Low Coefficient Of Friction Values Research Articles

Tribo‐material based on a UHMWPE/RGOC biocomposite for using in artificial joints

AbstractReduced graphene oxide (RGOC) filler that was green synthesized by vitamin C had been included in the ultrahigh molecular weight polyethylene (UHMWPE) matrix to produce biocomposite possessing improved properties especially against wear. The biocomposites filled with different loading (0.1, 0.3, 1.0, and 2.0 wt%) of RGOC was produced by a method of liquid phase ultrasonic mixing and then hot press molding. The structural analysis results of biocomposites showed that RGOC well‐dispersed in polymer matrix and confirmed that there was interaction between the RGOC‐UHMWPE. The biocomposite containing 2.0 wt% RGOC (UHMWPE/RGOC‐2) gave the maximum microhardness and the value increased by 22. 5% compared with unfilled polymer. At the same RGOC content, the biocomposite had the highest thermal stability with residue content at 2.42%. The wear and friction behavior of biocomposites were carried out in a reciprocating friction testing machine under distilled water lubricating conditions. The UHMWPE/RGOC‐2 biocomposite had the lowest friction coefficient value (0.034) and the wear rate of the biocomposite decreased by 44%, compared with that of unfilled UHMWPE. Furthermore, fatigue wear tracks were significantly reduced. This study suggests the use of this composite that had excellent tribological behavior as biomaterial instead of UHMWPE.

Mechanical Properties of Nitrided Layer after Laser Modification

The aim of this work was to study the microstructure and friction coefficient of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Nitriding is well-known technique of thermo-chemical treatment, applied in order to produce the surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. 42CrMo4 steel was treated by composite technology of gas nitriding and laser hardening. The nitriding processes were carried out at temperature of 580 °C for 8h. Next, the nitrided layer was laser-modified using laser TRUMPF TruDiode 3006 with maximal power of 3 kW using the two laser beam powers (P): 0.53 kW and 0.62 kW. Then, the microstructure and properties of the laser-modified nitrided layers were investigated using optical microscopy, Vickers hardness tester and friction wear testing machine. The nitrided layers were subjected to wear tests using a ball-on-disc method at room temperature. The results showed that the microstructure of the produced hybrid layers consisted of the re-melted and heat-affected zones in which martensite mainly occurred. Additional laser treatment effectively increased the hardness, especially in heat-affected zone, as well as the depth of the hardened layer. The layer after modification laser hest tretment were good friction coefficien. The curve of the friction coefficient after the nitrided layer was characterized by large fluctuations. Compared with nitriding technology , the hybrid treatment technology can effectively increase the hardness and wear resistance of the 42CrMo4 steel surface. The effect of LHT on the tribological properties was ambiguous. Although the relatively low value of the average friction coefficient (0.46) was calculated for nitrided layer, the course of friction coefficient was characterized by large fluctuations and the extended grinding-in time. Simultaneously, the course of friction coefficient was very smooth after nitriding and LHT. However, the average friction coefficient were higher, obtaining 0.60 and 0.57 for the hybrid layers, produced using P=530 W and P=620 W, respectively. Keywords: Nitriding; Laser Heat Treatment; Microstructure; Wear Resistance; Microhardness

Tribological behaviour of alternative surface modifications for cold rolling mill rolls

The present work used a new methodology proposed in previous work to analyse the tribological behaviour of coatings/surface modifications with potential to replace the carcinogenic hard chrome still applied in the rolls employed in cold rolling mills. For that, three surface modifications (chromium plating, electroless NiP coating, and plasma nitriding) were carried out on specimens that were previously either ground or surface textured by electrical discharge texturing. The specimens with electroless NiP coating presented the lowest friction coefficients, while plasma nitrided specimens showed the highest. A tribolayer rich in Nickel, Phosphorus, and Oxygen was found for the samples with electroless NiP coating on the surfaces of both the specimens and the counter-bodies, which was apparently responsible for providing low and stable friction coefficient values, as well as reduced wear rates.

Análise do comportamento do par tribológico aço fundido alto C e alto Si contra o metal duro com e sem revestimento de TiN

Aços fundidos com altos teores de carbono (C) e silício (Si) com estrutura bainítica têm despertado o interesse em estudos e aplicações da indústria metal-mecânica, por combinar elevada resistência e alta ductilidade. Essas características são devido à formação de múltiplas fases na sua estrutura, que são ativadas após tratamento térmico de austêmpera. No processo de manufatura desses materiais, etapas de usinagem são implementadas com o material ainda no estado recozido, de modo a facilitar a sua usinabilidade. Aço fundido no estado recozido, têm sido estudados para avaliação da usinabilidade e comportamento tribológico, que auxiliam na seleção mais eficiente de materiais para ferramentas de corte. Sendo assim, este trabalho avaliou o comportamento ao desgaste do metal duro com e sem revestimento de nitreto de titânio (TiN) deslizando contra o aço fundido no estado recozido (270 ±3 HV). Os resultados de pino sobre disco (PSD) indicaram que o conjugado com revestimento apresentou os menores valores de coeficiente de atrito. Entretanto, verificou-se maiores valores de coeficiente de desgaste específico (K) para o conjugado com revestimento réplica. Esse fato foi atribuído ao um possível desplacamento do revestimento TiN. O trabalho contribuiu para o entendimento do comportamento tribológico e a identificação dos mecanismos de desgaste que ocasionaram danos na superfície dos materiais avaliados.

Effect of Applied Cathodic Potential on Friction and Wear Behavior of CoCrMo Alloy in NaCl Solution

Most of the reported work on the effect of applied potential on tribocorrosion or corrosive wear of metallic alloys in a corrosive environment were conducted at anodic potentials. Limited tests have been conducted at cathodic potentials for comparison purposes or to derive the pure mechanical wear component in tribocorrosion. This work investigated the effect of cathodic potential on the friction and wear behaviour of an important biomedical alloy, CoCrMo, sliding against an Al2O3 slider in 0.9% NaCl solution at 37 °C. High friction was found at cathodic potentials close to the open circuit potential, where mechanical wear played a predominant role in material removal. At potentials more cathodic than the hydrogen charging potential, low friction and low wear were observed. The coefficient of friction (COF) and total material loss decreased with increasing cathodic potential, such that at −1000 mV (saturated calomel electrode, SCE), extremely low COF values, as low as 0.02, and negligible material loss were obtained. Such reductions in friction and wear at increasing cathodic potentials were accompanied with the formation of parallel lines in the sliding track and were gradually diminished with increasing applied contact load. It is believed that hydrogen charging and hydrogen segregated layer formation at the surface are responsible for such a phenomenon. It can also be concluded that it is difficult to derive the pure mechanical wear component in tribocorrosion by simply conducting a test at an arbitrary cathodic potential.

Insight into high temperature performance of magnetron sputtered Si-Ta-C-(N) coatings with an ion-implanted interlayer

Challenges related to the application of wear resistant coatings at high temperatures require the development of novel materials with an exceptional combination of mechanical, chemical and tribological properties. The present paper is focused on understanding of relationships between structure, composition and high-temperature performance of the Si-Ta-C-(N) coatings. The coatings were produced using combined magnetron sputtering (MS) and ion implantation (CMSII) technique. It was found that ion implanted coatings demonstrated better thermal shock resistance compared to MS Si-Ta-C-(N) coatings. The Si-Ta-C-(N) coatings revealed a nanocomposite structure consisting of 2–3 nm fcc TaC(N) grains and amorphous a-Si and a-SiC(N) phases. The composition and structure of amorphous matrix and nanocrystallites strongly affected tribological performance of the Si-Ta-C-(N) coatings. The N-doped coatings exhibited exceptionally good tribological performance due to a higher ductility of N-rich amorphous a-SiCN and a-SiNx matrix, and fcc Ta(C,N)-based crystallites compared with the a-Si + a-SiC, and fcc TaC-based phases in N-free coating. The Si-Ta-C-(N) coatings easily withstood oxidation annealing at 800 °C due to the formation of a 200 nm protective TaSiOx amorphous layer. Oxidation annealings revealed that under thin protective TaSiOx layer crystalline components of coatings did not change when Si and C from the amorphous matrix started to diffuse towards the substrate at 800 °C but even after redistribution of elements and formation of oxide scale the coatings demonstrated reasonably high hardness – 13–16 GPa. Triboactivated formation of TaSiOx fibers which could slide/roll against the same TaSiOx tribolayer during high-temperature tribotests resulted in low coefficient of friction values (0.23 at 800 °C) and absence of wear.

Effects of Varying Power and Argon Gas Flux on Tribological Properties and High-Speed Drilling Performance of Diamond-Like Carbon Coatings Deposited using High-Power Impulse Magnetron Sputtering System

This study examines the effects of different pulse powers and gas fluxes on the mechanical and tribological properties and high-speed drilling performance of diamond-like carbon coatings deposited on tungsten carbide substrates by high-power impulse magnetron sputtering. It is shown that an appropriate pulse power is essential in improving the mechanical and tribological properties of the coatings. Specifically, coatings deposited with a pulse power of 5 kW possess a high hardness and good tribological properties, as evidenced by a high hardness-to-elastic modulus ratio. The optimal deposition parameters are determined to be a pulse power of 5 kW and an argon flux of 80 sccm. The resulting coating (designated as C80/5) has the highest hardness (24.95 GPa) of the various coatings and wear rates 11.1, 7.3 and 6.2 times better than those of the bare WC substrate under loads of 6 N, 10 N and 14 N, respectively. Moreover, the coating has low coefficient of friction values of 0.086, 0.098 and 0.062 under loads of 6 N, 10 N and 14 N, respectively. The micro-drilling tests show that the drill coated with C80/5 has a lifetime three times longer than that of an uncoated micro-drill.

Characteristics and high temperature wear behavior of chrome vanadium carbide composite coatings produced by thermo-reactive diffusion

In this study, Cr–V–C composite carbide layers were grown on the surface of a GGG-80 ductile iron using thermo-reactive diffusion (TRD). The TRD process was carried out at temperatures of 900, 1000, and 1100 °C for 1 h using nano-sized FeV and FeCr powders. The coatings were characterized by X-ray diffractometry (XRD), 2D profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), microhardness measurements, nanoindentation, and wear tests. The wear tests were performed on untreated and coated samples using a ball-on-disc type wear tester under 10 N load at four different temperatures (25 °C, 250 °C, 500 °C and 750 °C) against a 6-mm WC ball. Metallographic investigations revealed that the graphite nodules near the surface were dissolved as a result of the TRD process. Depending on the TRD process temperature, a coating with a thickness of 12–36 μm, hardness of 24.14–31.38 GPa, and elastic modulus of 198–233 GPa was obtained. An increase in process temperature increased the thickness, hardness, and elastic modulus of the obtained Cr–V–C layers, which resulted in low friction coefficient values and decreased wear rates. Although all coated samples showed improved wear resistance in all wear test conditions, the wear rates were significantly increased at 750 °C due to flaking.

Mechanical Properties and Corrosion Resistance of Borosintered Distaloy Steels

Distaloy SA is a sponge iron powder (nominal composition: Fe-1.75Ni-1.5Cu-0.5Mo) widely used in the production of powder metallurgy (P/M) parts in the automotive industry. In this study, Distaloy SA powders were sintered in two different atmospheres, one consisting of pure Ar gas (traditional sintering) and the other consisting of a mixture of 90 wt.% B4C and 10 wt.% NaBF4 powders (borosintering). To investigate the effects of the different sintering atmospheres, the P/M samples were characterized using density measurements, surface roughness tests, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, microhardness measurements, nanoindentation experiments, wear tests and corrosion tests. On the surface of the borosintered samples, a 160-325 µm thick double-phase FeB + Fe2B boride layer was formed. The hardness (1405-1688 HV) and elastic modulus (122.21-162.42 GPa) of the surface were significantly improved with the borosintering treatment compared to conventional sintering (215-250 HV, 63.28-94.86 GPa). Borosintering also provided low friction coefficient values and an increased wear resistance compared to conventional sintering. A significant increase in corrosion resistance was also observed with the borosintering treatment in three different solutions. The corrosion rates of both sintered and borosintered samples were ranked as NaCl < HCl < H2SO4. The borosintered samples displayed superior corrosion resistance compared to the sintered samples, especially in the acid solutions. The results of this study show that significant cost savings can be achieved by combining the boriding and sintering treatments in a single borosintering process.

Functionally graded aluminum reinforced with quasicrystal approximant phases – Improving the wear resistance at high temperatures

Functionally graded aluminum was produced and displayed two well-defined metallurgically bonded layers (A and B). Layer A exhibited a ductile Al-matrix (70 HV0.01) reinforced by 53.4 vol% of hard quasicrystal approximant α-Al12(Fe,Mn,Cr)3Si phase (909 HV0.01) distributed homogeneously. Layer B presented the typical structure of a hypoeutectic Al–Si alloy. The tribological behavior of both layers was evaluated in sphere-on-plate configuration at different temperatures: room-temperature, 100, 200, and 300 °C. At room temperature, layer A ensured low coefficient of friction values around 0.2. These values were comparable to those of fully quasicrystalline coatings under dry-sliding testing conditions. The specific wear rate at room temperature of the layer A was about one order of magnitude lower than that of the layer B (1.2 × 10-4versus 2.7 × 10-3 mm3/Nm, respectively), and three orders of magnitude lower at 300 °C (2.3 × 10-5versus 2.8 × 10-2 mm3/Nm, respectively). Improved wear resistance and low friction of layer A were achieved through the formation of a protective and compacted Al-rich oxide layer, where the quasicrystal approximant phase played a critical role. The present results and the discussed wear mechanisms provide significant insights into the development of novel alloys for service in critical components.

Improvement of microstructure, tribology and corrosion characteristics of nickel-aluminum bronze by P/M method

In the present study, we have produced CuAl10Ni5Fe4 alloy powders by using the planar flow casting method. The microstructure, wear response, and corrosion properties of as-cast and P/M parts were systematically investigated, and the improvements by P/M production method were presented. While the as-cast microstructure contained α, β, κıı and κııı phases, the rapidly solidified powders had α, and β’ martensite phases. On the other hand, the lower friction coefficient values were obtained in the case of the P/M production technique in comparison to the as-cast state. Also, an improvement in specific wear rate performances of P/M parts compared with the as-cast alloy was observed. It was observed that the P/M parts exhibited better corrosion properties than the as-cast samples.

Effect of the Degree of Aluminum Doping on the Mechanical and Tribological Characteristics of Titanium–Aluminum Nitride Films

The mechanical and tribological characteristics of titanium–aluminum nitride films deposited by the reactive magnetron sputtering of Ti–Al mosaic targets with different aluminum concentrations were studied. The dependences of the elemental composition, microhardness, and friction coefficient on the degree of doping of the films with aluminum and nitrogen concentration in the Ar/N2 gas mixture during film deposition were obtained. It was found that an increase in the aluminum content in the film results in an increase in film hardness and decrease in the friction coefficient. The optimum nitrogen concentration in the film was achieved at maximum hardness and low values of the friction coefficient. A maximum hardness of 23.5 GPa and a minimum friction coefficient of 0.082 were obtained for films of the composition Ti5AlN1.33, which had a Ti/Al ratio of 5 : 1 and a nitrogen deficiency.

Tribological Investigations on Tool Surfaces for Temperature-Supported Forming of Magnesium AZ31 Sheets.

Aiming to decrease friction coefficient () during the forming of magnesium alloy sheets, nine (9) tools with different hole geometries in their surface (flat, elliptical, and circular) were manufactured from steel Boehler W400 VMR (as known as DIN 1.2343). Tribological investigations were accomplished on a strip drawing machine at 288 °C without lubricants. When compared with a standard tool (surface flat), on average, tools with circular geometries in their surface showed the smallest friction coefficient, while tools with elliptical geometries shown higher. The friction coefficient also was confronted with the ratio between area occupied by holes in the surface of the tool and the total tool surface (i.e., factor f (%)), hole diameter (Ø), and the distance between circle centers (d(c,c)). Principal Component Analysis (PCA) complemented the experimental approach. In summary, both approaches (experimental and theoretical) indicated that the manufactured tool with circular geometries on its surface presented lower friction coefficient values on the forming processes of the magnesium AZ31 sheets.

Characterization of Lubricated Friction Behavior of Thermal Spray Steel Coatings in Comparison with Grey Cast Iron

This work examines friction properties of smooth-honed thermal spray (TS) low carbon steel coatings produced on an Al-9.0% Si alloy using a plasma transferred wire arc (PTWA) method and an AISI 1010 wire used as feedstock in comparison with the ASM type D grey cast iron (CI) samples subjected to the same (smooth) honing process. CI samples prepared using a standard honing process were also tested for comparison. Reciprocating sliding tests were performed using a Cameron–Plint tribometer against CrN-coated counterfaces within a speed range of 0.06–1.20 m/s covering the boundary and mixed lubrication conditions. Stribeck curves were constructed to show the coefficient of friction (COF) variations with the ratio (λ) of lubricant film thickness to composite surface roughness of TS and CI samples at the mid-stroke position where sliding speeds and surface roughnesses were measured. Examination of the Stribeck curves showed that the TS coated surfaces provided lower COF values compared to CI surfaces given the same smooth honing treatment, e.g., for λ = 2.7 a COF of 0.029 was observed for TS and 0.035 for CI, whereas conventional honing of CI provided a COF of 0.047 under the same condition. Metallographic evidence was given for the surface features and formation of tribolayers on the contact surfaces. The arithmetic mean heights of the surfaces, Sa measured after the tests remained similar for the smooth-honed TS and CI samples. The low COF values of the TS samples were discussed in terms of the surface pores generated during their manufacturing process, and the high oil retention depth ratio (Svk/Sk) of the TS coated surfaces due to the presence of these pores.

Sliding wear behavior of AZ91/B4C surface composites produced by friction stir processing

In the present study, the surface of AZ91 Mg alloy was modified by incorporating boron carbide (B4C) particles using friction stir processing (FSP). Sliding wear behavior of these developed AZ91/B4C surface composites was investigated against AISI 52100 steel ball using linear reciprocating tribometer. Hardness tests reveal that the hardness of the fabricated surface composite (∼137.47 HV) is significantly increased compared to the base metal (∼95.5 HV) due to the presence of B4C particles. Wear tests were conducted on the samples at two different sliding velocities; 0.06 m s−1 and 0.12 m s−1. It was observed that at higher sliding velocity of 0.12 m s−1, AZ91/B4C surface composite exhibited lower friction coefficient value in comparison to that of the base metal, whereas it is vice versa at the low sliding velocity of 0.06 m s−1. However, surface composites exhibited superior wear resistance at both the sliding velocities, in comparison to that of the base metal. Scanning electron microscopy and energy-dispersive spectroscopy analysis of the wear tracks were carried out to understand the wear mechanisms. From the observations, a combination of abrasive, adhesive, and oxidative wear mechanisms were found to be prominent.

Numerical Study on Subsurface Stress in Hertzian Contacts under Pure Sliding Conditions

In this study, the two-dimensional numerical simulation on the subsurface stress field in Hertzian contact under the pure sliding condition for different speeds and coefficients of friction is presented. The Hertzian contacts are represented by a dry contact between a rigid flat surface and an elastic cylinder with radius R=12.5 mm. Simulation is carried out through two steps, the first one is for applying normal load and the second one is for applying angular speed for the cylinder. The results of subsurface stress filed for pure sliding are compared to non-moving Hertzian contact. The results show that pure sliding speed has a major effect on the value of maximum von Mises stress in the subsurface of contact. The effect of sliding speed is attributed to tangential forces and elastic deformation in the contact. On the other hand, the coefficient of friction has a primary effect on the position of maximum stress and the shift of the contact region. Indeed, when pure sliding motion is introduced with a low value of friction coefficient, the shift of the contact region is negligible compared to non-moving Hertzian contact. The study is extended to investigate the effect of contact geometry on subsurface stress for Hertzian contact in the cam-follower interface. The shape of the follower has a significant effect on the value and distribution of Hertzian stress, thus, the fatigue life of rubbing surfaces of the cam-follower interface.

Properties and High Temperature Dry Sliding Wear Behavior of Boronized Inconel 718

Silicide-free boride layers were grown on Inconel 718 Ni-based superalloy surface at 850 °C, 950 °C, and 1050 °C for 2, 4, 6 hour by the powder pack-boronizing process using nano-sized B4C powders. The coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 3D profilometry, and microhardness measurements. Wear experiments were carried out on untreated and boronized Inconel 718 using a ball-on-disk tribometer under dry sliding conditions at temperatures of 25 °C, 400 °C, and 750 °C. An increase in boronizing temperature and duration increased the thickness and hardness of the obtained boride layers, which resulted in low coefficient of friction values and decreased wear rates. Scanning electron microscopy images of the worn surfaces revealed two-body abrasion as the effective wear mechanism in the untreated samples, and three-body abrasion assisted by microcracking and spalling as the dominant wear mechanism in the boronized samples. A transition from mild to severe wear occurred in the untreated samples, while wear rates remained low in the boronized samples up to 750 °C. In conclusion, boronized Inconel 718 was capable of sustaining its boride layers under 5 N for 1800 m at wear-test temperatures up to 750 °C.

Low friction and wear properties of carbon nanomaterials in high vacuum environment

Abstract Promoting the application of carbon nanomaterials in space has special significance because their excellent electroconductivity can provide pathways to eliminate electrostatic accumulation as compared with the traditional space solid lubricant such as MoS2. Herein, tribological behaviors of graphene and C60 are investigated by a ball-on-disk tribometer in vacuum environment. The morphology and chemical composition of worn surface are examined by TEM and Raman spectra. Experimental results show that graphene and C60 exhibit low friction coefficient value of 0.018 and 0.125, respectively. Friction-induced ordered structure is account for the excellent friction behavior of graphene, while the special sphere structure enables the good wear resistance of C60. The present study helps to understand the lubrication mechanism of carbon nanomaterial in vacuum.

Transport and diffusion of Brownian particles in a tilted deformable potential

The underdamped Brownian motion of particles in a deformable potential in response to a constant external force is investigated. Using the matrix continued fraction method, we compute the diffusion coefficient of Brownian particles via the dynamics factor structure at low temperature and intermediate values of friction coefficient. It is numerically found that the transport properties of Brownian particles such as the effective diffusion coefficient, the average velocity and the distribution probability are sensitive to the shape parameter r of the modified nonsinusoidal Remoissenet–Peyrard deformable potential. The bistable behaviour and the distribution of velocity which also shed light on the diffusion anomalies are discussed for some values of the shape parameter. We show that for the negative values of the shape parameter (r<0), the average velocity versus the external tilting of Brownian particles is optimized, while for the positive values (r>0), the average velocity of Brownian particles collapses due to the geometry of the system combined with the friction. Finally, the mechanism of enhancement of the effective diffusion coefficient for a range of the external force is discussed as a function of the shape parameter. We find a power law for the effective diffusion coefficient in terms of the shape parameter r, and show that, it evolves as Dth∼∣r∣2.

The Effect of Boron Nitride on Tribological Behavior of Mg Matrix Composite at Room and Elevated Temperatures

Abstract The goal of the study is to examine the dry sliding wear behavior of pure Mg and Mg/nano-boron nitride (BN) composite at elevated temperatures. The wear behavior of the samples was evaluated under loads of 5, 10, and 20 N, at sliding speed of 80, 130, and 180 mm s−1 and at temperatures of 25, 100, and 175 °C. The examination of worn surface, counterface, and wear debris was performed. The results showed that nano-BN particles lead to substantial enhancement of wear resistance for both room and elevated temperatures. Mg/0.25 BN has lower coefficient of friction values due to the presence of BN which act as solid lubricant. The wear mechanisms are thermal softening, melting, oxidation, abrasion, and delamination.