Tribological Tests Research Articles

Tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement under frictional heat based on molecular dynamics

Abstract Hip prostheses generate higher frictional heat than natural joints at the joint head-socket interface during in vivo service, resulting in higher temperatures of the contact surfaces and surrounding synovial fluid, which affects the frictional properties of the prosthetic material. In order to clarify the influence mechanism of frictional heat on the tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement, the tribological tests of three contact pairs were carried out under different synovial fluid temperatures in this research. Furthermore, the movement processes of the molecular chain structure of UHMWPE during friction were simulated by Materials Studio (MS), and the mechanism of oxidative degradation was discussed. The results show that the temperature of synovial fluid has a significant effect on the friction and wear resistance of UHMWPE and the lubrication characteristics of synovial fluid. At the same time, the action mechanism of the proteins in the synovial fluid that gradually precipitate with the temperature rise to participate in the friction process is related to the friction pair material and contact mode. The synergistic effect of temperature rise and friction will accelerate the oxidative degradation reaction of UHMWPE and form ketone and alcohol oxides on its surface, thus reducing its wear resistance.

The effect of trace solute Au atoms on the phase structure, mechanical and self-lubricating properties of MoSi2 films

To overcome the high friction coefficient and low toughness bottleneck of MoSi2 used as protective films for moving parts, a novel strategy of doping and alloying through magnetron sputtering to build self-lubricating Mo-Si-Au solid solution film has been proposed. Herein, a series of MoSi2 films with different Au contents were prepared, and their phase structure, mechanical and tribological properties were investigated. The results indicate that when Au/Mo atomic ratio R = 0.10, Au atoms tend to replace Si atoms to form Mo-Si-Au solid solution film. Nevertheless, the Au atom would segregate to form a nanocomposite at R = 0.20. The nanoindentation test shows that the Mo-Si-Au solid solution film possesses the largest hardness, which is mainly attributed to the solid solution strengthening. The result of tribological testing exhibits that Au doping can significantly reduce the friction coefficient of MoSi2. More importantly, Mo-Si-Au solid solution film is realized with a lower coefficient of friction (∼0.08), which is ascribed to the formation of MoSiOx lubricating phase during the sliding induced solute Au atoms. Accordingly, the research would provide a considerable theoretical and technical foundation for the development of novel self-lubricating films with excellent mechanical properties.

Tribological Investigation of the Effect of Nanosized Transition Metal Oxides on a Base Oil Containing Overbased Calcium Sulfonate

In this study, copper(II) oxide, titanium dioxide and yttrium(III) oxide nanoparticles were added to Group III-type base oil formulated with overbased calcium sulfonate. The nanosized oxides were treated with ethyl oleate surface modification. The tribological properties of the homogenized oil samples were tested on a linear oscillating tribometer. Friction was continuously monitored during the tribological tests. A surface analysis was performed on the worn samples: the amount of wear was determined using a digital optical and confocal microscope. The type of wear was examined with a scanning electron microscope, while the additives adhered to the surface were examined with energy-dispersive X-ray spectroscopy. From the results of the measurements, it can be concluded that the surface-modified nanoparticles worked well with the overbased calcium sulfonate and significantly reduced both wear and friction. In the present tribology system, the optimal concentration of all three oxide ceramic nanoadditives is 0.4 wt%. By using oxide nanoparticles, friction can be reduced by up to 15% and the wear volume by up to 77%. Overbased calcium sulfonate and oxide ceramic nanoparticles together form a lower friction anti-wear boundary layer on the worn surfaces. The results of the tests represent another step toward the applicability of these nanoparticles in commercial engine lubricants. It is advisable to further investigate the possibility of formulating nanoparticles into the oil.

Abrasion Evaluation of Moon and Mars Simulants on Rotating Shaft/Sealing Materials: Simulants and Structural Materials Review and Selection

Tribological testing of moving shaft/sealing pairs in complex environments is at the frontline of research. Machines working in abrasive conditions are subject to different wear effects. It is not only valid on Earth but especially valid for rovers and future robots used in Mars and Moon missions. The aim of our joint research with the European Space Agency is to study the abrasion phenomena of moving machine elements on Mars and the Moon by using artificial soil samples (“simulants”). This review details mainly the available simulant sources and recommend a selection of the most suitable ones for tribological testing. Moreover, the potential mating structural materials subjected to abrasive space applications are reviewed briefly. The tribological tests are exploring the features of the rotary shaft/seal relationship that is subject to dry friction and intense abrasion. By using the simulants, measurements are performed under laboratory conditions with both a sample test and a real shaft/seal connection. Parameters of the selection criteria were defined, and classification of the simulant sources were made. It was found that simulant particle size distribution and chemical substance content are detailed enough only for a limited type of available artificial Moon and Mars soil samples. Four simulants were identified and applied later in the tribological testing. For the shaft materials, based on a detailed case study of polymers, steel, and aluminum alloys, a high-strength aluminum alloy with a hard anodized surface and a stainless steel were selected for further abrasion tests.

Investigation of mechanical, thermal, and wear‐resistant properties of PDMS nanocomposites filled with low loading of 2D MoS2

AbstractThis study investigates the properties of polydimethylsiloxane (PDMS)‐based nanocomposites with different loadings of two‐dimensional molybdenum disulfide (MoS2) nanosheets. The uniform incorporation of the MoS2 nanosheets in the PDMS matrix was confirmed by unique excitonic absorption peaks, Raman signatures, and x‐ray photoelectron spectra of the MoS2. Owing to the excellent mechanical properties of the embedded MoS2 nanosheets, the elastic modulus and tensile strength of PDMS respectively increased to 42.86% and 19.63% compared to that of pristine PDMS, even at a low MoS2 loading of 0.04 wt%. A dynamic mechanical analysis of the nanocomposites revealed an increase in the storage modulus of PDMS by 9.83% and 30.88% with 0.04 wt% MoS2 loading at strain and frequency sweeps from 0% to 1% and 0.01–10 Hz, respectively. The low MoS2 loading also increased degradation temperature for 50% weight loss from 575.76 (for PDMS) to 652.74°C (for MoS2‐PDMS). In addition, ball‐on‐disk tribology tests revealed that the incorporation of MoS2 nanosheets withstand higher angular speeds (up to 15.71 rad/s) and significantly reduced the friction coefficient by 39.69% (at 7.85 rad/s). Our results imply that MoS2‐PDMS nanocomposites could potentially be used in various applications that require dielectric properties with improved mechanical and thermal stability.

Effect of local pressure difference caused by argon flow on properties of DLC films on rubber

The application of a diamondlike carbon (DLC) coating on rubber surfaces is a promising method to enhance the tribological properties of rubber and alleviate its poor wear resistance. However, in the preparation of DLC films, accurate pressure detection in the sputtering region is challenging due to the single detection position in common sputtering systems. In this paper, the direct current magnetic sputtering method was used to prepare DLC films on nitrile butadiene rubber (NBR). A set of Faraday beam detection device (FBDD) was employed to monitor the current density in the sputtering region. It was found that even if the pressure at the detection position of the vacuum gauge is consistent, the actual pressure in the sputtering region may be different under different rates of argon flow based on the detection results from the FBDD. The surface energy of DLC films was also calculated and researched. According to the results of FBDD, a series of analytical characterization methods were selected to explore the influence mechanism of changing the Ar flow rate on the properties of DLC films on NBR when the initial sputtering pressure remained consistent. The results of FBDD show that the density of the beam in the sputtering region increases with the increase in the Ar flow rate introduced into the vacuum chamber. The surface energy of DLC films was also calculated and evaluated by a contact angle tester. Raman and x-ray photoelectron spectroscopy results indicate that the increase in the Ar flow rate leads to an increase in pressure, which is conducive to the formation of sp3 in DLC films, and the increase in sp3 improves the surface energy of DLC films. The highest sp3 content and surface energy among as-prepared DLC films are observed when the argon flow rate was 40 SCCM. Ball-on disk friction experiment was used to characterize the tribological performance of DLC films on NBR rubber and the adhesion between DLC films and NBR rubber was evaluated by a nanoscratching test. Combining the results of tribology and nanoscratching testing, it can be inferred that the Ar flow rate plays an important role in improving the mechanical properties of DLC films on NBR rubber. Furthermore, the results of scanning electron microscopy confirmed that the sputtering atoms can effectively fill in the grooves of the rubber substrate. This finding is of significance for controlling the sputtering process of preparing DLC on rubber and improving the frictional properties of rubber.

Reduction of Friction and Wear for AISI321 Stainless Steel through Surface Modification Using Nanocrystallization.

Through surface nanocrystallization and low-temperature ion sulfurization, the nanocrystalline/FeS thin film with excellent friction-reduction and antiwear properties was fabricated on the surface of AISI321 stainless steel. The nanocrystallization treatment formed the high hardness and active nanocrystalline structure on the surface of AISI321, with the harness increased from 4.6 GPa to 7.56 GPa. Furthermore, the significantly refined nanostructure strongly increased the concentration of S element in comparison with the single-sulfurized layer on the substrate. Tribological tests reveal that both the original AISI321 substrate and the single-sulfurizing-treated samples are subject to severe abrasion. Single nanocrystallization treatment can improve the wear resistance of AISI321, while the compound treatment can obviously improve the comprehensive tribological properties. The compound-modified layer presents excellent tribological properties with the lowest coefficient of friction (COF) of 0.33, which is related to the increased hardness of the substrate and increased thickness, density, and homogeneity of the sulfurized layer. Furthermore, a physical model is developed for the vacuum tribological behavior of the samples after different treatments. This model provides a reference for revealing the tribological mechanism of the compound-modified layer treated using surface nanocrystallization-assisted chemical heat treatment.

Spectroscopic Evaluation of Surface Chemical Processes Occurring in MoS2 upon Aging.

Molybdenum disulfide (MoS2) coatings have attracted widespread industrial interest owing to their excellent lubricating properties under vacuum and inert conditions. Unfortunately, the increase in MoS2 interfacial shear strength following prolonged exposure to ambient conditions (a process referred to as "aging") has resulted in reliability issues when MoS2 is employed as solid lubricant. While aging of MoS2 is generally attributed to physical and chemical changes caused by adsorbed water and/or oxygen, a mechanistic understanding of the relative role of these two gaseous species in the evolution of the surface chemistry of MoS2 is still elusive. Additionally, remarkably little is known about the effect of thermally- and tribologically-induced microstructural variations in MoS2 on the aging processes occurring in the near-surface region of the coating. Here, we employed three analytical techniques, namely, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and grazing-incidence X-ray diffraction (GIXRD), to gain insights into the aging phenomena occurring in sputtered MoS2 coatings before and after tribological testing, while also evaluating the impact of thermally-induced variations in the coating structure on aging. The outcomes of XPS analyses provide evidence that a substantial surface oxidation of MoS2 only takes place under humid conditions. Furthermore, the correlation of XPS, ToF-SIMS, and GIXRD results allowed for the development of a qualitative model for the impact of shear-induced microstructural variations in MoS2 on the transport of water in the near-surface region of this material and on the extent of surface oxidation. These results add significantly to our understanding of the aging mechanisms of MoS2 coatings used in tribological applications and their dependence on environmental conditions.

Influence of cow dung ash and TiB2 on the physicomechanical and tribological performance of Al6061-based hybrid composites

In order to fabricate a hybrid green metal-matrix composite, the present study investigated the effects of reinforcing a farm waste, cow dung ash (CDA), with hard ceramic titanium diboride (TiB2) of varying weight percentage ratios (0, 7.5:2.5, 5:5, 2.5:7.5 ratio). The physicomechanical and tribological performance were examined and noted that the tensile strength, hardness, and impact energy of the hybrid composites were enhanced with the incorporation of CDA and TiB2 reinforcements. Increasing CDA in hybrid composite reduced the density up to 4.12% and maximum increment in hardness and tensile strength was up to 28% and 24% respectively. The tribology test was conducted on a pin-on-disc tribometer at room temperature with varying loads (10 N–50 N), sliding velocities (0.52 m/s to 2.62 m/s), and sliding distances (500 m–1700 m). The wear loss and friction property of Al6061 has improved with reinforcement's addition and was found to be minimum at 2.5:7.5 (CDA: TiB2) weight percentages. The hybrid composites microstructure and worn surface profile are also associated with the observed tribological outcomes. The obtained results indicated that the S3 hybrid composite showed the best physicomechanical and tribological properties.

Effect of modified MgAl-LDH coating on corrosion resistance and friction properties of aluminum alloy

The in-situ growing approach was utilized in this article to construct the magnesium–aluminum layered double hydroxide (MgAl-LDH) film on the surface of a 1060 aluminum anodized film. To improve the corrosion resistance and friction qualities of aluminum alloy, the MgAl-LDH coating was treated using stearic acid (SA) and thiourea (TU). The aluminum substrate and anodized aluminum film layer corroded to varying degrees after 24 h of immersion in 3.5% (mass) NaCl solution, while the modified hydrotalcite film layer continued to exhibit the same microscopic morphology even after being immersed for 7 d. The results show that the synergistic action of thiourea and stearic acid can effectively improve the corrosion resistance of the MgAl-LDH substrate. The tribological testing reveals that the hydrotalcite film layer and the modified film layer lowered the friction coefficient of the anodized aluminum surface substantially. The results of the simulations and experiments demonstrate that SA forms the dense LDH-TU interlayer film layer by exchanging NO3– ions between TU layers on the one hand and the LDH-SA film layer by adsorption on the surface of LDH on the other. Together, these two processes create LDH-TU-SA, which can significantly increase the substrate's corrosion resistance. This synergistically modified superhydrophobic and retardant hydrotalcite film layer offers a novel approach to the investigation of wear reduction and corrosion protection on the surface of aluminum and its alloys.

Proof of Concept: In-Situ Wear Differentiation of Simultaneously Wearing Counterparts

Accurate assessment of the tribological system’s wear behavior is crucial for optimization. Common tribological test stands rely on a single measurement information—usually the indentation depth of the complete tribological system. If both counterparts experience wear—like polymer–polymer combinations—a subsequent assessment of the tested specimens is needed to estimate the contributions of each partner for determining the wear volume, and thus the wear rate. In this work, we propose a novel approach how an in-situ wear measurement of both simultaneously wearing counterparts can be implemented and generally demonstrate the feasibility on a ball-on-prism tribometer. This is achieved by measuring the system’s indentation depth while simultaneously scanning the ball’s surface with a laser profile scanner, providing information for calculation of the ball’s wear volume. While offering new possibilities for wear evaluation, challenges remain including radial runout of the measured specimen, testing in media and accumulation of large amounts of debris. Overall, this work presents an advancement in the evaluation of wear behavior, enabling better optimization of tribological systems with simultaneous wear. Refinements and adaptations to different setups can further enhance its utility.

Nanohybrid of h‐BN nanosheets supporting CeO2 enhanced epoxy composite coatings with excellent self‐lubricating performance

AbstractPolymer self‐lubricating composite coatings have been widely used on the surface of machinery to extend the life of the moving systems/parts by controlling friction and wear. In this work, epoxy nanocomposite coating with the thickness of about 60 μm was fabricated with addition of hexagonal boron nitride nanosheets (BNNSs)/CeO2 nanohybrid for enhancement in antifriction and wear resistance. The active BNNSs were first obtained by exfoliating h‐BN with alkaline solution, and then the rare earth oxide of CeO2 nanoparticles were immobilized on the surface of BNNSs through hydrothermal method. The microstructure morphology and chemical composition of as‐proposed BNNSs/CeO2 were characterized by field emission scanning electron microscopy, HRTEM, Fourier transform infrared spectroscopy, RS, X‐ray diffraction, and X‐ray photoelectron spectroscopy. And the tribological behaviors of epoxy nanocomposite coatings containing BNNSs, CeO2, and BNNSs/CeO2 were investigated comparatively using ball‐on disc friction tester (MPX‐3). And the 440C stainless‐steel ball with diameter of 8 mm was used as the counterface material. Tribological tests showed that epoxy‐BNNSs/CeO2 had the best friction and wear reduction properties, and the lowest coefficient of friction and wear rate of epoxy‐based composite coating were achieved when the content of BNNSs/CeO2 was 0.5 wt%, with 84.9% and 96.3% reduction, respectively. Moreover, the effect of sliding conditions on the tribological performance of epoxy‐BNNSs/CeO2 was investigated. The corresponding enhancing mechanisms of BNNSs/CeO2 were discussed as well.

Adaptive Neuro-Fuzzy-Based Models for Predicting the Tribological Properties of 3D-Printed PLA Green Composites Used for Biomedical Applications.

Tribological performance is a critical aspect of materials used in biomedical applications, as it can directly impact the comfort and functionality of devices for individuals with disabilities. Polylactic Acid (PLA) is a widely used 3D-printed material in this field, but its mechanical and tribological properties can be limiting. This study focuses on the development of an artificial intelligence model using ANFIS to predict the wear volume of PLA composites under various conditions. The model was built on data gathered from tribological experiments involving PLA green composites with different weight fractions of date particles. These samples were annealed for different durations to eliminate residual stresses from 3D printing and then subjected to tribological tests under varying normal loads and sliding distances. Mechanical properties and finite element models were also analyzed to better understand the tribological results and evaluate the load-carrying capacity of the PLA composites. The ANFIS model demonstrated excellent compatibility and robustness in predicting wear volume, with an average percentage error of less than 0.01% compared to experimental results. This study highlights the potential of heat-treated PLA green composites for improved tribological performance in biomedical applications.

Textured coating or coated texture: Femtosecond laser texturing of a-C:H/WC coatings for dry friction applications

Laser texturing is a well-established method used to customize the tribological performance of PVD coatings. To achieve this enhancement, two distinct strategies can be employed: laser texturing of the substrates prior to coating deposition, or laser texturing of the already deposited coating. Technological and economic problems of tuning laser parameters for different types of substrates can be significantly eliminated by laser texturing of already coated materials. Nerveless, the effect of structural changes caused by laser ablation on friction performance is not well studied. In this work, we investigated the differences in these two strategies on example of commercially available a-C:H/WC gradient coatings. The XPS, FIB, SEM and EDS results revealed that femtosecond laser texturing causes minor oxidation and graphitization of the a-C:H/WC coatings but only in a few top nanometers. Macroscale dry tribological tests reveal no statistically significant difference in tribological performance between samples manufactured using two different strategies irrespective of pattern type and tribotest parameters. This means femtosecond laser texturing of the coated substrates can be implemented in industry as a rapid, cost-, and environment-friendly strategy.

Ultrasonic impact treatment of Ti-based amorphous alloy: Improved tribological performance in air and 3.5 % NaCl solution

The inherent brittleness of amorphous alloys limits their tribological properties. Ultrasonic impact treatment (UIT), applied without preloading, has been used to improve the tribological performance of Ti-based amorphous alloys. Following UIT, the impacted surface softened, whereas the sample cross-section hardened. The change in hardness could be controlled by varying the UIT duration and ultrasonic power. UIT leads to an increase in relaxation enthalpy, suggesting higher free volume and enhanced plasticity. This improved plasticity is evidenced by the Vickers indentation morphologies and the pop-in phenomena of the nanoindentation curves. Regardless of whether the tribology testing was performed in air or in a 3.5 % NaCl solution, UIT led to noticeable reductions in both the coefficient of friction (COF) and the wear rate. The corrosion resistance improved noticeably in both static and sliding states. The primary wear mechanisms were adhesion, abrasion, and delamination. Compared to sliding in air, the COF and wear rate were lower in the NaCl solution. Post UIT, the higher free volume facilitates oxidation in air and the formation of protective corrosion products in the NaCl solution, which is beneficial in reducing adhesion. Simultaneously, the improved plasticity of UIT may contribute to resistance to fatigue and delamination. Therefore, UIT is a simple and feasible method for significantly improving the tribological performance of amorphous alloys.

Anisotropy of the Tribological Performance of Periodically Oxidated Laser-Induced Periodic Surface Structures

Laser-induced periodic surface structures (LIPSS) enable advanced surface functionalization with broad applications in various fields such as micro- and nanoelectronics, medicine, microbiology, tribology, anti-icing systems, and more. This study demonstrates the possibility of achieving anisotropy in the tribological behavior of C45-grade steel structured by nanosecond laser radiation using the LIPSS method. The lateral surface of the steel roller was irradiated with a pulsed Nd:YAG laser at an optimum intensity I = 870 MW/cm2 for the formation of LIPSS. Two sets of samples were formed with LIPSS that were perpendicular and parallel to the roller’s rotational motion direction. The Raman intensity maps revealed that the LIPSS structure consisted of periodically arranged oxides at the top of hills. At the same time, the valleys of the LIPSS structures were almost not oxidized. These results correlated well with scanning electron microscopy energy dispersive X-ray spectroscopy mapping and atomic force microscopy measurements. A comparison of Raman and X-ray photoelectron spectroscopy spectra revealed that both the magnetite phase and traces of the hematite phase were present on the surface of the samples. Tribological tests were performed in two cycles with periodic changes in the normal clamping force and sliding speed. It was found that the LIPSS structures which were formed perpendicularly to the sliding direction on the roller had a significantly greater impact on the friction processes. Structures oriented perpendicular to the direction of motion had a positive influence on reducing the energy consumption of a friction process as well as increasing the wear resistance compared to LIPSS formed parallel to the direction of motion or ones having a non-texturized surface. Laser texturing to produce LIPSS perpendicular to the direction of motion could be recommended for friction pairs operating under low-load conditions.

Enhanced tribological properties of polyimide composite with carbon fiber/graphitic‐carbon nitride nanosheets

AbstractDeveloping polymer self‐lubricating composites is of great significance for reducing mechanical friction and wear. In this study, a hybrid of graphitic carbon nitride (g‐C3N4) nanosheets anchored carbon fiber (CF) was constructed through one‐step calcination method to enhance the tribological performance of polyimide (PI). The presence of g‐C3N4 improved the interfacial interaction of CF/PI composite by endowing CF surface with active sites and rough microstructure. Tribological test results demonstrated that CF/g‐C3N4/PI composite had outstanding antifriction and wear resistance, with friction coefficient and wear rate of 0.209 and 2.23 × 10−7 mm3/Nm, which were reduced by 21% and 73.52% compared to pure PI, respectively. This was mainly attributed to the enhanced interfacial interaction, which was conducive to the stress transferring from PI to CF/g‐C3N4 in sliding process. At the same time, the g‐C3N4 nanosheets could give the composite excellent self‐lubrication property by promoting the formation of transfer film. More importantly, the as‐proposed CF/g‐C3N4/PI composite still maintained good self‐lubricating performance in different sliding environment, with a friction coefficient of 0.132 in water environment and 0.049 in oil environment, suggesting it had a broad prospect in polymer self‐lubricating composite. In addition, the corresponding mechanism was discussed based on the analysis of worn surface of the composite and counterpart.

Tribological Behaviour of 3D printed Polylactic Acid (PLA) Sliding Against Steel at Different Sliding Speed

In this study, the tribological properties of fused deposition modelling (FDM) 3D printed Polylactic Acid (PLA) is studied when it slides against a steel disk at various speeds. 3D printed pins were printed using PRUSA MINI+ 3D Printer according to recommended printing parameters. Pin on disc tribological tests were conducted at normal load of 20 N, sliding time of 20 minutes, and linear sliding speeds of 0.46, 0.58, 0.7 and 0.81 m/s. Experiment results showed that wear rate increases with the increase of sliding speed, and coefficient of friction decreases with the increase in sliding speed. Observation of worn surfaces suggested the major wear mechanisms are abrasion, adhesion, and delamination. The difference in tribological behaviour was mainly caused by hardness-temperature relationship. The main anomaly that occurred in the observed trends are that the pin melted at highest sliding speed, resulting in opposite trends. The increase in temperature at the contact point of the pin and sliding disk weakens PLA pins. Therefore, 3D printed PLA can be used in a temperature-controlled low speed sliding application such as a lubricated gear and not for applications that subjected to high sliding speeds and temperature.

EVALUATION OF THE EFFECTS OF ZDDP AND GRAPHENEADDITIVES IN PAO 8 OIL ON THE TRIBOLOGICAL PROPERTIESOF TIALN COATING

This paper investigates the tribological effects of graphene and anti-wear zinc dialkyl dithiophosphates(ZDDP). Friction tests have been carried out on a tribological tester which operates as a ball and disc assemblyin a frictional, sliding motion. Tests were carried out with a load of 10 N over a sliding distance of 1000 m.TiAlN coated HS6-5-2C steel discs, and 100Cr6 steel balls were used in the tests. Tests were conducted underlubrication conditions with poly()olefin oil PAO 8 with graphene and/or ZDDP. The chemical compositionof the TiAlN coating was studied using a scanning electron microscope, and the wear marks on the discs andballs were observed. The geometric structure of the samples was analysed before and after the friction testsusing a confocal microscope with interferometric mode. The results indicated that the addition of ZDDP andgraphene to the poly()olefin oil had an effect on reducing the friction coefficient.

MECHANICAL PROPERTIES OF POLYMER COATINGSCONTAINING HAP AND ACTIVE SUBSTANCE ON A METALSUBSTRATEWASNOCI

Titanium alloys are currently widely used in implantation, especially in orthopaedics. However, undesirablereactions caused by aluminium and vanadium ions released from the surface of the most commonly used alloys,Ti6Al4V and Ti6Al7Nb, result in the need to modify the surface of the material to improve biocompatibility.Among the available modification methods, one can mention the application of biodegradable polymercoatings, which, apart from improving biocompatibility by limiting the penetration of alloying element ionsinto the tissue environment, can also be a matrix for the release of mineral (HAp) and active substances. Thepaper attempts to determine the mechanical properties of PLGA polymer coatings containing nanoparticlehydroxyapatite and an active substance (dexamethasone) applied with the ultrasonic spray coating methodon a Ti6Al7Nb alloy substrate. The scope of the research included: surface topography testing using an opticalprofilometer, coating adhesion testing to the substrate using the scratch test method and tribological testing(Pin-On-Disc method).