Search Results (9)

The influence of ball burnishing on friction and wear at elevated temperatures under fretting conditions has not yet been reported. Fretting experiments were conducted using the Optimol SRV5 tester (Optimol Instruments, Munich, Germany) under dry gross fretting conditions. A ball of WC ceramic was pressed against a disc from the titanium alloy Ti6Al4V. Experiments were carried out at elevated temperatures of 100, 200, and 300 °C. The displacement frequency was 50 Hz, the stroke was 0.1 mm, and the test duration was 15 min. The normal loads used were 40, 60, and 80 N. Ball burnishing led to a substantial reduction in the roughness height and an increase in the microhardness of samples from the titanium alloy. Burnishing, in most cases, caused an improvement in the friction resistance of sliding assemblies. Ball burnishing also led to wear reduction compared to the turned disc sample. The best tribological performance of the sliding pair was achieved for the disc sample burnished with the highest pressure of 40 MPa. An increase in temperature from 100 to 200 °C caused small changes in disc wear volumes and coefficients of friction. A further increase in temperature to 300 °C led to an increase in disc wear rates and friction coefficients. Full article

Alloyed high-carbon steels are materials primarily intended for components operating under conditions of intense tribological wear. The carbides present in the microstructure of these materials significantly contribute to improving the wear resistance of such alloys. However, changes in the morphology of these precipitates can considerably alter the wear rate, leading to a deterioration in the properties of the materials. Therefore, this study aims to analyze the influence of several factors on the tribological wear of alloyed high-carbon steel. The research included friction tests under various load conditions and different sliding paths. Additionally, the samples were subjected to heat treatment to change the morphology of the observed precipitates. The tribological tests were conducted in a block-on-ring configuration under dry friction conditions. The tribological tests were analyzed statistically using analysis of variance (ANOVA). The results of the statistical analysis indicated that the primary factor influencing the observed differences between the samples was the heat treatment time of the material. Additionally, there were no significant statistical differences when pressure and friction path were varied. These findings, in conjunction with the SEM studies, allowed for the evaluation of the wear mechanism. The results demonstrated that, within the adopted tribological system, no alterations in the wear mechanism were observed with changes in test parameters. The observed differences in wear properties between the samples were found to be related to their heat treatment. The heat treatment resulted in alterations to the particle size distribution, with the annealing of the material at an elevated temperature leading to the dissolution of finer particles within the material. An increase in the average diameter of the carbide present in the material was observed to improve the wear resistance of the alloy tested. Full article

In the study, a hybrid lubricant was prepared by introducing graphene into a polyphosphate lubricant. In the tribological test of a steel/steel friction pair at the high temperature of 800 °C, the addition of a small proportion of graphene significantly enhances the lubrication performance of polyphosphate at elevated temperatures. The coefficient of friction and the wear were obviously held down while the surface quality of the high-temperature friction pair was enhanced effectively with the graphene-strengthened polyphosphate lubricant, compared with the dry sliding condition. Through scanning electron microscopy and Raman spectroscopy analysis, the formation mechanism of tribofilm and the antiwear performance of the hybrid lubricant are further explained. This lubricant effectively combines the advantages of both; the combination of polyphosphate melted at elevated temperature with graphene and metal surfaces ensures the self-sealing of the friction contact area and brings better high-temperature oxidation resistance. At the same time, the presence of graphene provides excellent strength to the friction film and ensures the anti-wear and wear-resistant performance of the lubricant at high temperatures. Full article

Titanium alloys and composites are of great interest for a wide variety of industrial applications; however, most of them suffer from poor tribological performance, especially at elevated temperatures. In this study, spark plasma sintering was utilized to produce a fully dense and thermodynamically stable TiB–Ti composite with a high content of ceramic phase (88 wt.%) from self-propagating high temperature synthesized (SHS) powders of commercially available Ti and B. Microstructural examination, thermodynamic assessments, and XRD analysis revealed the in situ formation of titanium borides with a relatively broad grain size distribution and elongated shapes of different aspect ratio. The composite exhibits a considerable hardness of 1550 HV30 combined with a good indentation fracture toughness of 8.2 MPa·m^1/2. Dry sliding wear tests were performed at room and elevated temperature (800 °C) under 5 and 20 N sliding loads with the sliding speed of 0.1 m·s⁻¹ and the sliding distance of 1000 m. A considerable decline in the coefficient of friction and wear rate was demonstrated at elevated temperature sliding. Apart from the protective nature of generated tribo-oxide layer, the development of lubricious boric acid on the surface of the composite was wholly responsible for this phenomenon. A high load bearing capacity of tribo-layer was demonstrated at 800 °C test. Full article

The chromium nitride coating is a hard coating used to improve the sliding friction and wear behavior and is applied to engine components in various operating conditions even at an elevated temperature. In this study, chromium nitride was deposited by a physical vapor deposition process onto the cast iron substrate. All tribological tests were performed on linear reciprocating tribometer with a stroke length of 5 mm in a dry condition at variable temperature levels of 28 °C, 100 °C, 200 °C, and of 300 °C corresponding to loads of 10 N, 20 N, 30 N, and 40 N against the cylinder liner material. The worn surfaces of chromium nitride(CrN) coatings after friction tests were analyzed by scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). The results showed that friction coefficients (COF) ranged from 0.93 to 0.34 from room temperature to 300 °C against the cylinder liner material as a counter-body of 6 mm in diameter; higher temperature results in the positive tribological performance of CrN, with at least 0.34 COF at 300 °C. The wear mechanisms of CrN and counter-body surfaces are abrasive wear accompanied by the slight oxidation. This study guides the wear behavior of cylinder liner coatings in an environment similar to the engine. Full article

The wear evolution of the glass fiber reinforced Polytetrafluoroethylene (PTFE) sliding against duplex steel at elevated temperature was investigated using the interrupted wear tests coupling with the worn surface observations. The morphological changes of the PTFE composite during the sliding were related to the variation of the tribological properties to analyze the underlying wear mechanisms. Results show that the coefficient of friction and wear rate change with the increase of temperature. During the sliding, three regions can be identified regardless of the temperature. The high temperature is beneficial to the formation of tribo-film. The sequence of wear evolution is PTFE removal, load transfer to glass fiber, and minor formation of tribo-film for the low temperature condition. For high temperatures, the wear behaviors are more complicated. The different phenomena include the third body abrasion, flake delamination of PTFE matrix, scratching and reformation of transfer film on the counterface, and the filling of the large scale PTFE groove. These behaviors may dominate the different stages in the stable region, but occur simultaneously and cause the dynamic steady wear. As a result, the wear rate at 200 °C is slightly fluctuant. Full article

In the field of surface engineering, the use of self-lubricous coatings with the incorporation of vanadium represent a promising approach to reduce friction, thus contributing to the wear behavior. For vanadium containing hard coatings produced by means of thin film technology, the reduction in friction at elevated temperatures was repeatedly attributed to temperature-induced and tribo-oxidatively formed oxides which act as solid lubricant. Only very few studies focused on the tribological characteristics of vanadium containing arc sprayed coatings. In this study, the tribological characteristics of a vanadium containing iron-based arc sprayed deposit were investigated in dry sliding experiments under ambient conditions and different temperatures. Types of wear at the worn surfaces and counterparts were examined by means of electron microscopy and energy dispersive X-ray (EDX) spectroscopy. The speciation of vanadium in the superficial layer was determined using X-ray absorption near edge structure (XANES) spectroscopy. It was found that the vanadium-containing coating exhibited a distinctly reduction of the coefficient of friction above 450 °C which further decreased with increasing temperature. XANES spectroscopy indicated an increased oxidation state for the V component on the coating surface, suggesting the prevalence of specific vanadium oxides which promote a self-lubricating ability of the coating. Full article

Dry sliding wear behavior of Mg97Zn1Y2 alloy was investigated at test temperatures of 50–200 °C under three sliding speeds of 0.8 m/s, 3.0 m/s and 4.0 m/s. The wear mechanisms in mild and severe wear regimes were identified by examination of morphologies and compositions of worn surfaces using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), and from which wear transition maps under different sliding speeds were constructed on rectangular coordinate systems with applied load versus test temperature axes. It is found that under each sliding speed condition, mild–severe transition load decreases almost linearly within the test temperature range of 50 °C to 200 °C. Microstructure observation and hardness measurement in subsurfaces identify that the softening effect generating form dynamic crystallization (DRX) is the dominant mechanism for the mild–severe wear transition at elevated temperatures. The mild–severe wear transition at 50–200 °C follows the contact surface DRX temperature criterion, and the transition loads can be well evaluated using the criterion. Full article

Nano-sized ceramic particle reinforced aluminum composites exhibit excellent room-temperature mechanical properties. However, there is limited research on the dry sliding wear behavior of those composites at elevated temperatures, which should be one of the major concerns on elevated temperature applications. Here the Al-Cu composites reinforced with nano-sized TiC_p were fabricated. The dry sliding wear behaviors of the nano-sized TiC_p/Al-Cu composites at various temperatures (140–220 °C) and loads (10–40 N) with different TiC_p contents were studied, and the results showed that the nanocomposites exhibited superior wear resistance. For instance, the relative wear resistance of the 0.5 wt.% nano-sized TiC_p/Al-Cu composite was 83.5% higher than that of the Al-Cu matrix alloy at 180 °C under 20 N, and was also 16.5% higher than that of the 5 wt.% micro-sized TiC_p/Al-Cu composite, attributed to the pronounced Orowan strengthening effect of nanoparticles. The wear rates of the nanocomposites were always lower than those of the Al-Cu matrix alloy under the same test condition, which increased with the increase in temperature and load and with the decrease in TiC_p content. Full article