查看更多>>摘要：Highly loaded wear components in manifold applications such as sieves, crushers, etc. suffer from combined impact and abrasive wear. To gain deeper understanding of different ongoing mechanisms, four different Fe-based materials, two martensitic steels Hardox 450 and Hardox 600, and two gas metal arc welded (GMAW) hardfacings - a Fe–Cr–C based hardfacing and a complex-alloyed Fe–Cr–Nb–C–B alloy were investigated with a novel modification of a cyclic impact and abrasion test. This test rig uses quartz sand as abrasive and a plunger simulating industrial sieving applications. Pre- and post-test materials analyses were performed utilising 3D microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), microhardness and nanoindentation tests for a thorough materials analysis and the clarification of the main occurring damaging mechanisms. Results indicate a very beneficial performance of a complex-alloyed Fe–Cr–Nb–C–B alloy due to its fine-dispersed hard phases and their homogenous distribution throughout the material, which does not change much with varying deposition parameters. In comparison, higher wear rates of a hypereutectic Fe–Cr–C alloy are attributed to coarse precipitated Cr-carbides within the microstructure. At martensitic steels, mechanically mixed layer were formed in the impact-abrasion region, which decreases the wear attack to a certain extent. However, massive materials displacement and abrasive wear occurs due to the lack of hard phases and high ductility, which obstruct increased abrasive attack.
查看更多>>摘要：NiHard-4 and high-Cr-Mo white cast irons are two classes of abrasion-resistant cast irons extensively utilized in mining and related industries. Despite widespread usage, systematic performance comparisons between the two classes are lacking. Using four exemplar NiHard-4 and four exemplar high-Cr-Mo WCIs, this study compares the abrasive wear performance of the two alloy classes under a variety of conditions. The wear tests were the dry sand rubber wheel abrasion test (DS-RWAT), inner circumference abrasion test (ICAT) with quartzite, and ICAT with basalt. The resulting quantitative trends were interpreted and explained using bulk hardness, microhardness and nanohardness measurements, coupled with SEM of microstructures and worn surfaces. In all three abrasion tests the average wear life of high-Cr-Mo WCI was superior to NiHard-4. Average life improvements were 20% in DS-RWAT, 77% in ICAT-quartzite and 124% in ICAT-basalt. In the DS-RWAT there was overlap in the data and the difference between the two alloy classes was not statistically significant, but in the ICAT, for both rock types the two classes were strongly differentiated. Of various hypotheses considered to explain the results, the experimental evidence required that differences in carbide volume fraction or matrix hardness must be rejected. Instead it was shown that the superior performance of high-Cr-Mo WCIs was due primarily to their higher Cr:C ratio, resulting in higher Cr:Fe ratio and therefore elevated hardness and fracture toughness of the eutectic carbides.
查看更多>>摘要：The longitudinal vibration of the multi-layer winding hoisting wire rope is inevitable due to the time-varying dead weight and the fluctuation of hoisting acceleration. Longitudinal vibration will lead to relative sliding between the hoisting wire rope and the rope groove, resulting in friction and wear, and thus threaten the service life of the wire rope. In order to investigate the influence of longitudinal vibration on the tribological characteristics of the wire rope and its wear mechanism, the friction and wear tests between the sliding wire rope and the fixed wire rope groove under different longitudinal vibration amplitudes and frequencies were carried out with the help of a self-developed test rig. Results show that the coefficient of friction (CoF) of the wire rope has experienced three stages of rapid growth, “concave” transition and relative stability with the increase of sliding distance, which increases first and then decreases with increasing the amplitude in the relatively stable stage and has no obvious change with an increase in the frequency. Additionally, the maximum temperature rises at the wind-out region of the sliding wire rope and the middle of the contact wire ropes increase first and then decrease with the increase of the amplitude in the relatively stable stage, but increase gradually with an increase in the frequency. The vibration intensities in the wear regions of the wire ropes have a great increase in the rapid wear stage. Furthermore, the main vibration wear mechanisms of the wire rope are abrasive wear and adhesive wear, the content of O element in the furrows and the abrasive adhesion regions are higher, and the frequency has less effect on the oxidation degree of the worn surface of the wire rope than the amplitude.
查看更多>>摘要：High-speed machining of austenitic stainless steel normally causes significant tool damage and generates reduced tool life. In this paper, five AlTiN PVD coatings with different Al/Ti atomic ratios (50/50, 60/40, 67/33, 70/30 and 73/27) which deposited on cemented carbide inserts were used to conduct high-speed of 370 m/min finish turning tests. The experiments were carried out under different cooling conditions (dry and wet) on SS304 to study the tribological behavior of the AlTiN coatings with different Al/Ti ratios and the effect of the coolant under such aggressive cutting conditions. During the experiments, tool life, cutting force, wear mechanism, friction condition and surface integrity of machined workpiece were investigated. Crater wear was found to be the predominant wear mode during the cutting test, while the complex combination of oxidation, abrasion/attrition, adhesion, and chipping contributed to the tool failure. Given the machining conditions proposed in this study, the results revealed that all coated inserts possessed an improved friction behavior in the wet cutting condition. Compared to the dry machining, all five coatings had exhibited 2–3 times longer tool life. The AlTiN coated insert (Al/Ti = 60/40), in particular, exhibited a cutting length of almost 7000 m, compared to 1000 m for the AlTiN coated insert (Al/Ti = 73/27).
查看更多>>摘要：The aim of this research work is to develop and compare in-house Ti-based coatings with commercial coatings for cermet tools, specifically for the high-speed dry turning of Austenitic stainless steel (AISI 304). In the present study, commercial Ti-based coated cermet tools from different manufacturers are used to evaluate and compare the performance of commercial coatings. This research focuses on the investigation of the performance for the various commercial coatings on cermet tools based on the mico-mechanical properties, tool performance and surface roughness. The results are used to develop a range of in-house Ti-based PVD coatings with different compositions and compare their performance with similar commercial coatings. Coating surface topography and structure were investigated using Atomic Force Microscopy (AFM). The compositions of coating materials and tribo films were determined using Energy-Dispersive X-ray Spectrometry (EDS) and X-ray photoelectron spectroscopy. The results of this research demonstrate that the compositions of various coatings affect the micro-mechanical properties and significantly influence the tool life and wear morphology. The performance of in-house Ti-based coatings with a similar composition to commercial coatings were better than the latter, depending upon their micro-mechanical properties.
查看更多>>摘要：Cycling contact fatigue indentation tests in dry and wet conditions were conducted in cemented carbides CVD-coated with Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 systems. In dry contact experiments, all imprints presented a deformed area where the coating was still present after the test. Formation of cracks was visible at the edge of the contact point of the imprint. On the other hand, under wet conditions, almost all imprints presented a ring where the α-Al2O3 had been removed, driven by a corrosion-fatigue process. Exceptionally, for Cr-containing cemented carbides combined with Zr(C,N)/α-Al2O3 coating, no delamination of α-Al2O3 was observed after the test under wet conditions. This result suggests that the combination of fine-grained cemented carbides and coating systems with low coefficient of thermal expansion may be of advantage to resist degradation by cyclic contact fatigue. Furthermore, the response to fatigue by contact loads can be enhanced by tailoring/combining cemented carbides and CVD coating systems which present higher chemical stability, and both higher intrinsic plasticity and resistance to plastic deformation.
查看更多>>摘要：Cemented carbide tools are commonly used in both cutting and forging processes associated to zipper production. In production, the tools experience many millions of repeated contacts, hence they must be very durable to keep the wear at acceptable levels. Although the zipper elements in this investigation are made in a relatively soft CuZn alloy, the wear becomes significant and the tool life a production limiting factor. The wear process is to a large extent unknown. To increase the understanding, forging dies used for an increasing number of forgings in actual production, have been studied in detail. Initially the Co binder is preferentially worn off, and transferred CuZn partly fills the cavities. Interestingly, the repeating forging contacts lead to modification of the composition of the transferred material, which partly separates into Cu rich and Zn rich parts, where the Zn rich parts show a high presence of oxygen. During the life span of the tool, represented by the controlled use of forging tools to different percentages of their estimated life, the WC grains are gradually worn into faceted shapes. The most severely worn region of the forging dies develops an increasing surface roughness, which act to shape a corresponding pattern on the zipper elements.
查看更多>>摘要：The tribological properties of ionic liquids (ILs) have been widely investigated, and their excellent performance has been acknowledged by many researchers. However, their lubricity is closely linked to operating conditions. For wider applications, the complexity of their behavior must be understood. In this study, we compared the tribological properties of ILs at temperatures of 30 °C and 80 °C. Two ammonium ILs with different cation side-chain lengths, methyl-trioctylammonium [N1888] and tributylmethylammonium [N4441] and the same anion bis(trifluoromethylsulfonyl)imide [NTf2] were selected. Their tribological properties were investigated in the lubrication of three different friction pairs: bearing steel–bearing steel E 52100, bearing steel–stainless steel 304, and bearing steel–aluminum alloy 6082 T6. Tribotests were performed using a ball-on-plate reciprocating tribometer for 30 min at 4 N, 15 Hz, and a 1 mm stroke length. The worn surfaces were analyzed using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated diminished lubricity at higher test temperatures. The performance difference between the investigated temperatures depended on the friction pair, being almost negligible in bearing steel–bearing steel friction pairs and significantly different for bearing steel–aluminum friction pairs. The wear reduction ability was more sensitive to the test temperature than friction did. The investigated ILs were superior to the 5W–40 motor oil at both temperatures.
查看更多>>摘要：Rolling-sliding contact fatigue experiments were performed on through hardened (TH) 100Cr6 and surface induction hardened (SIH) C56E2 bearing steels to study the effect of heat treatment procedure and hardness difference on their wear and/or surface-initiated damage. The heat-treated microstructures included tempered martensite without the presence of retained austenite. It was found that initial stress distribution below the surface of TH specimens remains close to zero with respect to the depth, while, employing SIH resulted in relatively high compressive residual stresses. The wear damage of the specimens was characterized for negative ΔH (i.e., specimen's hardness minus counterpart's hardness) subjected to rolling-sliding contact in a twin-disc configuration operated under a mixed lubrication condition. According to the wear mechanisms and damages assessed, three regions were distinguished: i) mild wear and onset of micropitting, ii) transition region from mild to severe micro-pitting and iii) severe micro-pitting wear. Decreasing the ΔH resulted in a gradual increase in the wear rate of TH specimens, while, the increase in the wear rate of SIH specimens was delayed; with a same absolute hardness, TH specimen with a ΔH of ?84 HV already reached the third wear region, while a SIH specimen with a ΔH of ?150 HV still operates in the second region. Inspection of the affected subsurface unveiled the response of worn microstructures to the etchant and how the micro-cracks could possibly form within the wear affected zone. The results obtained were mainly explained based on the state of the residual stresses, possible contributions of the microstructural features, and wear behavior (material removal) of the specimen.
查看更多>>摘要：Cu–C pairs are the most widely used sliding current-carrying frictional pairs owing to their good conductivity and self-lubrication ability. This study investigated the variation in the current-carrying tribological properties of Cu–C pairs and the related wear mechanism at different relative humidities. The results can provide support for carbon brush design and safe service in humid air. In this study, the current-carrying coefficient of friction and contact resistance initially increased and then decreased, reaching maximum values at a relative humidity of 30%. With an increase in the humidity from 0% to 80%, formation of a tribofilm and reduced abrasive wear were observed by scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy results showed that the tribofilm on the Cu surface was a mixture of Cu, CuO, and C, and the humidity-assisted carbon transfer increased the atomic percentage of C from 60.96% to 81.13%. It was found that even for an existing tribofilm, the coefficient of friction increased immediately once the humidity support was lost. The results of this study showed that the mechanism for humidity-induced carbon lubrication was not oxidation. The lower humidity limit that could induce lubrication of the Cu–C pairs was approximately 60%.
NSTL
Elsevier