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 assesses MP in water, sediment, gills, and digestive tract of the oyster Magallana gigas in three Bahía Blanca estuary sites, Argentina, using, Pollution Load Index (PLI) and SEM/EDX (Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy) and FTIR (Fourier-transform infrared spectroscopy) techniques. A total of 51 MPs were detected in water (mean: 16 items L-1) and 126 in sediments (mean: 1399 items Kg-1) with no significant differences between sites. In oysters, 186 MPs were found, with no significant differences in the MPs load between gills (mean: 2.41 items g-1 w.w), digestive tract (2.06 ± 2 items g-1 w.w), and the total tissues. Transparent fiber MPs were predominant, with cellulose, polyamides, polyethylene terephthalate and polyethylene being common polymers. SEM/EDX showed Si, Fe, Cl, Na, Ti, Al, K, Ca and suspended particulate matter on MP surfaces. The PLI indicated a low-risk level for estuary bivalves and water, suggesting minimal MPs impact.

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.

Super duplex stainless steels (SDSS), widely used in industries such as offshore oil and gas, offer a unique combination of high strength and corrosion resistance. However, surface hardening treatments are crucial to enhance their performance and extend service life. This work investigates the effect of plasma nitriding on the tribological behaviour of SDSS SAF 2507. Samples are treated without prior polishing (as received, AR) at ultralow temperatures (250 and 300 degrees C) aiming to avoid detrimental CrN precipitation. Comprehensive microstructural characterization, corrosion studies, and tribological tests (scratch and ball-on-disc) are conducted on samples that do not present CrN (PN). Results indicate that the hardness of PN samples nearly doubles that of AR samples due to the presence of expanded austenite. Corrosion tests show improvements in passivity for PN samples. In scratch tests, while the AR material undergoes progressive plastic deformation, in PN material the nitrided layer breaks down only after reaching a critical load. In ball-on-disc test, wear rates are remarkably lower for PN condition compared to AR condition. Wear mechanism is tribo-oxidative and abrasive for the AR condition. Wear of PN samples is characterized by asperity break-off and ratcheting. The nitrided layer in PN samples exhibits an enhanced load-bearing capacity that improves wear resistance in both tests.

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.

It is widely recognized that the measures adopted during the pandemic resulted in a significant number of face masks entering marine environments. One key aspect is to investigate the behavior of such contaminants in coastal environments. In the present study, in situ experiments were carried out to investigate the physicochemical changes of two types of face masks, as well as their interaction with intertidal biota. Chemical analyses showed no notorious signs of photo-oxidation while confirming that face masks are entirely composed of synthetic polymers. However, scanning electron microscopy showed an affectation of the physical structure on the outer layer of KN95 respirators, as well as the presence of environmental elements accumulating. Interaction with intertidal biota suggested that face masks serve as a suitable substrate and hiding spot for bivalves and polychaetes. Investigating the alteration of such contaminants in the intertidal shore provides new insights into their behavior after entering the ocean.

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 .

This study, surveyed the presence of PPE on the streets of three metropolitan cities of South America to investigate the potential of metal-nanoparticles (Me-NPs) and microplastics (MPs) leaching from face masks. In order to do so, the toxicity characteristic leaching procedure (TCLP) and seawater solution under controlled conditions were utilized. Results showed there was a relationship between low-economic income areas of South American metropolitan cities and the quantities of PPE waste on the streets. The chemical characterization revealed multiple polymer types in PPE waste, while additives like CaCO3 and MgO, and nanoparticles such as Cu, Zn and Ag-NPs were identified in face masks. Based on the exposure of textile face masks impregnated with nanoparticles and surgical face masks to simulate solutions, a higher/larger number/quantity of MPs fibers was released from textile face masks than from surgical ones. In TCLP test results, Cu-NPs concentrations exhibited a range from 35,900 to 60,200 μg.L-1, and Zn-NPs from 2340 to 2380 μg.L-1 in textile face masks, whereas Ag-NPs concentrations ranged from 65 to 914 μg.L-1 in textile and surgical face masks. Thus, the amount of Me-NPs released depends on: the size of the nanoparticles, concentration, fabric type, and the impregnation method of the textiles.

Here, we build and characterize a single-stage gas-gun microparticle accelerator, where a pressurized gas expands and launches particles on a target. The microparticles in the range of 60-250 μm are accelerated by the expansion of pressurized nitrogen. By using a high-speed camera, we study how the velocity distribution of accelerated particles is modified by particle size, pressure in the gas reservoir, valve's opening time, and diaphragm's thickness and composition. We employ this microparticle accelerator to study the impact of glass particles with diameters of (69 ± 6) μm accelerated at moderate velocities ∼ (10-25) m/s, using films of poly-dimethylsiloxane as targets.

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.

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 .

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.

Nanotechnologies offer tremendous potential when it comes to modifying the microstructure of steel through the incorporation of nanoparticles. While typical production methods for metal-matrix composites are difficult and expensive, conventional casting routes suffer from inhomogeneity and agglomeration of the added nanoparticles. The aim of this study was to investigate the feasibility and possibilities of introducing nanosized particles into a steel matrix through a conventional casting process and to determine the effect of different nanoparticles and methods of incorporation on the strength, toughness, and high-temperature wear resistance of martensitic steel. The results show that also in the case of a conventional casting process, it is possible to obtain a homogeneous distribution of nanoparticles in the metal matrix, resulting in improved strength, maintained toughness, and up to five times better high-temperature wear resistance of the Mn-Cr steel. However, the rate of improvement greatly depends on the method and type of nanoparticles incorporation. The most promising results were observed for the combination of carbon nanotubes, oxide nanoparticles, and dispersant, sealed in a steel tube, with the dispersant providing the uniform distribution, the carbon nanotubes delivering the good toughness and the adhesive wear properties, and the oxide nanoparticles ensuring oxidation and abrasive wear resistance.

Cryogenic treatments have been employed over the past three decades for both tool and high-alloy steels to improve their wear resistance, mainly through the transformation of retained austenite and the precipitation of fine carbides. However, as the enhancement of one material property is often at the expense of another, it is interesting to evaluate the effect of this type of treatments on the fracture toughness. The objective of the present work was to determine the plane-strain fracture toughness of a cryogenically treated low-carbon AISI 420 martensitic stainless steel by means of standardized fracture tests, performed in accordance with the ASTM E399 and ASTM E1820 standards. In this study, it was experimentally demonstrated that cryogenically treated specimens showed a simultaneous increase in the Km and hardness of 30 % and 5 %, respectively, compared to conventionally treated specimens.

The objective of the present work is to characterize the wear behavior of a cryogenically treated low-carbon AISI 420 martensitic stainless steel, by means of ball-on-disk tribological tests. Wear tests were performed under a range of applied normal loads and in two different environments, namely a petrolatum bath and an argon atmosphere. Wear tracks were analyzed by both optical and scanning electron microscopy and Raman spectroscopy to evaluate wear volume, track geometry, surface features and the tribolayers generated after testing. This paper is an extension of the work originally reported in the VIII Iberian Conference of Tribology (Prieto and Tuckart, in: Ballest Jiménez, Rodríguez Espinosa, Serrano Saurín, Pardilla Arias, Olivares Bermúdez (eds) VIII Iberian conference of tribology, Cartagena, 2015). In this study, it has been experimentally demonstrated that cryogenically treated specimens showed a wear resistance improvement ranging from 35 to 90% compared to conventionally treated ones.

Cryogenic treatments are increasingly used to improve the wear resistance of various steel alloys by means of transformation of retained austenite, deformation of virgin martensite and carbide refinement. In this work the nanotribological behavior and mechanical properties at the nano-scale of cryogenically and conventionally treated AISI 420 martensitic stainless steel were evaluated. Conventionally treated specimens were subjected to quenching and annealing, while the deep cryogenically treated samples were quenched, soaked in liquid nitrogen for 2 h and annealed. The elastic–plastic parameters of the materials were assessed by nanoindentation tests under displacement control, while the friction behavior and wear rate were evaluated by a nanoscratch testing methodology that it is used for the first time in steels. It was found that cryogenic treatments increased both hardness and elastic limit of a low-carbon martensitic stainless steel, while its tribological performance was enhanced marginally.

Purpose– The purpose of this study is to select a proper surface treatment to enhance wear resistance of engine camshafts. The camshaft is a relevant part of a diesel engine which works under torsion, fatigue and wear efforts. They are usually manufactured by casting, forging or machining from forged bar of low alloy steels, and in most cases, the machined surfaces are quenched and tempered by induction heating. After that, in many cases, to withstand the efforts imposed on the active surfaces and improve tribology and fatigue properties, the industry used for decades, thermochemical technologies such as salt bath or gaseous nitriding and nitrocarburizing processes.Design/methodology/approach– This paper studied the effects of plasma nitriding and plasma nitrocarburizing, on the tribological behaviour of the steel SAE 1045HM3 proposed to produce camshafts. After the plasma treatments, the change in surface roughness was measured; the modified layers were studied by X-ray techniques and its thickness by optical microscopy. The diffusion zone was evaluated by Vickers microhardness determinations. Tribology tests were performed by pin-on-disc configuration using WC ball as a counterpart.Findings– Results show that plasma nitrided samples present the best tribological behaviour compared with the nitrocarburized ones; also, the influence of the roughness produced by the thermochemical processes appears to be important.Practical implications– Although both the plasma treatments have been applied for many years, and also reported separately in the scientific literature, there was no information comparing these two treatments for carbon steels, and also, there is not much about tribology in lubricated conditions of nitrided and nitrocarburized carbon steels. In fact, it is not proved that the porosity of the nitrocarburized layer is beneficial for wear resistance in lubricated conditions. In this paper, it was proved that at least in the tested conditions, it is not.Originality/value– Gas or plasma nitrocarburizing is usually recommended for this kind of applications, although the modified layer is porous. This paper attempts to prove that nitriding could be better than nitrocarburizing, even with a thinner white layer.