Wear Scars Research Articles

Micro/Nanosilver Contribution in Modifying the Lubrication Film to Improve Friction and Wear Behaviors of TiAl-10 wt.%Ag Composite

Tribological performances of solid films are studied to improve their application range while retaining the longevity and high accuracy of TiAl alloy. For a ball-on-flat tribopair system, addition of micro/nanosilver improved the tribological behaviors of TiAl-10 wt.% Ag self-lubricating composite (TASC), compared to those of TiAl alloy. Notably, during microstructure evolution of the wear scar cross-section, a large amount of silver migrated from the TASC to the wear scar, and the silver distributions increased. This influx continuously enriched silver on the wear scar cross-section and formed a low-hardness lubrication film. Concurrently, a large amount of wear debris from the dry sliding wear contributed enough refinements to form a high hardness grain refinement layer. The results confirmed the formation of a 0.75 GPa hardness film with solid lubrication on a grain refined layer of 6.86 GPa hardness, resulting in excellent antifriction and wear resistance from 72 min to 90 min of the TASC. These results can help to evaluate the tribological characteristics for their commercial application and can conceptualize possible solutions for TiAl alloy-base components.

Graphite infused ionic liquid greases

Electrically conductive lubricating greases are vital in improving the efficiency of electric motors as they can reduce friction and wear as well as avoiding electrical arcing at the same time. In this study, electrically conductive greases were produced using two ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium acetate ([EMIm] [Ac]) and 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([EMIm][TFMS]) in combination with solid lubricants, i.e. polytetrafluoroethylene and graphite. The electrical and thermal conductivities as well as lubricities of these two IL based greases were measured and compared to conventional mineral oil based greases of the same compositions. Results show that the electrical conductivities of IL based greases produced in this study are comparable to commercially available conductive greases, which are two orders of magnitude higher than mineral oil based greases of the same compositions. The friction and wear resistances of IL based greases are also improved compared to mineral oil based greases. Among the three base liquids for greases, [EMIm][TFMS] performs best; it produces greases that have lower friction coefficients, smaller wear scars as well as higher electrical and thermal conductivities.

Reinforced mechanical properties of plasma-sprayed Fe-based amorphous composite coatings by in-situ TiNx/TiOy

Ceramic particle-reinforced Fe-based amorphous coatings have received extensive attention due to their excellent strength and wear resistance. In this paper, TiNx/TiOy -enhanced Fe-based amorphous coatings were prepared by reactive plasma spraying technology, and the effect of eggshell-like TiNx/TiOy on the comprehensive mechanical properties of Fe-based amorphous coatings was systematically studied. The results showed that the hardness of the composite coating was significantly higher than that of the amorphous single-phase coating. Moreover, indentation experiments showed that TiNx/TiOy effectively confined crack growth in the amorphous phase. Though the bonding strength of the composite coating was lower than that of the pure amorphous coating, but still maintained a high bonding force of 20.68 MPa. Through the wear experiment, it was found that the wear scar of the composite coatings appeared plastic deformation, the friction coefficient and wear mass loss were both greatly reduced, and the optimal wear performance appeared in the composite coating with 15% Ti addition. In addition, SEM, EDS analysis, and the first-principles simulation results demonstrated the good bonding between Ti-containing compounds and Fe-based alloys.

Modified Graphene/Muscovite Nanocomposite as a Lubricant Additive: Tribological Performance and Mechanism

Modified graphene/muscovite (MGMu) nanocomposite was synthesized with muscovite (Mu) and silane coupling agent modified graphene oxide through a simple hydrothermal method that exhibited excellent dispersion stability in oil. Compared with the base oil sample, the average friction coefficient and wear scar diameter of the MGMu oil sample decreased by 64.4 and 20.0%, respectively, and the microhardness of its wear scar was increased by 16.1%. The MGMu showed better tribological performance than its individual component due to the synergetic effect between the two components. The lubrication mechanism was proposed according to the morphology, chemical composition, and microhardness of the surface of wear scars. MGMu as an oil additive could fill between the friction pairs, cling to some asperities, and occur relative sliding between unit layers, thus playing a role in lubrication. It was found that MGMu would react with the surface of the friction pair during the friction process to generate Fe2O3, SiO2, SiC, and new aluminosilicate, which formed a self-repairing layer with high hardness. This chemically reactive film exhibited a lower shear strength, which made the oil sample containing MGMu have a lower coefficient of friction.

An experimental investigation of galling phenomenon generated in an alternated sliding ring-on-ring interface: Application to a full-scale solid lubricant interface

A fully instrumented ring-on-ring galling test has been developed based on the ASTM G196 test principle. Torque records allow computation of the coefficient of friction and other tribological parameters to capture wear behavior of the interface. Contact electrical resistance is also recorded helping to detect galling onset in the contact. A solid lubricant anti-galling solution in OCTG connections involving a coated versus steel interface has been studied. Tests have been stopped at different sliding distances to perform surface analysis and characterize wear mode and severity. Wear scars have been expertized using optical, SEM, EDS, surface and μ-hardness profile analysis such that the degradation scenario of the coating and the steel surface can be drawn up. Moreover, an analysis in terms of friction coefficient can be developed describing the evolution from pure lubricated interface to fully galled interface.

In-situ intercalated pyrolytic graphene/serpentine hybrid as an efficient lubricant additive in paraffin oil

In this study, a novel lubricant additive hybridizing pyrolytic graphene and serpentine was reported for the first time to enhance the tribological performance of paraffin oil. The in situ produced pyrolytic graphene from pyrolysis of citric acid was observed to be intercalated into the interlayer of serpentine sheets. The structure, morphology and chemical composition of the composite lubricant additives were characterized by scanning electron microscope, X-ray diffractometer and Fourier transform infrared spectroscopy. In addition, the anti-wear and friction-reduction mechanisms of the hybrid lubricant additive, owing to its activity on the friction interface, were disclosed by exploring the morphology and component of the wear scar after friction. The tribological results revealed that introducing a small amount of pyrolytic graphene/serpentine lubricant additive (0.2 wt%) to the base oil could effectively reduce the friction coefficient (~87%) and wear loss (~71%) in comparison with neat paraffin oil. First-principles calculations based on density functional theory were further performed to uncover the lubrication mechanism of the hybrid. Therefore, the pyrolytic graphene/serpentine hybrid reported herein represents a new strategy to prepare high efficient lubricant additive.

Microstructure and tribological behavior of plasma spray Ni60 alloy coating deposited on ZL109 aluminum alloy substrate

This paper investigated the microstructure and tribological behavior of Ni60 alloy coating prepared on the surface of aluminum alloy (ZL109) by plasma spray. The ANSYS software was applied to compare the deformation and temperature of nickel-based alloy coating deposited on aluminum alloy piston with the thickness of 300 µm, 400 µm and 500 µm. X-ry diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the phase, microstructure and chemical composition of Ni60 alloy coating. Besides, fractal theory was used to study the geometric morphology of materials. The tribological properties of the coating were investigated under oil-lubrication at 100 °C through the circular cyclic test with Si3N4. The result shows that the piston skirt deformation was the smallest when the coating thickness was 300 µm. Multiple phases such as chromium carbide and Ni3Fe phases were contained in the coating, and Si element was dispersed in the Ni60 alloy powders with the form of silicon oxide, which enhanced the hardness and oxidation resistance of the coating. The porosity of the coatings prepared under three power conditions (P = 40 kW, P = 50 kW and P = 45 kW) were 1.58%, 1.47% and 0.97%, respectively. When the load increased from 80 N to 100 N, the depth and width of the wear scar increased and the wear volume added from 1.54 × 108 μm3 to 3.45 × 108 μm3. The friction coefficient of the coating increased with the increment of load. By comparison, the coating with moderate spraying power has less weight loss and better wear resistance under higher wear load.

The Effect of 1T Phase Molybdenum Disulfide on the Tribological Performance of Polyethylene Glycol

In our research described in this paper 1T Phase Molybdenum Disulfide/Polyethylene Glycol (200) (1T-MoS2/PEG) was studied as a lubricant for steel-steel contact with the goal of minimizing or eliminating galling. The morphology and structures of 1T-MoS2 were analyzed by various techniques, such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the friction performance of oleic acid (OA) modified 1T-MoS2 as a lubricants additive for PEG was investigated. The results of the friction test indicated that the average friction coefficient and wear scar diameter of PEG containing 0.1875 wt% 1T-MoS2 were 14.30% and 46.90% less than those of pure PEG, respectively. However, those of 0.1875 wt% 1T-MoS2/PEG modified by OA as lubrication additives were 47.83% and 56.79% lower than those of pure PEG. 1T-MoS2 nanoparticles can not only fill the inherent grooves on the surface of the steel ball, but also form a friction lowering film on the friction interface, thus reducing friction and wear, which was seen from the results of scanning electron microscopy (SEM) and element mapping of the wear scar. This study, most importantly, provides a foundation for the use of 1T-MoS2/PEG and OA/1T-MoS2/PEG as effective lubricants to reduce the friction problems in the mechanical industry.

Reliability of Friction and Wear Characteristics of Surface-Strengthened Iron-Based Powder Metallurgy Materials

With the continuous improvement of metallurgical technology, iron-based powder surface strengthening has become one of the methods of making powder metallurgy. The iron-based powder can improve the friction and wear characteristics of metallurgical materials. This article mainly studies the methods that can strengthen the friction and wear characteristics of iron-based powders. Finally, the amorphous alloy method is used, and then the surface sulfide is used to reduce the friction coefficient and increase the surface hardness of the alloy. Through experiments on the control variables of the sulfurizing formula, the optimal sulfurizing formula is finally obtained. Then through the change of time and temperature, it is concluded that the friction coefficient can be reduced to 0.022 when the time is 3 h, and the wear scar depth is reduced to 0.019 mm. The effect is best when the temperature is 40 °C, and the friction coefficient can be reduced to about 0.02, the depth of the wear scar is also maintained at 0.019 mm.

Enhanced service life of nickel-based alloy die for copper extrusion by pulsed magnetic field

As an efficient and eco-friendly strengthening technology, pulsed magnetic field treatment (PMT) was used to prolong the service life of nickel-based die in the process of copper extrusion. The service life, mechanical properties, failure characteristics and microstructure evolution of the die were investigated. The results show that after PMT, the average service life of the die is increased by about 34.9 %, and the tensile strength and elongation of the alloy are increased by about 7.3 % and 34.6 %, respectively. Enhanced performance comes from the fact that PMT promotes the aggregation of disordered solid solution elements in the γ matrix, and the number of fine γ’ precipitates in the alloy is significantly increased. At the same time, the dislocation density and the degree of entanglement increase. In addition, the tribological behavior of the die treated with PMT from severe adhesive wear and abrasive wear on the die surface to mild abrasive wear on the adhesive layer, with reduced surface roughness and wear scars.

Carbon fiber reinforced degradable poly(hexahydrotriazine) composites with excellent self-healing and improved wear resistance

Inspired by the living tissues self-healing strategy, polyethylene wax (PEW) as a healing agent was embedded into poly(hexahydrotriazine)s (PHT) cross-linked networks by a simple in-suit polymerization reaction to obtain a self-healing carbon fiber reinforced polymer composite (CFRPs). The resultant CFRPs exhibited outstanding wear resistance with a minimum friction coefficient of 0.10 and acquired a high tensile strength of 287 MPa. In addition, the wear scar could readily heal after heating at over 100 °C for 60 s, and the friction coefficient stabilized around 0.12 after three-cycle tribological tests, which was owing to the formation of the protective layer by the low-melting-point PEW thermal migration to the wear track. This work opens up a new opportunity for fabricating self-healing CFRPs with durability and recyclability.

Investigation on fretting wear mechanism of 316 stainless steel induced by Ni dissolution during pre-immersion corrosion in the liquid lead-bismuth eutectic (LBE)

Heat transfer tubes in nuclear power plants are easily damaged by fretting wear. The fretting behaviour of the heat transfer tube related to the lead-bismuth eutectic (LBE) alloys needs to be investigated. In this work, the effect of pre-immersion corrosion in LBE of AISI 316 stainless steel on fretting behaviour is explored in detail. Following short-duration corrosion (specimens denoted C0 and PC1), no significant change occurred during corrosion, and after the fretting test, the wear scars were shallow, with adhesive wear being the dominant wear mechanism. Following long-duration corrosion (specimens denoted PC2 and PC3), the dissolution of Ni and the formation of an oxide layer were the main corrosion mechanisms. After the fretting tests, the wear scars were deep, demonstrating a degraded anti-wear property, and fretting fatigue wear was dominant. The degradation of the fretting wear resistance in specimens PC2 and PC3 can be attributed to the absence of the protection of NiO in the tribolayer, the large grain size, and the weak plastic deformation accommodation ability. The underlying mechanism is the dissolution of Ni induced by pre-immersion corrosion in the LBE. The present work provides useful information on the fretting behaviour of heat-transfer tubes in nuclear power plants related to the LBE environment.

Tribological Performance and Rheological Properties of Engine Oil with Graphene Nano-Additives

Nanoparticles dispersed in lubricants are being studied for their ability to reduce friction and wear. This paper examines SAE 5W-30 oil enhanced with dispersed graphene nanoplates for tribological and rheological properties. Graphene nanoplate (GNs) concentration effects on the rheological and tribological properties of 5W-30 base oil (0.03, 0.06, 0.09, 0.12, and 0.15 wt percent) were tested. Under various loads, a four-ball testing model was used to conduct a tribological analysis (200, 400, 600, and 800 N). Kinematic viscosity is calculated, and base oil and nanofluid-added 5W30 lubricant are compared for thermal conductivity and flashpoint. Wear scar and coefficient of friction improved by 15% and 33% with nano-additives. When related to the base oil, the flashpoint, thermal conductivity, kinematic viscosity, and pour point all increased, by 25.4%, 77.4%, 29.9%, and 35.4%, respectively. The addition of GNs improved the properties of 5W30 engine oil.

Dependence of the lubrication enhancement of alkyl-functionalized graphene oxide and boric acid nanoparticles on the anti-oxidation property

The influence of anti-oxidation property of nanoparticles on the tribological properties is rarely reported. In this study, the alkyl-functionalized graphene oxide (FGO) and alkyl-functionalized boric acid (FBA) were fabricated as oil additives to explore their lubrication effectiveness. FBA exhibited remarkable lubricating properties which reduced friction coefficient by approximately 24 % and the wear depth by about 94 %. However, the friction coefficient and wear depth of FGO were reduced by only 9.5 % and 44 %, respectively. Worn surface analysis shows a bunch of deep-plowing on rubbing surface in the case of FGO, while the wear scar was smooth and almost wear-free for FBA. Lubrication mechanism analysis by X-ray Photoelectron Spectroscopy revealed the formation of carbon-based tribofilm for FGO and boron-based tribofilm for FBA during rubbing. In the thermal behavior analysis, graphene oxide (GO) nanoparticles were completely decomposed at 650 °C, whereas, B2O3 nanoparticles remained stable. It indicated that the excellent thermal stability and anti-oxidation property of boron-based tribofilm benefited to the lubrication enhancement. This study highlights the importance of oxidation resistance in designing novel nanoparticle additives, and the enhancement of oxidation resistance of GO will be a promising way to further application as oil additives.

Methyltrioctylammonium Octadecanoate as Lubricant Additive to Different Base Oils

This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the miscibility of the FAIL in the base oils. The addition of the FAIL hardly changed the density of the base oils and the viscosity slightly increased at lower temperatures. The tribological performance of the base oils and their blends with the FAIL was determined using three different tests: Stribeck curve determination and tribofilm formation tests, both under sliding/rolling motion, and reciprocating wear tests. The M1 + FAIL blend showed the lowest friction values under the mixed lubrication regime due to its higher viscosity, while the E1 + FAIL showed the lowest friction values under the elastohydrodynamic lubrication regime, which may well have been due to its higher polarity. Only the E1 + FAIL blend outperformed the antiwear behavior of the base oil, probably because it has better chemical affinity (higher polarity) for the metallic surface. SEM images showed that the predominant wear mechanism was adhesive-type with plastic deformation and XPS studies proved that the presence of increasing amounts of organic oxygen on the wear scar caused better antiwear performance when the E1 + FAIL blend was used.

Microstructure evolution and wear mechanism of in situ prepared Ti–TiN cermet layers at high temperature

The preparation of cermet-modified layers on the surface of titanium alloys using lasers is an effective method to improve their wear resistance. In this study, a typical Ti–TiN composite cermet layer was prepared in situ on the surface of a titanium alloy by laser melting under a N2 atmosphere. The microstructure and wear behavior were characterized. The rapid cooling of the laser and the difference in the physical and chemical properties of the ceramics and metals led to the appearance of stacking faults in the TiN ceramic phase, dislocation cells in the Ti phase, and semi-coherent interfaces with stacking fault groups as transition structures. Friction test analysis shows that the formation of the Ti–TiN cermet layer significantly improves the surface wear resistance of the titanium alloy. In particular, the wear resistance is improved by approximately one order of magnitude at 500 °C. The accumulative strengthening and stable strain hardening were formed by the deformation dislocation network in the TiN phase, polycrystalline transformation and dislocation interaction in the Ti phase. These microstructural transformations improve the wear resistance of the cermet layer. The amorphous-crystalline nanocomposite friction glaze layer formed in the wear scar at high temperatures further improves the wear scar strength, and the uniform plastic deformation during friction shear inhibits wear and balances the force distribution on both the phases during the friction process.

Mechanical and tribological behavior of TiB2/ Al2O3 coating on high-speed steel using electron beam deposition

At 600 °C, a TiB2-Al2O3-Ti(20 %) coating was deposited by electron beam deposition (EBD) on high-speed steel (HSS) substrates. X-ray diffraction and field emission scanning electron microscope and energy-dispersive X-ray spectroscopy were used to investigate the structural analysis and surface morphology of TiB2-Al2O3-Ti(20 %) coating. The effect of load on Young’s modulus and hardness was studied using mechanical experiments on TiB2-Al2O3-Ti(20 %) coatings at modest loads ranging from 2000 to 10000 µN. Nanoscratch was done on TiB2-Al2O3-Ti(20 %) coated on HSS and uncoated HSS sample at a low load of 0–10000µN, and the coated sample had a COF of 0.08–0.21, whereas the uncoated sample had a COF of 0.2–0.46. To investigate the deformation and failure behavior of the coating/substrate combination and their nanotribological properties, nano wear experiments were done on TiB2-Al2O3-Ti(20 %) coatings at loads ranging from 0.5 N to 2 N. The results demonstrate that Young’s modulus and hardness of the TiB2-Al2O3-Ti(20 %) coating decreases when the load increases. The TiB2-Al2O3-Ti(20 %) coating has a coefficient of friction(COF) ranging from 0.08 to 0.17, indicating that it is self-lubricating, whereas the COF of uncoated HSS is 0.1–0.58. With increasing stress, the wear rate of TiB2-Al2O3-Ti(20 %) coating grows from 2.6808 × 10−3 to 4.461 × 10−3 mm3/m, while uncoated HSS wears from 6.4367 × 10−3 to 21.2 × 10−3. The TiB2-Al2O3-Ti(20 %) coating had smooth wear scars having no cracks/debris on the sample surface, indicating that the coated material flowed near the wear scar in a plastic manner.

Friction and Wear Characteristics of Aqueous ZrO2/GO Hybrid Nanolubricants

Aqueous nanolubricants containing ZrO2 nanoparticles, graphene oxide (GO) nanosheets, or hybrid nanoparticles of ZrO2 and GO were formulated using a cost-effective ultrasonication de-agglomeration method. The friction and wear characteristics of these water-based nanolubricants were systematically investigated using a block-on-ring testing configuration with a stainless- and alloy steel contact pair. The concentrations and mass ratios of nanoadditives were varied from 0.02 to 0.10 wt.% and 1:5 to 5:1, respectively, to obtain optimal lubrication performance. The application of a 0.06 wt.% 1:1 ZrO2/GO hybrid nanolubricant resulted in a 57% reduction in COF and a 77% decrease in wear volume compared to water. The optimised ZrO2/GO hybrid nanolubricant was found to perform better than pure ZrO2 and GO nanolubricant in terms of tribological performance due to its synergistic lubrication effect, which showed up to 54% and 41% reductions in friction as well as 42% and 20% decreases in wear compared with 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The analysis of wear scars revealed that using such a ZrO2/GO hybrid nanolubricant yielded a smooth worn surface, with 87%, 45%, and 33% reductions in Sa compared to water and 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The superior tribological performance can be ascribed to the combination of the rolling effect of ZrO2 nanoparticles and the slipping effect of GO nanosheets.

Formation mechanism and wear behavior of gradient nanostructured Inconel 625 alloy

The formation mechanism and wear behavior of a gradient nanostructured (GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment (SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained, nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa (topmost surface) to 2.77 GPa (coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.

Effect of the cycle number on fretting wear behavior of alloy 690TT tube in high-temperature pressurized water

In high temperature water, the fretting wear behavior of Alloy 690TT against Type 405 stainless steel were investigated under different cycle numbers. Results indicated that the change of wear coefficient strongly depended on wear stage and oxide type of compact third body layer (TBL). Within 100000 cycles, the wear gradually entered the stable wear stage from the running-in stage, and the wear coefficient changed conformed to power law distribution. When the number of cycles exceeded 100000, a smooth and compact TBL composing of Fe2O3 and spinel oxide was formed on the surface of the wear scar, the wear coefficient changed slowly. With the increase of cycle number, the percentage of NiCr2O4 and NiFe2O4 in the surface oxide gradually decreased, while that of Fe2O3 gradually increased. The formation of cracks parallel to the surface was related to the surface stress field distribution. During the fretting process, the state of the stress component parallel to the surface changed from tension to compression, prevented cracks from moving to the matrix deep expansion, resulting in the crack propagation direction parallel to the wear surface in the TBL. Finally, the relationship between stable wear life and critical wear depth was established, and the stable wear life was related to running-in wear volume (V0) and stable wear rate (γa).