Tribological Behavior Research Articles

Investigating the effect of select alloying elements in additively manufactured Co-Cr alloy for dental prosthetics

Despite the significant advancements in additive manufacturing and its exploration of functionally graded materials (FGMs), the specific roles of W and Mo in enhancing the tribological and corrosion properties of Co-Cr alloys have remained largely underexplored, particularly in the context of dental applications. To address this, CoCrW and CoCrMo alloys were fabricated using the Laser Powder Directed Energy Deposition (LP-DED) process and subjected to a comprehensive suite of microstructural analyses, and tribological behavior followed by corrosion resistance characteristics in an artificial saliva environment. Results revealed that the inclusion of Mo contributes to finer grain sizes, increased hardness and HCP phase stabilization, thus enhancing the wear resistance. Conversely, W's presence in CoCr alloys was found to bolster corrosion resistance which confirms that a synergistic approach of novel alloy development combining W and Mo can be impactful to enhance the overall performance of Co-Cr alloy-based parts. Based on author’s knowledge, this is the first time the effect of W and Mo on additively manufactured Co-Cr alloy has been presented in a comprehensive way combining manufacturing, materials characterization and performance analyses in a context of application in dental prosthetics.

Tribological behavior and biocompatibility of novel Nickel-Free stainless steel manufactured via laser powder bed fusion for biomedical applications

Due to the risk of releasing carcinogenic nickel ions from conventional 316L stainless steel under a corrosive human body environment, a new variant of steel termed nickel-free stainless steel (NiFSS) has been investigated. The present study investigates the tribological properties and biocompatibility of NiFSS manufactured via laser powder bed fusion (PBF-LB/M). The ferritic NiFSS exhibited significantly lower coefficient of friction (0.08 to 0.28) and wear rate (1.60 × 10-6 mm3/Nm to 6.60 × 10-6 mm3/Nm) compared to reported values for austenitic 316L SS, under both dry and simulated body fluid (SBF) conditions and various sliding geometries. This improvement is attributed to the superior hardness (3.394 ± 0.1340 GPa) and elastic modulus (238 ± 9.0797 GPa) of NiFSS. To assess the biocompatibility, the viability of mouse pre-osteoblastic MC3T3-E1 cells was evaluated with an Alamar Blue assay when the cells were cultured on top of PBF-LB/M built NiFSS and 316L SS samples. The results indicated that even though cell growth was most optimal on regular cell culture plastic, cell viability was better maintained on PBF-LB/M built NiFSS compared to 316L SS. Therefore, the results of the present study propose that PBF-LB/M fabricated NiFSS holds promise for application in biomedical devices for joint arthroplasty.

Synergistic lubrication of multilayer Ti3C2Tx@MoS2 composite coatings via hydrothermal synthesis

To reduce wear and energy loss during the movement of miniaturized devices such as wearable devices and MEMS, and to address the inherent limitations of individual categories of solid lubricating materials, a new MXene-based composite solid lubricating material was designed. In this study, Ti3C2Tx@MoS2 composites were successfully prepared via hydrothermal synthesis, with MoS2 nanosheets grown uniformly on the surface and interval of the multilayer Ti3C2Tx. The composites were deposited as a solid lubricant coating on silicon substrates using a drop coating method. Tribological behavior was evaluated by ball-on-disk reciprocating and rotating tribometer, respectively. The results revealed that the friction coefficients of the multilayer Ti3C2Tx@MoS2 composite coatings were reduced by 75%, 69%, and 58%, respectively, compared to the multilayer Ti3C2Tx, MoS2, and their mechanical mixtures. Moreover, this study proposed the excellent wear resistance of the multilayer Ti3C2Tx@MoS2 composite coatings was attributed to the synergistic lubrication of Ti3C2Tx and MoS2. MoS2 was enriched in the wear track, and the tribofilm formed during friction process played the role of friction reduction and lubrication. In comparison, the multilayer Ti3C2Tx had an excellent effect on the wear resistance and structural support.

Fabrication of reinforced Al–Mg composite by TiC particles via FSW: Microstructure and tribology study

In this article, wear and microstructure behaviors of dissimilar Al–Mg joints made by friction stir welding (FSW) with the addition of TiC nanoparticles under different welding parameters were investigated. Optimal joining conditions were achieved by a combination of various rotational and traverse speeds and the best microstructure evolution, mechanical properties, and tribological behaviors were achieved for specimens joined at rotational and traverse speeds of 850 rpm and 50 mm/min, respectively. It was shown that the TiC particles play a prominent role in the microstructure modification and enhanced mechanical properties of weld samples due to the recrystallization process and pinning effect. The maximum hardness and strength values of 241 HV and 168 MPa, respectively were obtained for the weld sample made by optimal condition. The friction coefficient and wear volume loss for weld samples fabricated at 850 rpm and 50 mm/min is comparatively less compared to other conditions due to the highest grain refinement, homogenous distribution of particles, and highest hardness characteristics. The major wear happened because of adhesion, abrasion, plastic deformation, delamination, and oxidation.

A comprehensive study on bioactivity, mechanical and tribological behavior of copper-doped borosilicate glass derived from natural waste for dental applications

The present study investigates in-vitro biomineralization, mechanical, and tribological properties of bioactive borosilicate glass composed of 31B2O3–20SiO2-(24.5-x)Na2O-24.5CaO and xCuO (mol%). Glass was manufactured using conventional melt-quench technique, utilizing chemicals partially derived from bio-waste, with varying copper oxide (CuO) content (x = 0, 1, 3, and 5). In-vitro study was conducted by immersing the specimens in simulated body fluid for 21 days. The formation of apatite layer was confirmed using FTIR, XRD and FESEM-EDS. Vicker's micro hardness tester and a universal testing machine measured hardness and compressive strength, while a pin-on-disc tribometer assessed wear. MTT assay was performed for all the specimens using osteosarcoma MG63 cell line. The study revealed that substituting copper in place of sodium increased the ion dissolution and improved the formation of the apatite layer hence, enhanced the bioactivity, however, accompanied by a gradual decrease in hardness and compressive strength. BSG-0 exhibited the highest hardness (6.64 GPa) and compressive strength (86.81 MPa), while wear resistance weakened with higher CuO content, notably in BSG-5 with the highest specific wear rate (0.072 mm³/N-m) under a 5 N load. Although MTT assay showed non-toxicity for all specimens, except BSG-5, the compounds demonstrated cell tolerance and growth stimulation. In conclusion, the study suggests that CuO-doped borosilicate glasses exhibit superior bioactivity, making them potentially effective for bone filling, wound healing, and dental applications, despite a compromise in mechanical strength and wear resistance.

Mechanical properties and tribological behaviors of Ag/Graphene composite coating under sliding friction and current-carrying fretting

Charging connector of electric vehicles faces two working conditions of sliding friction and current-carrying fretting. Traditional Ag coating is difficult to meet the performance requirements. Herein, Ag/graphene composite coatings were prepared by electroplating, and the chemical compositions, crystal phase, mechanical and tribological properties were studied. The results showed that adding graphene increased the hardness, elastic modulus and toughness. Under sliding friction and current-carrying fretting, Ag/graphene coating exhibited low COF and wear, stable and low ECR. The sliding friction mechanism was dominated by abrasive wear, while the current-carrying fretting mechanism was dominated by adhesive and fatigue wear. The worn surface analysis indicated that the superior tribological properties were attributed to the improved mechanical properties and the formation of transfer film.

Effect of Cryogenic Duration on the Tribological Properties of Sintered Polycrystalline c-BN During Sliding Mating Materials in Vacuum

The service performance of polycrystalline cubic boron nitride (PcBN) tools undergoes significant changes due to the deep space environment to the structure and wear behaviors of PcBN. In this paper, the effect of cryogenic treatment (CT) was studied to investigate the physical and tribological behaviors of PcBN. The hardness and wear resistance of PcBN are improved but wear forms are not affected, which are abrasive wear. The shedding of cBN played the role of micro-cutting edges, carving furrows on surfaces. As the CT duration increases, the wear rate of PcBN decreases from 2.56×10-8 mm3/N mm to 1.61×10-8 mm3/N mm for sliding against Si3N4. When PcBN slid Al2O3, the lowest wear rate is 1×10-8 mm3/N mm which the decline reached 34%. Due to discrepancies in physical and mechanical properties, Si3N4 and YG8 balls exhibit abrasive and adhesive wear, and Al2O3 shows fatigue wear. Until the fatigue failure appeared, Al2O3 exhibited the lowest wear rate of 2.30×10-9 mm3/N mm. Among three materials, the wear rate of Si3N4 was the highest. By calculating the wear rate ratio of the materials, it was concluded that the optimal removal efficiency was achieved for Si3N4 and YG8 when CT duration is 24 and 48 hours, respectively.

High-temperature tribological behaviour and machining performance of self-lubricant CrAlNAg coatings for dry milling operations

Tribological and machining performance of CrAlNAg coatings having different Ag content tested against AISI 1045 medium carbon steel were assessed. Wear track was evaluated by scanning electron microscopy and energy dispersive spectroscopy. 3D topography of wear track and ball counterpart was determined by non-contact type profilometer. The formation of different oxide phases on track was confirmed using Raman spectroscopy. CrAlNAg9 and CrAlNAg12 coatings were found beneficial in reducing material adhesion from counterpart thus providing protective layers to counterpart, whereas small addition of Ag did not provide any improvement on CrAlN coating performance. CrAlNAg9 coated milling inserts demonstrated best results in terms of reduction in chip temperature (~17.5%), cutting forces, surface roughness (~47%) and chip thickness (~12.7%) compared to uncoated inserts.

Advances in hybrid aluminium metal matrix composite produced by stir casting route: A review on applications and fabrication characteristics

The sustained demand for lightweight parts, superior strength, and high-efficiency products has made material researchers interested to study and explore new materials with superior properties. One of the most promising materials for meeting this demand is aluminium metal matrix composite. Due to its tailored properties, the usage of composite is currently increasing in the automotive, aerospace, marine, electronic, defence, domestic, and sports sectors. Simplicity, affordability, and bulk production in the stir casting method have attracted the attention of many researchers across the globe. This paper reviews the need for hybrid aluminium metal matrix composites, various aluminium alloys, and reinforcement materials produced by the stir casting technique. In addition, the applications, morphological, mechanical, and tribological behavior of aluminium hybrid metal matrix composites are discussed. This review will assist materials researchers in selecting the matrix and reinforcements for a specific application of aluminium matrix composites using the stir casting route.

Fabrication and wear behavior of TiC/TiB2-reinforced NiAl intermetallic matrix composites

Combustion synthesis (CS) is a well-known technique for manufacturing intermetallic compounds and intermetallic-matrix composite materials. This research focuses on fabricating NiAl-matrix composites with varying TiC/TiB2 contents as reinforcement, achieved by the combustion synthesis method. The chemical reactions that yield the final NiAl–TiC–TiB2 compounds were interpreted using thermodynamic calculations. The phase analysis and morphology of the composites were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) characterization techniques, respectively. The findings demonstrate that the NiAl matrix contains evenly distributed TiC–TiB2 ceramic-based particles, and no oxidation of reactants occurred during the combustion reaction. With an increase in the TiC–TiB2 reinforcement phases from 0 to 15 wt %, the hardness of the NiAl–TiC–TiB2 product significantly rose from 496 to 1015 Vickers, while the porosity increased from 24% to 39%, attributed to the reduced quantity of melted NiAl available to fill the pores. Examining tribological behavior in synthesized composites involved combining experimental-numerical methods, utilizing sliding wear tests and artificial neural network (ANN) modeling. The wear results revealed decreasing wear rates with reduced loads (from 35 N to 25, and 15 N) and higher TiC/TiB2 ceramic content. Iron traces at C0 and C10 worn samples were 2.47 and 26.18 wt % respectively, which indicates enhanced hardness. The experimental data were used to train and test an artificial neural network (ANN) and statistical analysis revealed a remarkable accuracy of 91% for the ANN model in predicting friction coefficients within SHS-processed composites, as indicated by the R2 value of 0.91 and a MAPE of 6.47.

Exploration on the enhanced mechanism of copper surface tribology by WS2 from MD simulation

This study employs molecular dynamics (MD) simulations with Stillinger-Weber (SW) and Embedded Atom Method (EAM) potentials to investigate the tribological behavior of WS2 coatings on a copper substrate against spherical alumina indenter. Various loads, rotational speeds, and temperatures are explored to analyze their effects on tribological properties. The investigation reveals compelling insights: load-dependent frictional behavior, elucidation of non-linear stress patterns with rotational speeds, and the discernment of temperature-induced alterations in friction coefficient. Furthermore, through detailed analysis utilizing Radial Distribution Function (RDF) methodology, molecular rearrangement dynamics are unveiled, enriching our understanding of the WS2-copper interplay. This research contributes to understanding the intricate dynamics of WS2 coatings and copper interactions, crucial for optimizing tribological performance in practical applications.

The comparative research on tribological behavior of carbon-doped CoCrFeNiV high entropy alloys in air and vacuum environments

In the field of aviation and aerospace engineering, the application of high-entropy alloys (HEAs) is inevitably needs to withstand the damage of both wear and adhesion in vacuum. Herein, the vacuum tribological behavior of a high performance Co21Cr21Fe21Ni21V14.5C1.5 HEAs (C12) were investigated. In this study, the hardness and compressive strength, significantly improved for Co21Cr21Fe21Ni21V14.5C1.5 (1200 °C, C12) HEA compared to the CoCrFeNiV (C0) base alloy. The focus was put on the effect of C element and sintering temperature at 1000℃ and1200 ℃ (C10 and C12) on the microstructure and vacuum tribological mechanisms of the alloy. It was found that the friction coefficient of the C12 alloy under air can be minimized to lower than 0.37. The wear rate of C12 alloy ((1.31-2.67)×10−4mm3/Nm) is 2-4 times lower than that of C10 alloy (2.91-8.31)×10−4mm3/Nm). The wear-resistance of Co21Cr21Fe21Ni21V14.5C1.5 alloy at sinter temperature 1200 °C (C12) is significantly higher than that of alloy sinter temperature at 1000 °C (C10). Therefore, C12 alloy exhibited optimal vacuum tribological properties. This work provides helpful guidance for material design and wear resistance in the field of space tribology.

Influence of Interfacial Tribo-Chemical and Mechanical Effect on Tribological Behaviors of TiN Film in Different Environments

A series of experiments has been conducted to investigate the tribological properties of a TiN film sliding against GCr15 steel balls in ambient air, low vacuum and high vacuum environments. Various friction loads and sliding velocities were also applied. The TiN film displays a steady-state friction stage after the running-in stage in all the above environments, while the durations of running-in stages are different. The steady-state friction coefficients of the TiN film were around 0.56 in ambient air and 0.3 in the high vacuum environment (1 × 10−5 mbar). In the low vacuum (1 × 10−2 mbar) environment, a low friction coefficient (around 0.19) was attained for all the friction tests on TiN film, irrespective of the applied load and sliding velocity. In the meantime, it was noticed that the applied loads and the sliding velocities would change the duration of the running-in stage before reaching the low friction coefficient. It is revealed by the analysis of wear tracks that the metal oxides induced by the tribo-chemical effect at the friction interface play an important role in affecting the tribological behaviors of the TiN films in different environments. The Raman results show that the main component of the metal oxides is hematite (α-Fe2O3), and the amount of iron oxide is related to the friction environment. The composition and quantity of iron oxides produced by the interfacial tribo-chemical effect affect the tribological behavior. The results also show that the mechanical wear process at the friction interface displays a polishing effect, which would reduce the surface roughness. The mechanical wear performance varies under different loads and velocities. The tribological tests results indicate that the interfacial tribo-chemical effect and mechanical wear process should be considered together rather than individually to interpret the tribological behaviors of TiN films in different environments.

Microstructure and tribological behaviors of laser cladded CuAlMnTi–xTiC composite coatings at elevated temperature

CuAlMnTi-xTiC composite coatings were prepared on Ti6Al4V alloy by laser cladding to enhance its tribological properties. The effects of TiC mass fraction on the friction–wear properties of CuAlMnTi–xTiC composite coatings at high–temperature were investigated using an ball–on–disc tester. The results show that the grains of CuAlMnTi–xTiC composite coatings are refined by the addition of TiC, and the metallurgical bonding is formed between the coating and the substrate. The hardness of CuAlMnTi–15%TiC composite coating is higher 1.98 times than that of CuAlMnTi coating, in which the TiC as wear–resistant framework prevents micro–cutting to enhance wear resistance. The average coefficients of friction of CuAlMnTi–0%TiC, –5%TiC, –10%TiC and –15% TiC composite coatings in the stable wear period are 0.465, 0.491, 0.514, and 0.587, respectively, and the corresponding wear rates are 116.8, 111.3, 107.8, and 95.4 μm3•N–1•mm–1, respectively, showing that the wear rate is decreased with the increase of TiC mass fraction. The wear mechanism is transferred from adhesive wear to abrasive wear and slight oxidation wear by the addition of TiC, which is attributed to the improvement of hardness by the refined grain strengthening effect of TiC.

Study of Mechanical and Tribological Behavior of Fly ash with E-Glass fibre Reinforced AL MMC’s

AMC’s specimen made by liquid stir casting technique, by addition of fixed 3% E-glass fibers and fly ash particles in different proportions (4, 6 and 8 wt.%) prepared the matrix phase. A uniform distribution of reinforcement is obtained with good bonding with matrix. Dry sliding wear behavior of the aluminum alloy and the composites has been studied and tested using a pin-on-disc wear and friction monitor. The testing carried out on sliding velocity of 1.5, 2.5 and 3.5 m/s and load ranges from 1, 2 and 3kgf. The composite shows better mechanical properties than the base alloy. Abrasive wear resistance improves by addition of fly ash reinforcement

Mesh stiffness calculation of defective gear system under lubrication with automated assessment of surface defects using convolutional neural networks

As typical failure mode of gear system, the tooth surface pitting, spalling can be detected in most long-running gear system, especially under heavy-load and high-speed condition, or under lubricant-starvation condition, the tooth pitting is characterized by irregular contour and random distribution. Most previous study on the defective gear system mainly based on manually detection of defective region, or just rely on geometric simplification of defects, leading to inaccurate results with low-efficient method, therefore, the machine-vision-based defect inspection method is proposed in the study of defective gear system. First, the pitting defects on gear tooth surface is detected and segmented based on involutional neural network U-net, then the tooth surface with segmented defective region is mapped to the elastohydrodynamic lubrication model of spur gear system, finally, the tribological behavior in addition to the mesh stiffness under lubrication condition of defective spur gear system are investigated and discussed. The results reveal that the machine-vision-based defects inspection could improve the accuracy and efficiency of the failure study for gear system.

In-situ tribo-induced formation of superb lubricious carbon-based tribofilms on the catalytical active MoN-Ag film surfaces

The establishment of environmentally friendly lubrication systems is of significant importance to the sustainable development. Here, we demonstrated an environmentally friendly approach, where superb lubricious carbon-based tribofilms formed in situ originating from base oil through tribochemical reactions, on the surfaces of catalytically active MoN-Ag film. We focused on the study of the tribological behavior of the MoN-Ag/oil solid-liquid system under varying loads. Through detailed characterization analysis of the carbon-based tribofilms, we elucidated the mechanism of friction reduction and wear resistance of the MoN-Ag film in the base oil, as well as the formation mechanism of carbon-based tribofilms. Furthermore, we provided a thermodynamic perspective to clarify the influence of load on the tribo-induced tribochemical reactions within the MoN-Ag/oil solid-liquid system.

Experimental and molecular dynamics simulation based investigation to understand tribological performance of graphene reinforced thermoplastic polyurethane (Gr/TPU) nanocomposites

Ongoing innovative research in tribology aims to develop high-performance polymer nanocomposite (PNC) materials that offer significant improvements in efficiency, reliability, and durability across various engineering systems. Selection of appropriate nanoreinforcements is crucial for maximizing the tribological behavior in PNCs. The primary objective is to investigate how various factors, such as graphene (Gr) loadings, processing techniques, normal loading, and sliding velocity influence the tribological behavior of thermoplastic polyurethane (TPU) and graphene reinforced thermoplastic polyurethane (Gr/TPU) nanocomposites using molecular dynamics (MD) simulation and experiments. Nanocomposite materials fabricated by ultrasonication methods, test specimens are prepared in appropriate dimensions as per ASTM (American Society for Testing and Materials) and DIN (Deutsches Institut für Normung) standard. MD simulations are conducted on the developed plate and rod models under different sliding velocity, pressing and stabbing depth conditions to understand fundamental insights into the friction and wear mechanisms of Gr/TPU nanocomposites at the atomic level. Morphological studies using scanning electron microscopy (SEM) micrographs indicate no case of Gr agglomeration up to 3 wt% Gr/TPU nanocomposite. Energy dispersive spectroscopy (EDS) analysis confirms presence of Carbon (c), Nitrogen (N) and Oxygen (O) in Gr/TPU nanocomposites. Finally the obtained results from MD simulation and experiments show a significant trend of similarity.

Effect of combined laser shock peening and nitrogen implantation on the microstructure and tribology of M50 bearing steel

The M50 bearing steel underwent a combined treatment of laser shock peening (LSP) and nitrogen ion implantation. The microstructure, surface mechanical properties and tribological behaviors were evaluated. Comparative analysis with the untreated sample revealed significant improvements in surface nano-hardness, increasing from 7.51 GPa to 11.35 GPa, 11.51 GPa, and 12.62 GPa for samples subjected to LSP, ion implantation, and combined strengthening, respectively. Correspondingly, surface compressive residual stress showed notable increases from −15.55 MPa to −1043.76 MPa, −451.34 MPa, and −1276.13 MPa, respectively. The improved surface mechanical properties observed in the combined strengthened sample are likely due to the synergistic effects of the combined strengthening. In friction tests, the combined strengthened sample exhibited the lowest friction coefficient, attributed to the presence of a metal nitride layer and a thicker amorphous layer. Wear mechanisms transitioned from fatigue spalling for the untreated specimen to slight wear and the formation of an oxidative adhesion layer after LSP and ion implantation. Remarkably, the surface of the combined strengthened specimen demonstrated minimal wear, with only an oxidative adhesion layer present.

Ultra-low friction system using special wetting interfaces: Bridging across various wetting regimes

Friction was the main way of energy loss in society, and reducing friction has become a focal point in current research. Inspired by special wetting phenomena, an asymmetric multiphase composite (AMPC) friction system was constructed. Tribological behavior of the friction system was evaluated using hydrogel on anodized aluminum as friction pair and superhydrophobic alumina with micro/nano-composite as substrate. Ultra-low friction coefficients (∼10−3) were measured under both Cassie and Wenzel regimes. Especially in Wenzel state, increased contact stress or extended shear rate promoted the formation of transfer lubricant film, thus enabling the ultra-low friction coefficient. Moreover, the system showed mechanical stability during prolonged water lubrication. This novel lubrication approach may provide valuable scientific solutions for specific tribology applications.