Papers by Keyword: Tribology

Abstract: The aim of this work was an attempt to verify two concepts of cathode modules, and the qualification of structure analysis of nitride coatings with the addition of silicon. The analysis covered one of the most commonly used in industrial conditions AlCrSiN coatings manufactured by the planar ARC and rotating (LARC^®) technology, which have recently gained more and more recognition in the production of coatings by physical vapour deposition (PVD) technique. Their microstructure was examined using transmission electron microscope (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Their mechanical and tribological properties were compared in terms of their application in the field of surface engineering. Tribological tests were performed in sliding friction conditions using the ball-on-disc method, where a ceramic Al₂O₃ ball was used as the counterpart. Presented research results allow to determine the relationship between the structure, wear resistance, and the specific module responsible for the number, type and position of cathodes used in the constitution of the tested coatings. This study complements and contributes to the knowledge on the direct influence of the chemical composition of the coating and the method of its production on the quality and structure of the coated element for wear-resistant coatings produced by PVD in the arc evaporation method (AE).

Abstract: Surface texturing is a process of fabricating specific patterns on a surface to enhance surface properties such as friction, contact area, air aspiration, wear, hydrophobicity, etc. Fabricating surfaces with planned micro features is an effective method to improve tribological performance of the interacting surfaces. Laser surface texturing process is one of the best suitable processes for producing micro-patterns. Micro textures are imparted on HSS discs using CO₂ laser, varying the shape and dimensions of the resulting dimples affecting the frictional coefficient and wear. Experiments have been accomplished to determine effects of textural variations such as areal density of dimples, dimple shape, area of dimples and depth of dimples on the Coefficient of Friction (COF) and Wear. Effects of lubrication conditions (Dry and Wet), pin material (MS, SS, EN31), applied load (25N, 50N, 75N) and Sliding velocity (400 rpm, 800 rpm and 1200 rpm) are evaluated on COF and Wear. Tests have been performed on pin-on-disk apparatus along guidelines of Taguchi L18 Orthogonal Array, keeping constant sliding distance of 940 m (about 10,000 cycles). Experimentally, it is found that wet lubricated, circular shaped dimples, with areal density 7.5%, dimple area 0.09 mm² with MS material pin provides best results. This experimental analysis has been performed to test the applicability, efficiency and reliability of the textured surfaces.

Abstract: The present work investigates the tribological properties of AA6061/1.5 wt.% SiC/1.5 wt.% B₄C hybrid nanocomposites prepared using stir casting technique. The effect of sliding distance, sliding speed and load were investigated on wear rate (WR) and coefficient of friction (COF). Response surface methodology was used to predict and model the responses. Analysis of variance showed that sliding speed and load were the significant factor affecting WR and COF respectively. Desirability analysis was performed for both single and multi-objective optimization. The minimum WR and COF were found to be 0.0015 mm³/m and 0.2430 at sliding distance of 1939.39 m, sliding speed of 1.99 m/s and load of 10 N.

Abstract: Abrasive wear limits the lifetime of key components and wear parts used in various applications. Damage is caused by indentation of harder particles into the wearing materials and subsequent relative motion resulting in ploughing, cutting, and fracture phenomena. The wear mechanisms depend mainly on the applied materials, loading conditions, and abrasives present in the tribosystem, hence material choice is often a difficult task and requires careful evaluation. For this, a variety of laboratory abrasion tests are available of which the scratch test is discussed in this work as the most fundamental abrasive interaction. For further insight into the acting wear mechanisms and microstructural effects, large-scale molecular dynamics simulations were carried out as well as meso-/macroscopic scratch simulations with the mesh-free Material Point Method. The prediction of abrasive wear is of high relevance for industrial applications. Up to now, no general one-to-one match between field application and lab system is known. Here, a simulation-based transfer of experimentally determined wear rates via a lab-2-field approach enables the prediction of wear rates in real applications.

Abstract: Compaction of granular raw materials is a crucial process in modern heavy industries. Extreme operating conditions such as high temperatures, high loads and high press rotational velocities are applied in applications such as hot briquetting processes. For fast and smooth removal from the mold, the adhesion forces are a crucial parameter. To set up a model test for investigations of the adhesive behavior of several release agents under application-oriented harsh operating conditions an available forming tribometer was adapted. Special release agents to reduce adhesive wear and improve the release properties are considered. Surfaces and wear tracks of test samples were characterized by means of optical microscopy, 3D-topographical evaluation as well as SEM analysis. The benefit of the release agents on the subjacent microstructure was evaluated on cross-sections of tribo-stressed areas. Resulting adhesion forces could be well distinguished for all release agents and significant improvements to uncoated operating conditions were achieved. It was proven that the developed test instrumentation is suited to characterize the performance of release agents. The obtained results strongly indicate a significant decrease of severe surface deteriorations when suitable release agents are applied.

Abstract: The travelling waves ultrasonic motors (TWUM) with nonmagnetic, large torque, high precision and simple structure was driven by frictional force, which had been applied aerospace, intelligent and precise instruments. In order to reduce the total weight of TWUM, the phosphor bronze stator with the biggest density among the all parts of TWUM (8.89 g/cm³) were substituted with light weight polymer or polymer composites. This study designed and prepared one types of low density polyimide (PI) composite (1.41g/cm³) reinforced with carbon fibers (CF) which can reduce the weight of stator over 85%. Importantly, this PI composite can meet the main requirements of TWUM, such as high elastic modulus, wear resistance, and suitable friction coefficient. The output stalling torque of TWUM with CF/PI stator still have 0.22 N·m (18.3% compared with TWUM with phosphor bronze stator). Moreover, this study systematically investigated the mechanical and tribological properties of CF/PI composite. For comparison, the pure PI, polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) were also analyzed to reveal the wear mechanisms. The experimental results indicated that CF/PI had better wear resistance and lower friction coefficient than other polymer sliding against Si₃N₄. This light weight polymer composites would be an ideal candidate to reduce the weight of TWUM, which can broaden the lightweight application in the field of aerospace.

Abstract: The results of investigation of mechanical, electrical, thermoelectric and tribological properties of metal-fullerene film composites of Ni-C₆₀ and Ti-C₆₀ systems is presented. It has been found that doping of metals with fullerenes leads to a significant increase in the strength of the material, and a change in the electrical, optical, and other properties of the material. It is established that metal-fullerene films are characterized by low friction coefficients and high wear resistance. It is experimentally shown that metal-fullerene composite thin films possess a capacitive impedance, that the thermopower of Ti-C₆₀ coatings reaches the value of 30 μV/K depending on the Ti/C₆₀ ratio.

Abstract: Within the large scale fusion experimental device ITER, Ion Cyclotron Resonance Heating (ICRH) system is one of the three heating systems which will supply total heating power of 20 MW (40-55 MHz) up to one hour operation. Radio-Frequency (RF) contacts are integrated within the antennas for assembly and operation considerations, which will face extremely harsh service conditions, including neutron irradiation, heavy electrical loads (RF current reaches up to 2 kA with a linear current density of 4.8 kA/m), high thermal loads and also long-duration vacuum baking at 250°C before each experimental plasma campaign. CuCrZr and 316L steel have been shown to be proper base candidate materials for ITER RF contact louvers and conductors respectively. However, in order to limit the wear and the diffusion phenomena at the RF contact as well as to reduce the contact resistance, functional protective layers should be developed. The aim of this work is to investigate Au-Ni and Rh functional layers, electroplated on CuCrZr and 316L respectively. The efficiency of the Au-Ni/Rh coated pairs was evaluated through thermal ageing diffusion tests, using EDS cross-section mapping and XRD techniques. Wear and electrical contact performances of the Au-Ni/Rh original and thermally aged pairs have also been deeply studied on a dedicated tribometer operated at ITER relevant conditions.

Abstract: In our present study, AlB₁₂ and SiB₆ plate specimens prepared by spark plasma sintering AlB₁₂ and SiB₆ powders, respectively, and their tribological properties were investigated in the temperature range of 25°C to 1000°C in air. Also, the micro Vickers hardness of the AlB₁₂ and SiB₆ plate specimens were evaluated in the temperature range of 25°C to 1000°C in an Ar gas atmosphere. It was found that both the steady friction coefficients of the AlB₁₂ and SiB₆ plate specimens were as low as 0.07 to 0.08 at 1000°C. According to XPS analyses, it was found that Al₂O₃ and B₂O₃ films were observed on the worn surfaces of the AlB₁₂ plate specimens after sliding at 1000°C. On the other hand, SiO₂ and B₂O₃ films were observed on the worn surfaces of the SiB₆ plate specimens after sliding at the same temperature. It was also found that both the boride plate specimens exhibited micro Vickers hardness as high as 20 GPa in the temperature range of 25°C to 1000°C.

Abstract: The main objective of this study is to analyze a comparative research about the tribological behavior of Al7075, AISI 1020 and AISI 1045 steels during the ball crater abrasion wear test (Hutchings, 1996) without the presence of lubricants (abrasive slurry). The tests were performed for each alloy with a load equal to 1.4N, during 5, 10, 15 and 20 minutes and the rotation used was equal to 230 rpm. Scanning electron microcopy and optical microscopy were used to characterize the worn samples. The wear resistance was measured by calculating the worn volume (V), with the basis on the diameter of the crater produced by the rotating sphere. [1,2,4]. According to the results, the alloy Al7075 presented the lower wear resistance and the AISI 1020 and AISI 1045 steels obtained a similar wear behavior, probably due to the presence of carbon, which makes the hardness increase. However, when the sliding distance is about 276 m, the wear resistance of AISI 1045 steel falls indicating that AISI 1045 may present lower wear resistance for longer sliding distances