Tribological behavior of five different surfaces patterns, bioinspired from maize leaf skin, shark skin, snakeskin, pitcher’s structure and lizard skin, was investigated. Bioinspired surfaces have ...been printed using Fused Deposition Modelling (FDM) technology from a marked Poly Lactic Acid (PLA). Tribological tests were carried out using a reciprocating sliding device under dry conditions at room temperature. Particular interest was given to the investigation of the friction anisotropy as well as the wear mechanisms. The correlation between the apparent friction coefficient and the test conditions, particularly, the 3D printed bioinspired surface patterns and the number of cycles, was emphasized via the friction maps.
In this study, two asymmetric texturing forms are proposed and a numerical optimization with a genetic algorithm is conducted for the asymmetric surface texturing to improve lubricant load support ...under reciprocating sliding conditions. Considering the two stroke performances in a reciprocating motion, four evaluation criteria are used to control and enhance the directional or overall performance of the surfaces with the optimized textures. The effects of operating conditions on the optimal texturing are also highlighted. The results show that the well-designed asymmetric texturing has the potential to improve the overall performance or achieve directional frictional control, and the optimal texturing is not necessarily symmetric or asymmetric and should be designed based on its operating condition and practical demand.
•Two asymmetric texturings are introduced on the reciprocating surfaces to achieve directional/overall performance control.•A numerical method with a genetic algorithm is proposed to optimize the asymmetric surface texturing.•Evaluation criteria are used to control and enhance the directional or overall performance of the optimized textures.•The effects of operating conditions on the optimal texturing are highlighted.
WC-based composites are extremely resistant to wear and corrosion; they are used in numerous mechanical applications (e.g., pumps, valves, mechanical seals, flow control technology, etc.). They are ...generally produced by sintering tungsten carbide with a metal binder (cobalt is the most common). However, Co is part of the 2017 list of 27 critical raw materials with a high supply-risk and economic importance to which reliable and unhindered access is a concern for European industry and value chains. This paper aims at the mechanical and tribological characterization, by reciprocating sliding wear experiments and scratch tests, of new and innovative cemented carbide grades that contribute to the reduction/substitution of critical materials like the Co binder. It was found that Co plays an important role in the wear behaviour of hardmetals. On the other hand, the composites developed present wear rates close (although higher) to WC-Co, constituting valid alternatives for wear parts.
•Effect of different binders on the sliding wear resistance of WC-based composites.•Scratch tests were carried out to better understand the tribological behaviour.•Wear mechanism of abrasion is present in all tested specimens.•Co binder plays a leading role in the wear behaviour of cemented carbides.•The developed composites constitute valid alternatives for wear parts.
The aim of this work was to study the abrasive and reciprocating sliding wear resistance of four commercial resin composites for dental restorations. Resin composite samples were divided into four ...groups considering the different materials and then separated for compressive, abrasive and sliding tests (n=10). Micro-abrasion tests were performed against a stainless steel rotating ball on 3N normal load for 300 revolutions in the presence of a suspension containing a commercial whitening and abrasive toothpaste. Reciprocating sliding ball-on-plate friction tests were performed against an alumina ball on 20N normal load at 1Hz in the presence of artificial saliva at 37°C for 30min. The wear volume was evaluated for the different groups of resin composites and correlated with their mechanical properties and inorganic composition in terms of size and volume percentage of filler particles. Resin composites with high volume content of inorganic fillers (82wt%) consisting of micro particles (0.1–2.5μm) combined with small nanoparticles (20–60nm) revealed the most proper mechanical and tribological response. The dominant wear mechanisms consisted on fine micro-scale abrasion for abrasion tests and surface fatigue and abrasion for reciprocating sliding tests.
•Micro-abrasion and wear sliding tests were performed on dental resin composites.•A high volume of fillers increased the tribological response of the composites.•Surface fatigue and abrasion was detected after wear sliding tests.
A MoSi2/TiC/γ-Ni high temperature wear-resistant composite coating was in-situ synthesized on AISI 321 substrate by co-axial powder feeding plasma transferred arc (PTA) cladding process using powders ...blend of Ni, Ti, Mo, Si and Ni-P coated graphite as raw material. Microstructure and in-situ synthesis mechanism of the composite coating was analyzed. High temperature tribological properties of the coating were evaluated. Test results show that the composite coating has refined microstructure consisting of MoSi2, TiC and γ-Ni. TiC and MoSi2 as in-situ synthesized reinforcing phases are uniformly scattered in the γ-Ni/TiC binary eutectic matrix. Benefiting from the unique microstructure, the coating exhibits high hardness, low and stable friction coefficient values and good high temperature reciprocating sliding wear resistance.
•TiC/MoSi2/γ-Ni composite coating is in-situ synthesized by PTA cladding.•The coating has refined microstructure and good metallurgical bond.•In-situ synthesis mechanism of the composite coating is discussed.•The coating has high hardness, low and stable friction coefficient.•Due to novel structure, the coating exhibits good high temperature wear resistance.
This paper investigates why the static friction peak is mostly absent in reciprocating sliding and gross-slip fretting literature. Here, reciprocating sliding tests were conducted on ultra-smooth ...silicon surfaces. A prominent static friction peak was present in the initial cycles. However, a rapid wear-induced decay in the static friction peak occurred after the first cycle with the peak being mostly absent by about 30 cycles. Two possible explanations are proposed for the wear-induced decay: (1) that increasing surface roughness (with cycles) reduces the fully stuck contact area and (2) that wear reduces the bonding strength of the stuck interface by removing third body contaminant molecules. Predictions from a multi-asperity friction model are used to support these arguments.
•Existence of the static friction peak in reciprocating sliding investigated.•Reciprocating sliding tests conducted on ultra-smooth silicon surfaces (Rq 0.32 nm).•Peak is present in initial cycles, but undergoes rapid wear-induced decay.•Multi-asperity friction model implemented for comparison with experiments.•Wear-induced decay explicable by either roughness changes or chemical changes.
The UHMWPE wear debris has become an important reason affecting the service life and clinical reliability of the prosthesis. In order to further reveal the wear debris characteristics, three kinds of ...UHMWPE materials including non-crosslinked UHMWPE (UPE), Crosslinked UHMWPE (XLPE) and E-vitamin doped UHMWPE (EXPE) were taken as research objects, and the quantity, size, morphology and distribution characteristics of wear debris under reciprocating sliding and compound motion modes were systematically studied. Among them, the ball-on-disk samples were adopted under reciprocating sliding, and the real ball-on-socket contact mode of artificial cervical disc prosthesis was adopted under compound motion. The tribological experiments were performed with the frequency of 2Hz under 50,000 cycles with newborn bovine serum solution. The results showed that the dominant wear mechanism was abrasive wear accompanied by fatigue cracks under reciprocating sliding mode, while adhesive wear accompanied by a few abrasive wear under compound motion mode. Compared with the quantity of wear debris under reciprocating sliding mode, the number of UHMWPE debris under composite motion mode was reduced by 28.8%, 31.4% and 37.1% for UPE, XLPE and EXPE debris, respectively. The debris results of the three different polymers were consistent in the quantity, size range, morphology and distribution, but different in the size distribution characteristics. The largest proportion of EXPE debris size occurred in the range of less than 1 μm, while the largest proportion of UPE and XLPE debris size ranges from 1 to 5 μm under reciprocating sliding mode. When the debris size was in the range of 1–5 μm under compound motion mode, it accounted for the largest proportion with a value of 55.7%, 66.7% and 74.0% for UPE, XLPE and EXPE debris, respectively. The UHMWPE debris morphology included six main types: spherical, flakes, rods, fibrillar, granular, and other types. Granular and “other types” debris were the dominant types and the sum proportion of these two types of debris for the three kinds of UHMWPE materials was all as high as 80%. Hence, the material type, pair shape, load and movement profiles may have more or less influence on the quantity, size, morphology and distribution characteristics of UHMWPE debris.
•Debris of three PE under two motions was studied.•Quantity, size, morphology and distribution of debris were studied.•Debris quantity was reduced under composite motion.•Size distribution was different for three polymers.•1–5 μm debris accounted for the largest proportion.
The presence of hard, brittle, thin White Etching Layers (WELs) on rail surfaces plays a critical role in varying the tribology behaviours at the wheel and rail interface. The reciprocating sliding ...tests were carried out on the rail samples covered with two types of WELs, including thermomechanically-induced WEL (TP-WEL) and mechanically-induced WEL (SD-WEL) at room temperature and 600 °C. A WEL-free rail sample was also employed for the comparison. The wear mechanism of WEL-free rail shifts from severe abrasive wear at room temperature to adhesive dominant wear at 600 °C. Under the pressurized sliding conditions of 1.2 GPa at 600 °C, the WEL-free rail was observed to form WEL and BEL. The pre-existed SD-WEL and TP-WEL on the rail samples could transform into worn WEL at the topmost contact rail surface with Brown Ething Layer (BEL) formation beneath it. The formation of BEL is attributed to the tempered effect on pre-existed WEL. Due to their high hardness, both SD-WEL and TP-WEL-covered rails exhibit minimal abrasive behaviours at room temperature while displaying adhesive dominant wear mechanisms at 600 °C. Of the two types of WELs, TP-WEL has lower wear resistance, whereas SD-WEL promotes high friction and reduces wear loss.
•Tribological behaviours of two distinct classes of White Etching Layers (WELs) on the rail surface were measured.•Tribological properties of the rail are dependent on the existence and type of WELs and the temperature at rail surface.•The pre-existed WELs could be transferred into worn WEL at the topmost contact and underlying Brown Etching Layer (BEL).•In comparison with mechanically-induced WEL, thermomechanically-induced WEL is more prone to be worn out during service.
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