This work investigates the structure, mechanical, and tribological properties of Ta-xN coatings deposited using reactive High Target Utilization Sputtering (HiTUS) with a focus on the role of ...tribological layers formed in the sliding contacts. The scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy observations revealed that the gradual increase of nitrogen flow results in the transition from textured fcc Ta structure (without nitrogen) toward mixed sub-stoichiometric Ta-Ny/Ta2N/amorphous structures up to near-stoichiometric fcc TaN coatings. The highest hardness HIT ∼37 GPa and indentation modulus EIT ∼375 GPa as well as the lowest coefficients of friction (COF) in the range 0.16–0.36 and wear rates around 3 × 10−7 mm2/N·m were obtained in the layer with Ta2N structure. The unique combination of low COF and high wear resistance combined with high hardness and stiffness were attributed to the shear sliding between Ta2O5-based transfer film in the wear track and pure alumina ball.
The tribocorrosion behavior of type 316L stainless steel and CrN coated 316L by PVD was investigated in seawater environment. Tests were carried out in a triboelectrochemical cell using a ...ball-on-plate tribometer integrated with a potentiostat for electrochemical control. Sliding contact against silicon nitride balls had a significant effect on the open circuit potential (OCP) and corrosion potential (Ecorr) for 316L. However, the OCP for the CrN coating remained relatively stable during the sliding. Tribocorrosion tests performed under various applied potentials demonstrated that the friction coefficient decreased and wear-loss increased as the applied potential increased from −1V to 0V. Under cathodic potential of −1V, abrasive wear form of mechanical wear dominated the wear of 316L stainless steel. As the potential increases, the general corrosion was observed and tribo-corrosive contributions to the wear increased. Plastic deformation dominated the wear process of CrN coating under a cathodic potential. With an increase in potential, the mechanical wear contribution decreased and corrosion-accelerated wear contribution increased. At high anodic potential (0.5V), pitting corrosion occurred in the wear track and on the outer part of wear track on 316L and CrN coated 316L.
•Sliding contact had a significant effect on the OCP and Ecorr for 316L.•The OCP for the CrN coating remained relatively stable during the sliding.•The friction coefficient decreases and wear volume increases as potential increased.•The corrosion-accelerated wear contribution increases with increase of potential.
The paper presents a view on the achievements, challenges and prospects of mechanochemistry. The extensive reference list can serve as a good entry point to a plethora of mechanochemical literature.
In this study, AISI52100 steel surfaces were coated with bilayer Cr–N/TiB2 thin films in total thickness of 65 and 120 nm by magnetron sputtering. The CrN/TiB2 thin-films deposited under 10 and 20 ...sccm N2 flow whereas no N2 flow was used for a Cr/TiB2 thin film. The friction and wear behaviors of these bilayer thin-films consisting of metallic (Cr)/ceramic (TiB2) and ceramic(CrN)/ceramic(TiB2) layers were investigated via the tribometer tests under unlubricated and lubricated conditions. Bilayer thin-films were characterized by nanoindentation, microscopic and spectroscopic analysis. Results showed that N2 flow has significant effects on mechanical characteristics of bilayer coatings. Furthermore, the Cr/TiB2 thin film with a high porosity showed good tribological performance under 2 GPa contact pressure whereas the CrN/TiB2 thin film deposited at high N2 flow with high thickness and hardness showed the best tribological behavior.
•Magnetron sputtered bilayer Cr–N/TiB2 thin-films deposited on the AISI52100 steel surface.•The nitriding process had a significant effect on CrN layer thickness and TiB2 microstructure.•The pores filled with lubricant enhanced the lifetime of the bilayer Cr–N/TiB2 coatings.•The metal/ceramic layer with a functional ceramic layer showed different antiwear behaviors.
Frictional heating of metals at reciprocating or sliding contacts in high-pressure oxygen environments poses a risk of catastrophic metal fires. This phenomenon, known as frictional ignition, has ...been implicated in several high-profile failures of oxidizer-rich turbopumps, presenting an ongoing challenge in the development of next-generation reusable rocket engines. Early NASA investigations on frictional ignition of candidate turbine materials identified oxide dispersion-strengthened Ni-base superalloys as exceptionally resistant to ignition. In this study, we performed high-speed sliding, frictional ignition experiments on binary Ni-Cr alloys and two oxide dispersion-strengthened Ni-Cr alloys – MA754 and MA758. Analysis of recovered non-ignited samples revealed the in situ growth of oxide tribolayers on rubbing surfaces during sliding. An order of magnitude reduction in friction coefficient during the initial stages of sliding was attributed to the formation of these tribolayers. An abrupt increase in friction coefficient preceding ignition was linked to tribolayer breakdown, exposing the hot underlying metal to high-pressure oxygen. The oxide dispersion-strengthened alloy MA754 was the only material that did not ignite under any test conditions. Its specific content of Cr and Y2O3 dispersoids synergistically promote rapid growth of a thick, adherent oxide tribolayer strengthened by refractory Ni2CrO4 precipitates. These features collectively mitigate tribolayer breakdown, suppressing ignition. The present results highlight the importance of tribolayer stability in achieving frictional ignition resistance and suggest alloy design strategies for tailoring oxidational wear behaviors to develop intrinsically ignition-resistant materials.
•Frictional ignition behaviors of binary Ni-Cr alloys and two oxide dispersion-strengthened Ni-Cr alloys (MA754, MA758) were assessed through high-speed sliding experiments in high-pressure oxygen.•All materials exhibited a decay in friction coefficient with time due to the in situ growth of a lubricating oxide tribolayer.•Ni-20Cr was the most ignition-resistant of the binary Ni-Cr alloys, with the lowest friction coefficient, highest ignition temperature, and longest ignition time.•MA754 is the only material that did not ignite in any test, highlighting a synergistic interplay between 20 wt% Cr content and Y2O3 dispersoids in MA754.•Comparing the MA754 and Ni-20Cr tribolayers indicates that addition of Y2O3 accelerates growth of the protective tribolayer, enhances the toughness of the metal/tribolayer interface, and mitigates plastic deformation of the underlying metal.
•Recent achievements in three types of friction modifiers are reviewed.•Lubrication mechanisms of friction modifiers are summarized.•Suggestions for the future directions of friction modifiers are ...proposed.
Due to the increasing demand of low emission and fuel economy, friction modifiers have been widely used in lubricating compositions to adjust friction and wear properties of lubricants. Recent achievements in the application of friction modifiers for liquid lubricants (2007–present) are reviewed in this paper. There are three types of friction modifiers for liquid lubricants: organomolybdenum compounds, organic friction modifiers, as well as nanoparticles. The tribological properties and lubrication mechanisms of these friction modifiers are discussed. The problems and some suggestions for the future directions of research on friction modifiers are proposed.
Ashless dialkyldithiophosphate (DDP) antiwear additives are good candidates to replace the widely used metallic DDPs such as zinc dialkyldithiophosphate (ZDDP), which are less environmentally ...friendly. A newly designed in-situ tribological rig was utilised to perform in-situ synchrotron X-ray absorption spectroscopy (XAS) in order to examine the decomposition reactions of two types of DDPs; acidic and neutral. The tribological experiments showed that the two DDP additives decomposed to form protective tribofilms on the steel surface, which provided better antiwear protection than ZDDP regardless of the tribofilm thickness. The neutral DDP formed a thinner tribofilm (about 33 nm) than ZDDP (about 41 nm), whereas the tribofilm of the acidic DDP had a much lower thickness (<7 nm) but more superior antiwear protection. The two DDPs also provided lower friction coefficient (<0.1) than the 0.12 provided by ZDDP. The XAS experiments suggest that the DDPs decompose to form initially iron sulphate, which is quickly reduced to sulphide before forming the phosphate layers of the protective tribofilm. These layers consisted initially of iron phosphate of short chains but as rubbing continued organic phosphate with long chains started to form.
•Acidic DDP forms thinner ( <7 nm) but more protective antiwear tribofilm.•Acidic and basic DDPs exhibit lower friction coefficient than ZDDP.•DDPs decompose to form initially iron sulphate and short iron phosphate.•DDP tribofilms’ top layers consist of long chains of organic phosphate.
This study successfully synthesizes CoAl-hexametaphosphate layered double hydroxide (HMP-LDH) via anion exchange. The application of HMP-LDH leads to substantial wear and friction reduction of 88% ...and 25%, respectively, outperforming the PAO-4 base oil. In-depth characterizations of tribofilms formed on wear scars and tracks were conducted using various techniques, including Raman, X-ray photoelectron spectroscopy, scanning transmission electron microscopy - energy dispersive X-ray spectroscopy, and cryo-electron energy loss spectroscopy. It was found that the predominant composition of the tribofilm consists of mixed oxide and phosphate species. Notably, metallic cobalt is observed near the tribofilm-steel interface. Nanoindentation and nanoscratch were performed on the HMP tribofilm. The relationship between the nanostructure and nanomechanical properties and their influence on friction and wear have been revealed.
•1 wt% HMP-LDH in PAO-oil improved wear and friction by 88% and 25%, respectively.•HMP-LDH tribofilm consists of mixed oxide and phosphate species.•Metallic cobalt was found at the tribofilm-steel interfaces under atmospheric conditions.•Cobalt diffusion enhances the tribofilm bonding strength.•Nanomechanical properties are evaluated by nanoindentation and nanoscratch with a NorthStar tip.
Ti-40Al-10 V alloys with nearly lamellar structure (HIPed) and refined (B2 +γ) microstructure (HT) were used to investigate the correlation between tribological behavior and microstructural ...characteristics at elevated temperatures. Results showed that owing to high ratios of TiO2/Al2O3, the HIPed samples presented low friction coefficients at high temperatures. As for the wear rates at 400 °C, due to the differences in grain size and γ phase content, a delamination of discontinuous oxide film occurred in the HIPed sample, while oxide film closely adhered to the HT sample, leading to an improved wear resistance in the HT samples. At 800 °C, the wear rate of HT alloys was higher than that of HIPed samples because of obvious plastic deformation in HT samples.
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