Search

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.

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.

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.