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The present work aims to explore the tribological behavior of the laser texturing process with different patterns on a Co based alloy using a pulsed Nd: YAG laser. Different parameters such as peak power, speed and spot diameter of the laser were explored for the experimental setting. The microstructural analysis was performed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nanoindentation tests. The influence of the different textured patterns of the tribological performance tested with a pin-on-disc tribometer under lubricated sliding condition was evaluated. The results showed that typical interdendritic structures in the as-cast CoCr alloy condition were refined due to the heat input and fast cooling rate during the laser treatment. The refined microstructure showed less volumetric loss resulting in a increment of wear resistance and a better tribological performance than as-cast alloy. The correlation among laser parameters, microstructural effect and their influence in wear resistance is discussed.

Graphene oxide-Co (GO-Co) composite coatings containing reduced graphene oxides were grown on type 304 stainless steel at 1000 °C, by treatment for 60 min in a tube furnace under an Ar flow of 350 mL/min. Raman spectroscopy showed that the coatings mainly comprised graphene oxides as graphene and reduced graphene oxides (GO and rGO). X-ray photoelectron spectroscopy (XPS) analysis identified the band energies of the C O and C O bonds, as well as the presence of GO, CoFe2O4, and Co2O3. Electron backscattered diffraction showed a refined composite coating and a maximum wear resistance of 0.12 mm3 under a load of 6 N due to auto-lubrication. This work is of great interest for industries utilizing machinery and equipment exposed to wear conditions in the absence of lubricants.

Electrostatically deposited polyester resin powder coatings have been extensively used for painting in industrial applications. Furthermore, protective coatings are used to prevent the deleterious effects on the substrate in varying environmental conditions. The present study investigated the tribological behavior of polyester resin coatings containing three different amounts of added graphene oxide (GO): 100, 200, and 300 mg/kg, which were electrostatically deposited on steel sheets. Polyester resin coating without GO was used as control. Coatings were characterized using optical microscopy, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, spectrophotometry, and nanoindentation testing. Additionally, dry contact pin-on-disc testing was used to evaluate the tribological behavior of the polyester resin coatings. The results indicated that graphene nanoparticles were uniformly distributed throughout the electrostatically deposited coatings after the thermal polymerization process. Optical spectroscopy results indicated minor variations in reflectance and slight changes in color of the analyzed samples. Tribological tests indicated that when the amount of GO incorporated into polyester resin increased, the wear values and coefficients of friction of the coatings significantly decreased. These results demonstrated the beneficial effect of the self-lubricating properties of GO on improving the resistance of the coatings.

In the present work, Ni-based metallic filler powders reinforced with TiN or AlTiN nanoparticles were deposited on D2-type tool steel by Plasma Transferred Arc (PTA). The mixes of TiN or AlTiN with Ni-based metallic filler powders were analyzed using technique of differential scanning calorimeter (DSC). The effect of tribological performance for Ni-based metallic filler powders with different amounts of TiN or AlTiN nanoparticles was studied. A pin on disc tribometer was used to evaluate the wear and friction behavior of the hardfacing under dry siding condition. The hardfacing were characterized by a scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), roughness and nanoindentation tests. Results of DSC showed that the mixes of nanoparticles with metallic filler changed the dilution due to the high enthalpies of reaction. Microstructural results showed that the addition of TiN or AlTiN nanoparticles modified substantially the microstructure of the hardfacing, increasing the secondary hard phases and intermetallic content as well as the nanohardness. Moreover, as the TiN or AlTiN nanoparticles increased from 1 to 2 g and 2.4–3.4 g, the wear resistance of hardfacing increased four times that the D2 steel.

"En este estudio se llevó a cabo el crecimiento de recubrimientos ricos en Ni por el método Pechini sobre fracturas de acero inoxidable 304, para sanar superficies de fractura de piezas metálicas. Una serie de pruebas se llevaron a cabo para establecer la temperatura de calcinación por calorimetría de barrido diferencial (DSC) a 1300°C por 10°C/min en mezclas de (CH3COO)2Ni•4H2O (acetato de níquel tetrahidratado) con HOC(COOH)(CH2COOH)2•H2O (ácido cítrico monohidratado) y precursores: HOCH2CHOHCH2OH (glicerol) y HOCH2CH2OH (etilenglicol). Los resultados mostraron que el uso de Etilenglicol es mejor que el Glicerol debido a que muestra una estabilidad térmica a menor temperatura para la calcinación. Posteriormente, fracturas cilíndricas de 0.6 x 1 cm de acero inoxidable 304 se sumergieron en una solución con Etilenglicol y, se gelaron en una mufla a 110°C por 24 h. Adicionalmente, las muestras se calcinaron a 660°C por 60 min bajo un flujo de 200 ml/ min de Ar, a velocidad de calentamiento/enfriamiento de 5°C/min para sintetizar las nanopartículas de Ni sobre las fracturas. El crecimiento del recubrimiento sobre las fracturas se llevó a cabo en un flujo de Ar de 220 ml/min a 1100°C por 60 min a una velocidad de calentamiento/enfriamiento de 10°C/min. Mediante microscopía óptica y de barrido, se observó que el recubrimiento presenta un espesor de hasta 700 μm con una serie de precipitados cuboidales mayores a 1 μm, así como fases laminares ricos en Ni, Fe y Cr."

Pulsed plasma nitriding and post-oxidizing process have been applied to hot work H13 tool steel to enhance the tribological properties (friction coefficient and wear rate). Nitriding was accomplished under specific conditions to generate a free white layer surface in order to avoid an abrasive wear mechanism. Post-oxidizing treatment was carried out in the same reactor after finishing the nitriding treatment; processing time was varied for 30 and 60 min. The morphology, phase’s composition and wear performance of duplex-treated samples were evaluated by scanning electron microscopy, x-ray diffraction analysis and pin-on-ball wear technique. The results show that the duplex treatment produces a bilayer arrangement constituted by an 80 μm diffusion zone with expanded martensite as the main phase underneath a 2–4 μm hematite–magnetite-oxidized layer. The duplex treatment modified the main wear mechanism of the nitrided sample from abrasive to plastic yielding. The changes in wear mechanisms resulted in a noticeable decrease, about 40%, in friction coefficient for oxidized samples in comparison with the nitrided-only sample. It was also established that the lowest friction coefficient values can be obtained when hematite is the main phase in the oxidized layer.

The longevity of metal-on-polyethylene (MoP) joint replacements, in which a polished CoCr component articulates with a polyethylene liner, may be restricted by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. Recently, laser surface texturing (LST) has emerged as an effective method to improve the tribological performance of lubricated friction pairs. The present work reports a microstructural and tribological study of surface microtextured CoCr alloy discs, modified by the LST method using a pulsed Nd:YAG laser, tested against Ultra High Molecular Weight Polyethylene (UHMWPE) cylindrical pins. Four different texturing patterns varying laser parameters such as peak power, pulse width, repetition rate and travel speed were investigated. An untextured set of CoCr alloy discs was used as reference. The microstructure and mechanical properties of the microtextured CoCr alloy discs were investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, atomic force microscopy, profilometry and nanoindentation test. The coefficient of friction and wear of the UHMWPE pins were determined by means of a pin-on-disc tribometer under lubricated sliding conditions. The microstructural analysis on the laser microtextured CoCr alloy revealed a grain refinement of secondary phases with absence of typical carbides resulting in an increased nanohardness. In addition, all texturing patterns on the CoCr alloy discs promoted a reduction on the coefficient of friction, compared against untextured CoCr alloy discs. Furthermore, it was found that UHMWPE wear was reduced when articulating against dimple textured CoCr alloy discs.

Two metal fillers with TiC nanoparticles (TiC NPs) of less than 100 nm for the overlay process is an alternative to hardfacing for treating surfaces subjected to severe wear. In this work, the effect of tribological behavior for TiC NPs addition on two Co-based filler materials, as well as the dilutions, was studied. Mixtures of Co-based filler metals without and with 0.5% and 2% TiC NPs were deposited onto D2 steel plates using PTA (Plasma Transferred Arc). The BET surface area was 0.17 m2 g-−1 and 0.31 m2 g−1, respectively, for Stellite 6 and 12. The distribution of ca 23% macroporous for Stellite 6 was sufficient to get inside the TiC NPs, as well as in the case of Stellite 12, with a pore distribution of ca 13%. Stellite 12 has an increase in the dilutions (70%) and enthalpies showed endothermic reactions. Stellite 6 with NPs was determined to be most effective in increasing the wear resistance.

The novel filler metals of cobalt-based alloys reinforced with titanium carbide nanoparticles (TiC-NPs) were used for the fabrication of plasma transferred arc hardfacing coatings. The effect of tribological behavior for TiC-NPs addition on two Co-based filler metals (Stellite 6 and Stellite 12), as well as the dilutions, was studied. Mixtures of Co-based filler metals without and with 0.5% and 2% TiC-NPs were deposited onto D2 steel plates. Stellite 12 had an increase in the dilutions (70%) and enthalpies due to a major surface energy and endothermic reactions. The results of DSC (Differential Scanning Calorimeter) in the filler metals with TiC-NPs showed a shell of nanowhiskers on the sintered surface, which were observed and chemically analyzed via SEM (Scanning Electron Microscope) and EDS (Energy Dispersive Spectroscopy). Stellite 6 with 2% TiC-NPs was the most effective in increasing the wear resistance. These outcomes might be of interest for mining industries, where machinery and equipment are exposed to extreme wear conditions.

Mixtures of Ni-based filler metal without and with 0.5, 1, and 2% WC nanoparticles (NPs) were methodologically tested in order to improve the wear behaviour of WC/Ni-based overlays deposited on low carbon steel by the plasma transferred arc (PTA) process. On adding 2% WC NPs, the longitudinal direction overlay microstructure was modified to have a fibrous appearance. The mechanism to improve WC particle distribution and thus prevent microcrack propagation in the overlays implies a liquid-phase viscosity change. Results of pin-on-disk tests in the overlay using filler metal with 2% WC NPs show that the combined effect of fibrous microstructure and W-rich phases in the overlay, decreases the volume loss by 76% and 78% in comparison with overlays without WC NPs for a 1 and 5 N load, respectively. These outcomes might be of interest for the mining industry, where machinery and equipment are exposed to extreme wear conditions.

In the present study, the properties of thin coatings deposited on biocompatible 316L steel to improve the wear resistance were investigated. A thin Ti nanolayer of thickness 400 nm was deposited by thermal evaporation (sputtering), and the Ti-coated steel was subjected to plasma oxidation treatment for different times. All the samples were characterized using metallographic techniques, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), and roughness and nanohardness tests. A pin-on-disc tribometer was used to evaluate the wear resistance of the coatings under lubricated sliding condition. The results showed that the TiO 2 film is formed as a function of thermal oxidation time. The coating had a beneficial effect on the wear resistance depending on the roughness. Other coating characteristics such as topology of surface modified by TiO 2 diffusion and nanohardness were assessed.

In order to improve the tribological behavior of austenitic stainless steel, a novel composite coating based on reduced graphene oxide-Ni (rGO-Ni) is presented. These coatings were prepared by sol–gel using a mixture of Ni-rich xerogel films and reduced graphene oxide (rGO), with a heat treatment at 1000 °C for 1 h under an Ar flow. Raman spectroscopy confirmed that the rGO-Ni coating was formed. The rGO-Ni coating demonstrated an unusual surface topography, combined with multiple lamellar carbon growth and refined grains characterized by automatic crystal orientation mapping as determined through electron backscattered diffraction (EBSD). The rGO-Ni-composite coating exhibited a high elastic behavior from a multi-step nanoindentation with a depth of 900 nm and wear loss of ~ 0.05 to 0.3 mm3 at 1 to 5 N. It was found that the increase on wear resistance was due to both the self-lubrication properties of the rGO and the harness of refined grains on the coating.

Tungsten nanoparticles of 80 nm average particle size were utilized in the brazing of 304 stainless-steels. The nanoparticles were characterized by DTA and TEM, and the brazed samples were evaluated by SEM and Vickers microhardness tests. The interaction of the tungsten nanoparticles with the metallic filler in the melting zone modified the size and morphology of the formed phases into a finer and uniformly distributed microstructure. In samples treated at 1200 °C for 60 min, the microhardness decreased from 310 to 170 HV, being the latter value, close to that of the base metal. The nanoparticles and the microcracks develop a synergistic effect when they are in contact with the liquid phase in such a way that a rise in the threshold capillary-pressure leads to the filling of the interstices. The capillary-like system resulting from the wettability of the nanoparticles and microcrack surfaces by the liquid phase, leads to a solidified microstructure with fine and uniform phase distribution.

Transient liquid phase (TLP) bonding of 304 stainless steel with nickel based filler metal, BNi-9, was performed to study the influence of silicon nanoparticles (NPs) on the mechanical and structural properties of the bonding area. It was found that silicon NPs act as a melting point depressant in the brazing process; the formation of silicon TLP induces the dissolution of elements of the metal filler and promotes a uniform distribution in the bonding area. Silicon NPs induce the development of smaller eutectic structures in the melting zone; it has been related to microhardness measurements, which are lower when the silicon NPs are used in the brazing process.

Fractures in blade sections of Inconel 725 were impregnated with tungsten nanoparticles and jointed by the brazing process. In order to evaluate their effect over the microstructure, aging thermal treatments at 750°C for 2, 6, 10, and 14 h were done. BNi-9 was selected as brazing filler metal and was characterized by scanning electron microscopy and X-ray fluorescence. Before brazing, the fractures were impregnated with a mixture of tungsten NPs in ethanol. Measurements of Vickers microhardness showed an increase in the melting zone of samples with aging thermal treatment for 14 h, which is attributed to the precipitation of theγ′ phase with a typical size ofca. 100 nm. Likewise, the tungsten NPs modified the size and morphology of Cr-Ni eutectics into finer and uniformly distributed microstructures.

Silicon nanoparticles of 100 nm obtained by high-energy ball milling were characterized by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). Results show dark areas due to a staking of defects. On the other hand, brighter areas exhibit a combination of small crystalline and amorphous zones. To fulfill and cover the micro-cracking and micro-pores generated during the welding process of 304 stainless steels joined by brazing, these nanoparticles were deposited directly in the fracture. The amorphous silicon drove the Transient Liquid Phase (TLP) at 1000°C for 20 min. This amorphous silicon decreases the energies of reaction between the substrate and melting filler. TLP increases the wettability and capillary forces between micro-cracking and micro-pores; due to that, the eutectic phase contained by the melting filler forms a liquid. Moreover, the weld beads were characterized by Scanning Electron Microscopy (SEM) to analyze the effect of silicon nanoparticles on the weld beads. These results showed that the interaction of the Si nanoparticles with metallic filler in the melting zone decreases the size and change the morphology of the present phases as well as the zone of isothermic growth.

In order to eliminate magnesium from an A 380 Al-Si alloy at 750°C, the submerged powder injection method, using an inert carrier gas (Ar), was applied. The injected powders in the liquid aluminum bath were zeolite, silica and mixtures of zeolite-silica minerals. For each experiment the response variables were: eliminated magnesium versus injection time and quantity of drosses produced. Chemical analysis by atomic absorption spectrometry showed that mixtures of silica-zeolite 66:34 wt% have the best results with regarding to the removal magnesium from 1 to 0.0066 wt%. During the elimination of magnesium complex stoichiometry compounds were formed due to the reactions among zeolite, water steam and liquid aluminum. These compounds were analyzed by XRD, SEM and TEM. The results obtained, along with using the FactSage 6 thermodynamic software, allowed to elucidate the reaction mechanism between the minerals used and liquid aluminum.Se empleó el método de inyección sumergida de polvos por medio de un gas de arrastre inerte (Ar) con el fin de eliminar el magnesio de la aleación Al-Si A380 a 750 °C. Los polvos inyectados al baño de metal fundido fueron zeolita mineral, arena sílice y mezclas de ambas. Las variables de respuesta medidas fueron el contenido de magnesio en el baño metálico respecto al tiempo de inyección y las mermas de metal al final de cada experimento. En el análisis de resultados, la mezcla sílice:zeolita 66:34 % e.p. obtuvo la mayor eficiencia, lográndose una disminución en el contenido de magnesio en el baño metálico de 1 a 0.0066 % e.p. Los productos de reacción se analizaron por difracción de rayos-X, microscopía electrónica de barrido y de transmisión. Los resultados de estos análisis y el empleo del paquete termodinámico FactSage, versión 6, permitieron justificar el mecanismo de reacción entre los minerales y el aluminio líquido.

A study of magnesium removal from an aluminum base alloy using the technique of submerged injection of solid reagents with zeolite as the oxidizing solid agent is presented. The effects of the zeolite water content, process temperature, injection rate and particle size on the magnesium removal rate were studied using a factorial experimental design. A comparison between the magnesium removal efficiencies obtained when using silica and zeolite was established. After studying the importance of each variable, a secondary optimization study was performed using a surface response methodology. Experimental conditions with the strongest effect were temperature of the molten alloy and zeolite water content; the optimal conditions were a temperature ranging from 750 to 800°C and a water content ranging from 5 to 5.8 wt%. It was verified that zeolite is a better magnesium removal agent than silica.

In order to improve the Mg removal from an A-380 molten alloy, mixtures of zeolite and SiO2nanoparticles (SiO2(NPs)) were tested. Zeolite was enriched with 2.5, 5, 7.5, 10, or 12.5 wt-% of amorphousSiO2(NPs). TheSiO2(NPs)and zeolite were mixed for 30 min in ethanol for each experiment and then dried in a furnace at 80°C for 12 h. The enriched zeolites were analyzed by scanning electron microscopy, transmission electron microscopy, and N2gas adsorption analysis. The Mg removal was carried out injecting each mixture into the molten aluminum alloy at 750°C using argon. The Mg content of the molten alloy was measured after different periods of the injection time. Zeolites enriched with 2.5 and 5 wt-% ofSiO2(NPs)were demonstrated to be the better mixtures, removing Mg from an initial content of 1.6 to a final content of 0.0002 and 0.0101 wt-%, respectively, in 45 min of injection.

In order to increase the wettability and capillary forces of the filler metal between micro-cracking and micro-porous on the fracture surfaces of 304 stainless steels, methods of impregnation of Si and growth of Ni nanoparticles were used. These nanoparticles have a role inside the Transient Liquid Phase (TLP) and the substrate when using Brazing process. TLP can react with the nanoparticles previously deposited between micro-cracking and micro-porous and therefore promotes the nucleation and growth sites of phases and decreases the formation of eutectic structures. This method increases the effectiveness of metallic components reparation using Brazing process. Such effectiveness is indicated by an inspection of microstructural failure analysis, as a first stage, in the covered zone by the filler metal.