evolution of the size and morphology of pores and graphite nodules was investigated through image analysis software and simulations with the DICTRA® software were used to a better assessment of the kinetical aspects of SiC dissociation. Also, the thermodynamic influence of the particle size in the equilibria of the Fe–SiC system is discussed. Results indicate that SiC particle size rather than Fe/SiC size ratio governs the dissociation process, sintering temperature causes coalescence and rounding of pores as well as of graphite nodules. In addition, excessive activity of carbon in the system causes the precipitation of graphite flakes, which are not desired for technological applications.
Magnetic properties optimization of an iron-based soft magnetic composite coated by nano-ZnO and boron oxide
Journal of Magnetism and Magnetic Materials, 2021
Abstract Double-layered soft magnetic composite (SMC) based on pure iron powder coated by a first... more Abstract Double-layered soft magnetic composite (SMC) based on pure iron powder coated by a first layer of zinc oxide nanoparticles (nano-ZnO) and a second layer of boron oxide (B2O3) has demonstrated superior magnetic performance when compared to SMCs prepared with only one of these insulating compounds. The investigation reported in this manuscript focused on improving the properties of such double-layered SMC even further by finding optimal processing conditions through a Response Surface Model evaluation using a central composite design of experiments. Mixing time of iron powder with nano-ZnO suspension, mass fraction of boron oxide precursor (boric acid - H3BO3), and heat treatment maximum temperature were investigated to achieve the condition of minimum total losses in frequencies up to 1 kHz. The discussion on the total losses is accompanied by the study of static and dynamic losses coefficients, relative magnetic permeability, electrical resistivity, and electronic microscopy of the samples. While the optimal mixing time was observed to be that of 1 h regardless of the intended operation condition, the heat treatment temperature and H3BO3 mass fraction proved to be sensible factors in order to optimize the losses for distinct levels of frequency and magnetic induction.
The objective of the present work was to study the effect of heat treatments in the microstructur... more The objective of the present work was to study the effect of heat treatments in the microstructure, graphite nodules and mechanical properties of self-lubricating steels, to achieve this, self-lubricating steels (Fe + 0.45C + 4Ni + 1Mo % wt) and additions of 2 and 3 % wt SiC were fabricated. They were consequently heat treated in 3 different conditions: martempering at 180 °C and tempering at 530 °C and 300 °C respectively and austempering at 300 °C. Hardness, yield strength, tensile strength and work hardening behavior were studied in as-sintered and heat-treated samples. The microstructure was analyzed by optical microscopy, scanning electron microscopy, Raman spectroscopy and microhardness. The transformation temperatures were determined using dilatometric tests. Results show that the presence of dissolved Si in the matrix due to SiC dissociation notably affects the morphology of the microstructure and transformation temperatures also affecting post heat treatment mechanical properties. The structure of graphite nodules produced by SiC dissociation is nott significantly affected by the heat treatments.
Tribological Behavior of Surfaces Obtained by Turning in Sintered Self-Lubricating Composites
Tribology Transactions, 2020
Abstract This work presents a study on the tribological behavior of surfaces obtained by turning ... more Abstract This work presents a study on the tribological behavior of surfaces obtained by turning in sintered self-lubricating composites. Turned surfaces were obtained at constant cutting speed (vc = 100 m/min), feed (f = 0.2 mm), and depth of cut (ap = 1 mm). The tested composites have solid lubricants (graphite and hexagonal boron nitride, h-BN) mixed in an Fe-C-Ni-Si matrix manufactured by single pressing (SP) and double pressing (DP). The turned and sintered surfaces were analyzed by scanning electron microscopy (SEM) and quantified by the roughness parameters Sq (root mean square height), Ssk (skewness), Sbi (bearing surface index), and Str (texture aspect ratio). The tribological tests were performed on turned and sintered surfaces with a cylinder–cylinder configuration. Raman spectroscopy and SEM were used to characterize the wear scars. Machining reduced the Sq parameter by 35 and 45% for the SP and DP materials, respectively, and the Ssk by 100%. The turned surfaces did not present friction coefficient values within the lubricity limit (µ < 0.2). The friction coefficient and the wear rate of the turned surfaces were around 320 and 40% higher, respectively, than those of the sintered surfaces.
Quando processos de engenharia de superfícies multifuncionais que combinam fases de propósito ori... more Quando processos de engenharia de superfícies multifuncionais que combinam fases de propósito orientadas são aplicados a substratos moles, uma combinação de alta resistência ao desgaste, suporte de alta carga e baixos coeficientes de atrito podem ser obtidos. Neste estudo, os efeitos de diferentes camadas nitretadas no comportamento tribológico de revestimento Diamond-Like-Carbon (DLC) depositado sobre aço SAE 1040 são investigados. A nitretação foi conduzida sob diferentes temperaturas e misturas de gases para criar três camadas de nitretos distintas: duas camadas de compostos com predominância de fases ε e γ' e uma camada de difusão. Todas as superfícies foram então revestidas com DLC, depositado via Plasma-Enhanced-Chemical-Vapour-Deposition (PACVD). As fases de nitreto foram analisadas utilizando difração de raios-X e a topografia da superfície foi analisada por interferometria de luz branca e microscopia eletrônica de varredura. O comportamento tribológico foi investigado utilizando esfera e plano com movimento alternado com carregamento incremental até a falha do filme DLC. Os testes tribológicos indicaram que o melhor desempenho foi alcançado por uma específica combinação de dureza, rugosidade superficial e tipo de nitreto. A melhor capacidade de mancalização entre o revestimento DLC e o substrato mole foi alcançada quando a camada de nitretos constitui-se apenas de uma camada de difusão.
In order to better understand the tribological behavior of self-lubricating materials, Fe-Si-C ma... more 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.
Improvement of tribological properties of sintered self-lubricating composites produced by surface Mo-enrichment
Wear, 2019
Abstract In powder metallurgy, a high-cost method that is widely used to increase the useful life... more Abstract In powder metallurgy, a high-cost method that is widely used to increase the useful life of the mechanical components is the addition of alloying elements. A less-exploited process is surface enrichment by plasma, where the same result is obtained only on the surface of the component at a rather lower cost. This paper reports on the improvement of the tribological properties of powder injection molding (PIM) self-lubricating composites produced by surface Mo-enrichment. The tribological properties were evaluated in terms of the scuffing resistance, friction coefficient, and wear rate values of enriched and non-enriched specimens, and counter-bodies. Scanning electron microscopy with energy dispersive X-ray spectroscopy and μRaman spectroscopy were used to characterize the wear scars. The results showed that Mo enrichment increased the scuffing resistance by an impressive 2000%, with a 90% decrease in the wear rate of the specimens and counter-bodies. These results were ascribed to several factors, including the microstructural modification, hardness increase, and tribolayer formation.
Effect of Liquid Phase Assisted Sintering on the Microstructure, Mechanical Properties and Tribological Behavior of Self‐Lubricating Ferrous Composites
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