Tribological Tests Research Articles

Structural, mechanical, and tribological properties of CrCN coatings obtained by cathodic arc physical vapour deposition technology at different CH4/N2 gas ratio

Chromium carbonitride coatings were deposited by cathodic arc physical vapor deposition technology at a temperature of 300 °C, as were used the reactive gasses CH4 and N2. The structural analysis of the CrN coating showed a polycrystalline structure with mixed CrN and Cr2N phases. All studied coatings, including the CrC exhibits fcc structure. The phases were confirmed by X-ray photoelectron spectroscopy measurements where a surface oxidation was also detected. The increase of the CH4 gas flow during the deposition process leads to a parabolic trend with the highest hardness of 33.5 GPa for the coating deposited at CH4 / N2 = 0.53. At the same time the lowest coefficient of friction for both counterparts Al2O3 and ZrO2 (0.28 and 0.26, respectively) were measured at CH4 / N2 = 1.86. The tribological tests reveal that the wear of the coatings increases with an increasing CH4 flow rate, whereas the coefficient of friction decreases. This observed contradiction is explained by a phenomenon described as the effect of Rebinder.

Improvement of tribological properties of bearings by laser processing of cast-iron shafts of heavy-duty diesel engines

The article discusses the tribological properties of plain bearing materials in heavy-duty diesel engines with a cast-iron crankshaft. The effectiveness of the influence of laser hardening of shaft necks on the tribological properties of main and connecting rod bearings in comparison with nitriding is substantiated. Simulation comparative tribological tests have been carried out on a laboratory friction machine on samples of materials of an insert made of bronze Br-30 and a shaft made of high-strength cast iron with nodular graphite under conditions of sliding friction with lubrication after laser treatment hardening and nitriding. The influence of hardening treatments of the shaft necks on the antifriction properties and wear resistance of friction couples materials is investigated. Particular attention is paid to the scuff resistance of friction couples. The assumption of a higher efficiency of laser hardening in comparison with nitriding based on the tribological properties of friction surfaces is substantiated. Based on the study, it is recommended to use laser hardening of the crankshaft necks to increase the service life of heavy-duty low-speed diesel engines.

Enhancing the tribological properties of fluoroplastics operating in a hydraulic fluid environment

The issues of an increasing the wear resistance of fluoroplastics under conditions of dry friction against steel and in the environment of hydraulic fluids are discussed in this article. The statement about the prospects of radiation treatment for strengthening fluoroplastics is substantiated. Comparative tribological tests were carried out on a laboratory friction machine according to the friction scheme of the end of a cylindrical sample made of steel 40X13 on a fluoroplastic plate. It has been established that radiation-modified fluoroplastic has increased wear resistance. The antifriction properties of strengthened fluoroplastic during friction in a hydraulic fluid environment are investigated. The influence of load and speed on the friction coefficient is analyzed. Based on the study, a radiation modification of fluoroplastic rod seals of hydraulic cylinders and hydraulic piston machines is proposed, with a possible increase in wear resistance up to 4 times.

Tribological performance of electrically conductive and self-lubricating polypropylene-ionic-liquid composites.

In this work, self-lubricating and electrically conductive polymers on a polypropylene (PP) matrix were prepared and investigated. These properties were obtained by additivating PP with carbon black (CB) and multi-walled carbon nanotubes (MWCNTs), in combination with a surface active ionic liquid (IL, trihexyltetradecylphosphonium docusate [P66614][DOC]). These polymeric composites are expected to achieve coefficients of friction (COFs) comparable to lubricated systems. Combined with electrical conductivity, these materials could be applied in electrically loaded tribosystems. The COF was reduced by up to 25% compared to that of plain PP, and high electrical conductivity and self-lubrication were achieved. Fundamental differences between the carbon-based fillers in their interaction with IL were investigated with high-resolution surface analysis (TEM, AFM) and Raman and ATR-FTIR spectroscopy. By varying the tribological test parameters, the application limits of self-lubrication were identified. It was demonstrated that the contact pressure has a strong influence on the COF. Therefore, this work points to potential applications in (e.g. 3D-printed) bearings and electrically loaded bearings where electrical conductivity and relatively low COFs are required.

Mechanical characterization of tin coatings with biomedical application in elbow prostheses

The present work aims to study TiN films deposited on AISI 316L stainless steel substrates by physical vapor deposition through the Magnetron Sputtering technique with CD, heating it at a temperature of 200º and a constant time of 30 min. Identifying the mechanical properties to be used in biomedical applications, the microstructural characterization was performed by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM). Adhesion tests were performed under the VDI 3198 standard. Tribological wear tests were performed using a 6 mm chromium plated steel pin (AISI 52100) on coated and uncoated substrates to study and compare the sliding effect continuing the same circumferential geometry, with a stroke length of 200 m and a load of 5N in wet and dry way using milli-Q water to simulate biological fluids in order to test the performance and durability of the implant.

EFFECT OF DEEP CRYOGENIC TREATMENT TIME ON MICROMECHANICAL AND TRIBOLOGICAL PROPERTIES OF MAGNESIUM ALLOYS WE43 AND WE54

The paper presents the effect of deep cryogenic treatment time on micromechanical and tribological properties of magnesium alloys, WE43 and WE54. The alloys were subjected to deep cryogenic treatment at a liquid nitrogen temperature (-196°C) for 2 to 48h. Tribological tests were performed in a rotational and a reciprocating linear motion, and wear trace studies were performed by profilometric and microscopic measurements. The tests indicate that deep cryogenic treatment has a favourable effect on the micromechanical, mechanical and tribological parameters of the two investigated alloys. It has also been shown that sub-zero treatment time significantly impacts the cryogenic treatment result. Among other things, there was a nearly 10% increase in hardness, Young's modulus, and a 35% reduction in tribological volumetric wear resulting from the improvement in mechanical properties, as well as a 2-fold reduction in linear wear with an increase in sub-zero treatment time relative to the material in its as-delivered state. Deep cryogenic treatment with appropriately selected sub-zero treatment time allows for improving the service life of magnesium alloys with rare earth metals.

STAND FOR TRIBOLOGICAL STUDIES OF HIP JOINT ENDOPROSTHESIS WITH THE POSSIBILITY OF CHANGING ACETABULUM ANTEVERSION ANGLE AND HEAD ANTI TORSION ANGLE

The article presents the construction of a hip joint movement simulator intended for friction and wear studies of hip joint endoprostheses. The simulator's design enables the fixing of hip endoprosthesis components in accordance with the anatomical structure of the human hip joint. The endoprosthesis head is mounted on a special base in the lower position with a neck-shaft angle of 135°, while the acetabular cup of the endoprosthesis is mounted in the upper part of the mounting head with an inclination angle of 45°. The production of three heads (responsible for the anteversion angle of the acetabulum) and three special bases (responsible for the anti torsion angle of the head) with different fixing angles of the components of the hip joint endoprosthesis made it possible to carry out tribological tests with nine variants of alignment settings. The hip joint endoprosthesis tester is designed to simulate the following movements: flexion and extension, as well as loads occurring in the human hip joint while walking. Thanks to the use of control in the form of electronic cams, the simulator makes it possible to recreate the variable value of the force loading the friction pair as a function of the human walking cycle. The subject of friction and wear studies were hip joint endoprostheses with a head diameter of 44 mm, made of high-carbon Co28Cr6Mo alloy. For each of the nine variants of endoprosthesis component alignment settings, average friction coefficient values were calculated based on the recorded values of the friction torque. The results of the friction and wear studies employing the simulator confirm that the mutual angle alignment setting of the head and the cup has an impact on the value of the frictional resistance occurring in the tribological pair.

THE PROCEDURE OF SELECTING THE VALUES OF THE WORK CONDITION PARAMETERS OF THE BALL-CRATERING METHOD FOR THE ASSESSMENT OF RESISTANCE TO ABRASIVE WEAR

In the example of the CrN coating deposited by the cathodic arc evaporation (CAE) method on two differently prepared substrates, the procedure for selecting the values of the work condition parameters of the ballcratering method was presented. The procedure was developed thanks to applying an individual experiment design from Taguchi's approach and has not been used to determine the values of the parameters of the operating conditions of the test friction node for tribological tests. The procedure, according to Taguchi, allowed us to determine the values of the parameters for assessing the abrasion resistance of anti-wear coatings, with the use of a much smaller number of tests, compared to the methods used so far and a repetitive wear mechanism. The starting point of the presented procedure was selecting the area of the permissible values of the operating parameters, in the ball-cratering method, in which optimal values were searched for to minimise the relative error in determining the diameters of wear marks craters. After determining the area of limit values, an experiment plan was generated in which the variables were: load, rotational speed, minimum friction path, and maximum friction path. The results of abrasive wear tests performed with the ball-cratering method, in accordance with the developed test procedure for the CrN coating – were deposited on the substrate after heat treatment and the substrate after the nitriding process had been successfully verified.

Synergistic Lubrication and Antioxidation Efficacies of Graphene Oxide and Fullerenol as Biological Lubricant Additives for Artificial Joints

The service life of artificial joints has gradually failed to meet the needs of patients. Herein, the synergistic lubrication and antioxidant efficacies of graphene oxide (GO) and fullerenol (Fol) as biological lubricant additives for artificial joints were investigated. The lubrication mechanisms of biological lubricant containing GO and Fol at the friction interface of artificial joints were then revealed. Tribological tests showed that the average friction coefficients of Al2O3–Ti6Al4V pairs and Ti6Al4V–UHMWPE pairs for artificial joints could be reduced by 30% and 22%, respectively, when GO and Fol were used as biological lubricant additives simultaneously. The lubrication mechanism showed that some incommensurate sliding contact surfaces could be formed between the GO nanosheets and spherical Fol at the interface, which reduced the interaction forces of friction pairs. The maximum scavenging rates of •OH and DPPH free radicals by the biological lubricant containing GO and Fol were 35% and 45%, respectively, showing a good antioxidant efficacy of the biological lubricant. This can be attributed to the GO and Fol scavenging free radicals through electron transfer and hydrogen transfer. This study provides a theoretical basis for the development and application of carbon nanomaterials as biological lubricant additives for artificial joints in the future.

Enhancing the Tribological Performance of MoS$$_2$$ Coatings in Humid Environments with the Addition of Bi$$_2$$S$$_3$$

The present work investigates the friction and wear properties of composite Bi\(_2\)S\(_3\)–MoS\(_2\) soft coatings under different humidity levels. To achieve this goal, suspensions containing different proportions of Bi\(_2\)S\(_3\) and MoS\(_2\) were sprayed onto polished SAE 1010 steel substrates to generate soft lubricating coatings. The coatings were subjected to reciprocating sliding tribological tests in air at different humidity levels, between 20 and 80%. Additionally, the formation of tribofilms in dry conditions was evaluated by means of reciprocating tests with increasing total sliding distances. The resulting wear surfaces were analyzed using SEM-EDS, Raman microspectroscopy, and laser confocal microscopy. The frictional behavior of the composite coatings was more stable than that of neat ones. The addition of Bi\(_2\)S\(_3\) to MoS\(_2\) greatly enhanced the durability of the coatings at all the tested humidity levels, reaching up to a 760% increase in their durabilities. This effect depended on the humidity level and the ratio between Bi\(_2\)S\(_3\) and MoS\(_2\).

Artificial Neural Network technique to assess tribological performance of GFRP composites incorporated with graphene nano-platelets

For the present study, glass fibre reinforced polymer (GFRP) composites and GFRP composites incorporated with 0.5 wt% and 1 wt% of graphene nano-platelets (GNPs) were prepared by hand lay-up method, coupled with compression moulding. The tribological testing was conducted in dry-sliding environment with a Pin-on-disc Tribo-Tester for a running time of 10 min and under applied load of 20 N, 40 N, 60 N and 80 N. The experiment data (610 data sets) were used while applying the Artificial Neural Network (ANN) technique. The experiment results were compared with the results obtained from the ANN. It showed that the ANN predicted the output parameters with an overall percentage error of less than 5%. ANN predicted wear for all three composite samples had the mean square error (MSE) less than 2.2005×10−2 and the coefficient of determination (R2) greater than 99 %, whereas the ANN predicted coefficient of friction for all three composite samples had the MSE less than 5.057×10−5 and R2 greater than 90 %. During the course of the present investigation, the Field-emission Scanning Electron Microscope (FESEM) and Energy-dispersive X-ray Spectroscopy (EDS) analysis were also used to examine the wear mechanism.

How to Create Trusted Tribological Characterization Data of Soft Polymers as Input for FEM Simulations?

Soft polymers such as the investigated polyurethane, characterized by low Young's moduli and prone to high shear deflection, are frequently applied in pneumatic cylinders. Their performance and lifetime without external lubrication are highly determined by the friction between seal and shaft and the wear rate. FEM simulation has established itself as a tool in seal design processes but requires input values for friction and wear depending on material, load, and velocity. This paper presents a tribological test configuration for long stroke, reciprocating movement, allowing the generation of data which meet the requirements of input parameters for FEM simulations without the geometrical influences of specific seal profiles. A numerical parameter study, performed with an FEM model, revealed the most eligible sample geometry as a flat, disc-shaped sample of the polymer glued on a stiff sample holder. At the same time, the study illustrates that the sensitivity of the contact pressure distribution to Poisson's ratio and CoF can be minimized by the developed and verified setup. It ensures robust, reliable, and repeatable experimental results with uniform contact pressures and constant contact areas to be used in databases and FEM simulations of seals, enabling upscaling from generically shaped samples to complex seal profiles.

Thermal and Tribological Properties Enhancement of PVE Lubricant Modified with SiO2 and TiO2 Nanoparticles Additive

The addition of nanoparticles may have a positive or negative impact on the thermal and tribological properties of base lubricant. The objective of this paper is to investigate the effect of nanoparticle dispersion in lubricant base in relation to its application in refrigeration system compressors. An investigation of tribological and thermal properties of nanolubricants for rolling piston rotary systems was carried out through four-ball tribology tests and thermal conductivity measurements. Nanolubricants dispersed with SiO2 and TiO2 nanoparticles were tested at various concentrations and temperatures. The changes in thermal conductivity and coefficient of friction (COF) were analyzed while wear weight loss was also calculated from wear scar size. A regression model of thermal conductivity enhancement was proposed for both types of nanoparticles. Zeta potential results show that nanolubricants have excellent stability. The thermal conductivity increases by the increment of nanoparticle concentration but decreases by temperature. The R-square for the regression model is more than 0.9952 with an average deviation not more than 0.29%. The COF for SiO2/PVE nanolubricant at 0.003 vol.% reduced 15% from the baseline. The COF for nanolubricants exceeds the result for base lubricants when the concentration is more than the threshold value. The optimum concentration of SiO2 and TiO2 nanoparticles improved the thermal and tribological properties of PVE lubricant and may offer an advantage when applied to refrigeration systems.

Quantifying the effect of particle characteristics on wheel/rail adhesion & damage through high pressure torsion testing

Low adhesion in the wheel/rail contact is a problem for the rail industry in Great Britain as it causes significant scheduling and safety issues. Applying sand to the wheel/rail contact is used to mitigate against low adhesion however, there is not a consensus on what makes a “good” particle for restoring adhesion, especially with regards to when the particle has entered the wheel/rail contact. The aim of this work was to investigate what particle characteristics had the greatest effect on wheel/rail adhesion and surface conditions, using a process of particle characterisation, tribological testing and statistical modelling. Particle size, shape, and hardness were all found to affect tribological performance. This knowledge can help guide future changes to sanding operations.

Selection of New Heat Treatment Conditions for Novel Electroless Nickel-Boron Deposits and Characterization of Heat-Treated Coatings

Electroless nickel-boron coatings were deposited from a novel deposition bath that was stabilizer-free. Those coatings were analyzed by DSC to determine the crystallization temperature of nickel-boride phases, and then the best heat treatment conditions for the new coatings were selected using the Knoop hardness test and XRD. The results of DSC analysis and XRD were coherent with the findings of previous studies, which shows that the new coating has a boron content lower than 4% wt. The maximum hardness was obtained after heat treatment at 300 °C for 4 h and reached 1196 ± 120 hk50, which is much higher than the as-deposited coating. The heat-treated coatings were then fully characterized using optical and scanning electron microscopy, as well tribological and corrosion tests. Various sliding tests (ball-on-disk and ball-on-flat configurations) were conducted to analyze the coefficient of friction (COF) and wear behavior of the coatings. The maximum von Mises stress was calculated, and values of 624 MPa and 728 MPa were obtained for the ball-on-disk and ball-on flat, respectively, at a depth close to 14 µm from the surface, confirming the suitability of the applied load. Abrasive, adhesive, and fatigue wear mechanisms were observed on the worn sample morphology using SEM. It has been determined that during the corrosion test the OCP and corrosion potential values for the heat-treated coating increase as compared with the as-deposited one, whereas its corrosion resistance decreases.

COATED POLYMERS -A REVIEW

The coating of polymers with different particles has become an important research direction due to the substantial increase in properties and implicitly the use of products in several industrial fields. The objectives of this review paper focus on polymers coating with different ceramic and metal micro particles. Thus, during the first part are presented the main methods of coating (with method detailing, advantages and disadvantages, usage materials and potential industrial applications). After this part the APS - atmospheric plasma spraying technology is detailed because it is one of the most used method. Going forward there are presented some studies from technical literature that analysed different aspects of powders coating onto biodegradable substrates (like polymer) such as structural and morphological analyses, tribological and adhesion tests, corrosion resistance, electrical conductivity, influence of process parameters and their optimization and so on. Thus, the present paper aims to briefly resum researchers' concerns on the coating of polymer-based materials, which has reached in the last period the attention due to their capability and functional applications.

Structure and mechanical properties of MAO coatings formed on aluminum-coated titanium alloy

ABSTRACT Application of titanium alloys is restricted due to their low hardness and poor wear resistance. Duplex surface treatment consisting of depositing of Al coating by arc ion plating (AIP) plus micro-arc oxidation (MAO) was carried out on Ti6Al4V alloy to improve its tribological performance. Ceramic coating mainly composed of α-Al2O3, γ-Al2O3 and mullite was fabricated on the aluminum-coated titanium alloy after the MAO treatment, and its thickness, compactness and hardness increased with the MAO time before the titanium alloy was oxidized. After the substrate titanium alloy was locally oxidized due to oxygen anions inward migration, a thin transition layer containing titanium oxides and aluminum titanate formed and incorporation of Ti in the alumina coating occurred. Occurrence of the strong eruptible discharges at these positions was facilitated probably due to the large difference in permittivity of the alumina and the titanium oxides, which led to the formation of penetrating cracks in the MAO coating. The hardness and compactness of the ceramic coating decreased. Tensile test results showed bonding strength of MAO ceramic coating/aluminum layer/titanium alloy substrate system was more than 40 MPa, and the maximum value could reach around 68 MPa. The bonding strength of the ceramic coating/titanium alloy substrate system decreased to around 34 MPa due to the weak bonding between the alumina ceramic coating and the titanium alloy substrate. Tribological test results show wear resistance of titanium alloy was greatly improved due to the fabrication of hard alumina ceramic coating on titanium alloy.

Theory and experiment of tribological test methods

Based on the analysis of the current state of test methods for wear of friction pairs and the need for methods with certain operating conditions, the problem of developing a theory of test methods for wear of friction pairs according to the ball-cylinder scheme was solved, which makes it possible to determine the parameters of wear models and the general characteristics of the wear resistance of materials. It is shown that the type of wear within the range of properties of the friction pair parameters ensures compliance with the basic conditions in contact: materials, lubrication, pressure, speed, temperature, type of movement, and other less significant factors. It has been established that one of the fundamental issues in the development and conduct of wear tests is to take into account the influence of the stationarity of the wear mode at a point. Test methods in steady and unsteady modes (transient mode) are different. The test method should be based on the solution of the contact problem for a friction pair sample-counter-sample. Based on the solution of wear-contact problem for the "ball-cylinder" scheme, a theory has been developed for identifying the parameters of the wear pattern. To solve the inverse problem, a method of approximating function is proposed and implemented. The power approximation of the experimental function after substitution into the resolving equation gives simple expressions for calculating the model parameters. The results obtained make it possible to predict the intensity of wear of tribocouples under given initial operating conditions: according to loads, sliding speed, characteristics of lubricants and structural materials.

Modified Ni Nanoparticles as Additives in Various Greases: Assessment of Comparative Performance Potential

China’s rapid industrial development requires more energy consumption based on non-renewable energy resources. The energy consumption caused by unnecessary friction accounts for about 4.5% of the GDP in China. Although grease effectively lubricates machines, lubrication failure may occur under severe conditions. Nanomaterials exhibit intriguing tribological performances and have received much attention regarding lubrication. In this study, oleylamine-modified Ni nanoparticles (OA-Ni) were synthesized and used as lubricant additive in four kinds of commonly used greases: lithium, calcium, composite calcium, and polyurea grease. The OA-Ni were uniformly dispersed in the greases through electromagnetic stirring, ultrasonic vibration, and three-roll grinding. The physicochemical properties and the structure of OA-Ni-doped grease were investigated, while the feasibility of OA-Ni as various grease additives at different contact modes was evaluated by a four-ball friction tester and a UMT-tribolab tester. Tribological tests results revealed that the friction-reducing and anti-wear properties of point-to-point contact were increased by 56.7% and 70.3% in lithium grease, respectively, while those of the point-to-face contact were increased by 59.5% and 68.9% in polyurea grease, respectively. The present work provides not only theoretical guidance of nano nickel modification but also a practical reference for the application of modified nanomaterials to various greases.

Environmentally friendly bonded MoS2 solid film lubricants for aerospace applications: Closing the gap

Solid lubricants have been extensively used in the aerospace industry with the main purpose to reduce friction and wear in such demanding environments. One such solid lubricant is MoS2, which is being widely used in tribological applications due to its low friction behavior. This study mainly aims to evaluate the influence of the carrier system (i.e., solvent and water) on the tribological behavior of bonded MoS2 solid film lubricants in order to close the gap with green alternatives. Two bonded MoS2 based solid lubricants were critically evaluated in terms of their tribological behavior, with one lubricant containing a solvent-borne carrier and the other lubricant with a water-borne carrier. The tribological tests were performed using a ball-on-disc tribometer against the alumina (Al2O3) counter face by varying applied load. Ex-situ analysis was carried out using scanning electron microscope (SEM), micro-Raman spectroscopy and Fourier transform Infrared Spectroscopy (FTIR) in order to understand the interfacial processes and chemical composition of the solid lubricants. Overall, the wear rate of both lubricants (i.e., solvent- and water-borne) was equivalent when testing using lower normal loads (i.e., up to 8 N). However, the solvent-borne solid lubricant showed better load carrying capabilities and performed better in terms of the tribological behavior (lower friction and wear) with higher normal loads, which was attributed to the formation of uniform transfer film. The findings of the interfacial phenomenon have provided critical information to further improve the load carrying capability of lubricants without any toxic compounds in order to achieve sustainable environment.