PVD CrN coatings are extensively used to improve the wear resistance of medium-alloy steels. A reliable assessment of their industrial performance requires comparative analysis of sliding conditions and investigation of the role of substrate pre-treatments. The main goals of this work were to study the effect of plasma nitriding and in situ surface cleaning methods on multilayer Cr/CrN arc-PVD coating adhesion and wear behaviour under unidirectional and reciprocating motion. Nitrided and non-nitrided AISI 4140 steel were used as substrates. Two pre-cleaning methods, Ar + H2 glow discharge and chromium ion etching, were studied. Microstructural characterization was performed using X-ray diffraction, nanoindentation and FIB-SEM. Adhesion was evaluated under static and dynamic loading conditions. Wear performance was assessed using unidirectional pin-on-disk and reciprocating ball-on-flat tests. Results reveal that adhesion is influenced by the pre-cleaning process in the PVD chamber and that the increase of substrate hardness achieved through plasma nitriding doubles the coating's critical load in scratch tests. Under reciprocating sliding at 1.4 GPa, coatings on non-nitrided steel failed after only a few cycles, whereas coatings on nitrided substrates suffered only polishing-like wear. However, in unidirectional tests under a Hertzian pressure of 1.5 GPa, even though coating delamination occurred, prior nitriding of the steel reduced the worn volume. Overall, results demonstrate that choosing the best combination of substrate treatments to achieve good adhesion is crucial to extend the durability of the coatings especially under reciprocating motion and high Hertzian pressures.

Galling is a type of wear that affects the oil and gas industry causing loss of profits due to unexpected stops in the exploration and extraction process. In the present work, the galling resistance of four API grade steels (L80 type 1, T95 type 2, P110, and Q125) used in the industry was evaluated by means of cross-cylinder tests. The surfaces were analyzed, and a Galling Tendency number was computed in order to rank the materials. Additionally, tensile and hardness tests were conducted to analyze the influence of the mechanical properties on galling. It was found that P110 exhibited the worst response and T95 the best one. For materials with the same ductility, an increase in strength is associated with higher galling resistance. Anew index, based on the ductility and yield strength of the material, is proposed to predict the galling performance, demonstrating a strong correlation with the galling tendency.

This study investigates the frictional behavior and wear protection capacity of polyalphaolephin (PAO) oils additivated with combinations of zinc dialkyldithiophosphate (ZDDP), metal sulfides, and carbon nanotubes (CNTs) on steel surfaces. Various oil formulations, comprising PAO base oil with differing proportions of ZDDP, metal sulfides, and CNTs, were utilized to lubricate steel-steel contacts in block-on-ring tests. Both the blocks and rings were made of SAE 52100 bearing steel. The testing conditions selected for all the tests were 1 GPa of Hertzian contact stress, 1 m/s of sliding speed, and a total sliding distance of 3,600 m. Surface analysis was performed by means of SEM-EDS, laser confocal microscopy, and Raman microspectrometry. Results indicated that combining metal sulfides or CNTs with ZDDP notably reduced friction compared to ZDDP-only oil, with reductions ranging from 24 to 60%, depending on the formulation. However, wear rates varied considerably among formulations. Those containing ZDDP and Bi2S3 exhibited significant wear rate increases of 160 to 180% compared to ZDDP-only oil. Optimal wear protection for steel surfaces was achieved with ZDDP + CNTs and ZDDP + MoS2 combinations, resulting in wear rate reductions of 19 to 14% respectively.

Medium alloy steels are used in several components in the industry where wear and corrosion resistance are required. Different treatments can be used to enhance the surface properties. In this work, the tribological and corrosion behavior of the nitrided and post-oxidized AISI 4140 steel was studied. The samples were plasma nitrided in a 25 %/75 % (N-2/H-2) gas mixture at 500 degrees C for 15 h. They were oxidized in the same chamber for 1 h in a water steam atmosphere at 400 degrees C. The microstructure of the nitrided and oxidized layer was analyzed using X-ray diffraction (XRD) and scanning electron microscopy. The pin-on-disk tests were performed according to ASTM G99-17, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus, with a 6-mm diameter alumina ball as counterpart, a sliding distance of 500 m and 1,100 MPa of applied Hertzian pressure. Moreover, reciprocating sliding tests with a stroke length of 5 mm were performed using am AISI 52100 steel ball as a counterpart under a Hertzian pressure of 354 MPa in both dry and lubricated conditions. Salt spray tests following ASTM B117-19, Standard Practice for Operating Salt Spray (Fog) Apparatus, and electrochemical tests in sodium chloride were carried out to evaluate the corrosion behavior. The thickness was 0.5 mu m and 3 mu m for the oxide layer and the nitrided layer, respectively. Magnetite was detected by XRD. In the pin-on-disk tests conducted under high pressure, the nitrided + oxidized and only nitrided samples presented similar wear resistance. However, the oxide layer allowed a reduction in the friction coefficient in the first cycles with respect to the only nitrided sample in the sliding reciprocating test under low pressure. This behavior was observed in both the dry and lubricated conditions, but it was more noticeable in lubricated ones. Regarding the corrosion behavior, the nitrided + oxidized samples showed better corrosion resistance than the other samples in a chloride solution.

Casing wear is a concern among O&G operators worldwide since it can lead to well integrity issues. Wear can appear on both elements, drill pipe and the external casing, resulting in the reduction of the tubular wall thickness affecting its performance. To address the topic, a tribometer was developed based on the standard API STD 7CW (2015), including a rotating element that slides against a fixed element while being exposed to drilling mud, leading to the obtention of coefficients of friction (CoF) and casing wear factors, for different combinations of Oil Country Tubular Goods (OCTG). To estimate CoF and casing wear factors, more than 70 laboratory tests were performed combining steel grades under repetitive and consistent conditions. Contact force was fixed and maintained between both elements during test. CoF were calculated by direct torque measurement, while casing wear factors were indirectly defined by measuring the material loss volume. Results obtained in CoF were in a range of 0.3 and 0.5, being higher than the values in open literature. They also showed a relation between drill element grades and higher values of CoF. Three zones were detected when evaluating CoF results together. Analyzing casing wear factors, the results obtained were in a range from 0.03 to 0.3 (1/psi E-09), this range is slightly lower than public data available. Different testing conditions such as torque and displacement were evaluated to assess the behavior of 28Cr alloy.

Over the past two decades, there has been an increasing adoption of protective and lubricant coatings for their usage in threaded connections in the oil and gas industry to reduce both failed connections due to galling and environmental contamination due to lubricant spillage. In this work, the influence of composition and thickness on the tribological performance of MoS2-epoxy matrix composite coatings in reciprocating block-on-ring tests was studied. Epoxy resins with 2.5, 5, and 10 wt.

Martensitic stainless steels are often used in machine components, where are exposed to different solicitations that require good surface properties. Different treatments such as plasma nitriding or coating deposition could be used to improve their wear and corrosion resistance, even combining both methods. In this work, the tribological behaviour of a TiAlN coating with a top layer of TiN, called ‘Hyperlox Gold’, deposited over both nitrided and non-nitrided martensitic stainless steels by PVD PEMS (Physical Vapour Deposition Plasma Enhanced Magnetron Sputtering) was studied. Quenched and tempered AISI 420 martensitic stainless steel was used as base material. A group of samples were plasma nitrided and were subsequently coated. Microstructure of the nitrided layer and the coating were analysed by SEM and XRD. Nanohardness was measured with a Berkovich tip. Wear behaviour was evaluated using pin-on-disk tests (ASTM G99 standard) under three different loads (5 N, 7 N and 10 N) with an alumina ball as a counterpart. Adhesion was evaluated using dynamic conditions such as variable load scratch test and under static condition with Rockwell indentation tests (using 60 kg, 100 kg, and 150 kg). Overall thickness of the coatings was 3.7 μm and their hardness about of 32 ± 2 GPa. The nitrided layer was about 10 μm thick, with a hardness of 17 ± 1 GPa. The coating had good mechanical resistance in sliding adhesive wear conditions under low loads and good adhesion was revealed in a static condition. The presence of a nitrided layer improved the wear behaviour under high loads and the adhesion in dynamic conditions. Critical load was higher for the duplex sample than the coated samples. This work is important for the development of the Argentinian industry where the use of coatings is not largely extended, especially with martensitic stainless steels as substrates.

The present work investigates the friction and wear properties of composite Bi _2 S _3 –MoS _2 soft coatings under different humidity levels. To achieve this goal, suspensions containing different proportions of Bi _2 S _3 and MoS _2 were sprayed onto polished SAE 1010 steel substrates to generate soft lubricating coatings. The coatings were subjected to reciprocating sliding tribological tests in air at different humidity levels, between 20 and 80 _2 S _3 to MoS _2 greatly enhanced the durability of the coatings at all the tested humidity levels, reaching up to a 760 _2 S _3 and MoS _2 .

In the present work, the friction and galling-prevention properties of a lubricating grease with the addition of Bi2S3 particles have been investigated. To achieve this, commercial lithium greases containing Bi2S3, hexagonal boron nitride, and graphite were employed to lubricate steel–aluminum contacts under different tribological configurations, namely reciprocating sliding tests with varying normal loads and sliding speeds and load scanner tests at 25, 200 and 300 °C. The addition of Bi2S3 enhanced the tribological response of the grease in reciprocating tests and provided protection against galling up to temperatures of 200 °C. However, its performance severely deteriorated at 300 °C. Thus, Bi2S3 showed promising properties as an additive for lubricating greases operating under a wide range of normal loads, sliding speeds, and moderate temperatures.

In the automotive industry, galling is a huge problem either for the tool life or the quality of the stamping metal component. Galling is a severe form of scuffing associated with gross damage to the surface or failure. This work aims to carry out a series of experiments of galling tests at different loads and similar roughness with 6061 aluminum and D2 steel, common materials used in automotive components and tools respectively. A tribometer was employed to generate Galling wear, the button-on-button configuration, according to the ASTM G-196-08 standard. The results show the threshold of minimum load without galling wear. Post-test-surface analysis of the specimens was conducted by confocal microscopy to identify the damage generated during the wear tests. Additionally, a couple of friction tests were carried only to illustrate the friction coefficient behavior under galling conditions.

The erosion-wear behaviour of spark plasma-sintered austenitic stainless steels matrix composite was investigated under high temperature conditions. Erosion-wear behaviour of the composites was conducted at a constant velocity of 18 m/s and impinging angle of 90° at different temperatures of 25, 400 and 600 °C. Hard abrasive alumina particles with particle size of 40 µm were used as erodent. After SPS, relative density of spark plasma-sintered samples decreased with increasing TiN content. Furthermore, the results show a reduction in material loss with increased hardness. However, there was a significant increase in material wastage as temperature increases. Microstructures of the eroded samples indicate that the erosion damage occurs mainly by plastic deformation and brittle fracture. Large fragments in the form of wear debris, pitting, ploughing with slip on the side, misplaced material and a few grooves are observed as well on the SEM images.

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The extensive application of titanium alloys is delimited as their erosion wear properties deteriorate when exposed to erosive and harsh environments. The present research investigates the effects of TiN additions (2, 4, and 6 vol.%) on the Ti-6Al-4V alloy prepared by spark plasma sintering technique. Erosion wear behaviour of the composites was investigated by high-velocity solid particle erosion test and tribometer pin-on-disc friction module method. The duration of the test was 10 min, while the mass loss of the sample was recorded after 2-min interval. The surface analysis and phase identifications of the sintered composites were examined by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Microstructural analysis revealed a transformation from lamellar with β grain boundaries in Ti-6Al-4V alloy to bimodal structures upon addition of TiN nanoparticles. XRD patterns of the alloy indicated an increase in diffraction peaks from lower intensity to high intensity with an increase in TiN nanoparticle content. Erosion is visible in Ti-6Al-4V alloy, 4 and 6 vol.% TiN, but less severe with 2 vol.% TiN addition for all the test times. However, this is due to grain detachment of the hard phase regions between the matrix and the reinforcing phase of the composites. The results showed the presence of micro-voids on the eroded surfaces. It was found that Ti-6Al-4V alloy with TiN nanoparticle addition was resistant to erosion wear, while the recorded steady-state friction coefficients for all the samples range from 0.2 to 0.4. However, an increase in microhardness values ranges from 342 to 513 HV 0.1 .

The spark plasma sintering (SPS) is a type of electric discharge sintering technique used to consolidate metallic/ceramic powders. In this study, spark plasma sintering was used to fabricate 304 stainless steel with TiN addition. The best parameters that influence the sintering process such as sintering temperature, heating time and pressure were investigated. Results show that by varying the amount of TiN, the sintered properties of the composites could be significantly affected. The relative density decreased with the increment of TiN. Microhardness values vary from 270 to 350 HV0.1.

AISI 440C is a high carbon martensitic stainless steel, primarily used in bearing applications. For this study, one group of AISI 440C steel disks was quenched in oil and tempered. Another group was soaked in liquid nitrogen (− 196 °C) immediately after quenching for 5 h and then tempered. The resulting microstructures were analyzed as well as the rolling contact fatigue (RCF) performance using two methodologies, with and without artificial defects. It was found that the microstructural modifications generated by the cryogenic treatments did not improve significantly the RCF resistance of the material. However, this work supports the use of artificial defects as a valid methodology for conducting accelerated rolling contact fatigue experiments.

The trajectory of a ball impacting with an angle on a rigid boundary is recorded with a high-speed camera and the dynamics is reconstructed in a computer. Several experiments are carried out in order to obtain statistical distributions of the trajectory. On the other hand, a continuum model of a viscoelastic material ball simulates the experiment. If the values of the constitutive parameters (e.g. elastic and viscous modulus, friction coefficient, etc.) in the numerical model are correct, the simulated dynamics and the experimental data should match. In this study, the Bayesian inference is applied to identify two constitutive parameters (the friction and viscous coefficients) through statistical measures. The methodology shows to provide a useful tool to solve an inverse problem with a stochastic approach which allows to reference the results in a statistic frame starting from indirect and sparse information.

The purpose of this study is to determinate the influence of surface roughness on the tribological behavior of a lubricated steel against steel tribosystem. Tests were carried out at high pressure and slow sliding speed, in order to simulate at small scale, the contact conditions found in the seal of the threaded joints used in oil & gas casing and tubing strings. Tests were carried out with a simplified block-onring test, varying the surface roughness of rings between 1.3 to 3 m Ra values. A thread compound lubricant containing lead, copper, zinc and graphite was used. During each cycle of test, the normal load was varied linearly between 250 N and 7000 N. An exponential correlation between Ra and Rt roughness values with the wear damage was found and the wear damage of the blocks decreases about 40 percent with the increasing of initial Ra roughness parameter in the movil surface.

Tungsten carbide (WC) is extensively used in industrial processing as cutting tools, wear resistant components and drilling tools owing to the good combination of phenomenal properties. The binder phase of WC is usually cobalt (Co) as a result of good wetting behaviour and excellent solubility with regards to WC particles. However, degradation of WC-Co components when subjected to harsh environmental conditions often results in premature failures during application. In this study, the effect of CrC-Ni on the microstructure, mechanical and tribological properties of WC based cermet produced by spark plasma sintering was investigated. Sintered samples were then analysed and characterized by SEM and EDS. Macro hardness of the sintered compacts were evaluated using Rockwell hardness machine at 150kg load. Subsequently, comparative studies on the tribological behaviour of the experimental samples were performed using a reciprocating wear set up at 200°C. The area of the wear track cross-section was measured using optical profiler and the wear rate in terms of volume loss was calculated. Results showed improved mechanical and tribological properties on WC-20CrC-7Ni sample as compared to WC-Co cemented carbide sample.

Fil: Muller, Camila. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Planta Piloto de Ingenieria Quimica. Universidad Nacional del Sur. Planta Piloto de Ingenieria Quimica; Argentina

In this study, the wear and friction behavior of manganese phosphate coatings with different crystal sizes were investigated. Crystal size was controlled modifying the chemical composition of the phosphating bath, particularly the concentration of the activator which modifies the number of nuclei for crystal growth. Activator concentration range used for this work varied from 0 to 0.7 g/L, and crystal size was measured using image analysis software on scanning electron microscopy photographs. Available volume for lubricant retention was determined measuring the phosphated surface with a 3D optical profilometer. At the same time, lubricated wear tests were carried out using a ring-on-block configuration at low speeds (23 mm/s) and high loads (14,500 N). Wear behavior was determined as the sliding distance to failure, which was noticed through signs of removal of the phosphate along with the increase of coefficient of friction. It was found that there is a competition between the availability of volume to hold the lubricant, which increases with the crystal size, and the surface coverage, which diminishes as the crystal size grows. Optimal results were obtained for an activator concentration of 0.3 g/L, which meant an average crystal size of 16 µm.