Eldar RahimovMichael WatsonAndreas HadjisoteriouMatthew Marshall...
19页
查看更多>>摘要：Abradable linings in aero engines have been an area of research interest over the past few decades as small reductions in clearances between stationary and rotating parts can lead to large increases in engine efficiency. The work performed in this article focuses on characterising the blade wear behaviour in contacts between Ti (6Al 4V) blades and AlSi-polyester abradables. This was done by performing three abrasion tests on the new test rig developed at the University of Sheffield. Tests have been performed on the AlSi-polyester abradables of the same nominal hardness over two incursion rates - 0.02μm/pass and 0.2 μm/pass and two blade tip speeds - 85 m/s and 170 m/s. The front-on stroboscopic imaging technique was used for these tests, which allowed capturing images of the entire blade front for a number of blade strikes during a test. It was found that at the incursion rate of 0.02μm/pass, both adhesions to the blade surface and blade wear were observed across the blade width. It was observed that adhesions were more likely to gradually wear off rather than fracture at 0.02μm/pass, and, fracture at 0.2 μm/pass. Tested surface profiles were obtained using an Alicona non-contact measurement system. This allowed the comparison of the blade profile results from the blade images to the surface of the respective tested abradable sample. It was concluded that adhesions that fractured could contribute to the localized gaps between the final blade and the final abradable surface where such adhesions have fractured close to the end of a test. Further testing areas have been identified such as the investigation into the effects of parameters such as incursion rate of a blade into an abradable, blade tip speed and abradable hardness on the results. The developed front-on imaging system also opened a possibility to investigate in-situ the rub performance of blades of varying tip geometry.
H. K. DanielsenF. Gutierrez GuzmanS. FaesterM. Shirani...
10页
查看更多>>摘要：White Etch Cracking (WEC) is a severe and unpredictable failure mode affecting bearings in various industrial sectors. In this work, accelerated WEC laboratory tests have been performed using FE8 type test rigs with ceramic rollers to test the WEC resistance of different bearing materials, materials quality and roughness. It is demonstrated that the test method can reliably and consistently provoke WEC in commercially available washers. Tests using washers with different roughness values did not show significant changes in the time to failure. Tests of through hardened bearing steel with a low content of inclusions resulted in a significantly longer time to failure compared to the baseline. Through hardened washers with a black oxide coating did not improve the WEC life as the coating was worn away during testing. Tests with two types of carbo-nitrided washers gave significantly longer time to failure, of which one type in particular showed high resistance towards WEC formation.
查看更多>>摘要：The polygonal wear of train wheels is common. It increases the wheel-rail interaction force drastically and adversely affects the safety and comfort of the train. The mechanism of the initiation and development of polygonal wear warrants further study. This study performed a high-speed rolling test based on the full-size wheel-rail roller test rig to reproduce the entire process of the generation and development of the polygonal wear on the tested wheelset of CL60 steel in the laboratory. The mechanism of the initiation and development of polygonal wear was analyzed using the test results, the bending resonance of wheelset was considered as an important cause of the polygonal wear in this paper. The basic condition for the polygonal wear formation and its high rate of development was verified. The evolution process of polygonal wear was studied in-depth, and the relationship between axle-box acceleration and polygonal wear was revealed. Effective countermeasures against the development of polygonal wear were proposed. Variable speed operation could mitigate the development of polygonal wear in this paper. The results obtained in this study may provide reference for the further study of the effective countermeasures against the development of polygonal wear.
查看更多>>摘要：Thick diamond films are synthesized on Si substrate by HFCVD method with different methane concentration (up to 21.9 vol%) in the gas mixture. The erosion resistance of the obtained coatings was investigated by the solid particle erosion of SiC. We show that, regardless of the microstructure, diamond coatings exhibit the same erosion mechanisms. Ring and radial cracks, as well as pin-holes and a local delamination of diamond film were detected for all synthesized films. We found that despite the high degree of initial roughness, the microcrystalline diamond coating showed the maximum erosion resistance at all stages of erosion experiments.
查看更多>>摘要：Wear debris entrapment or loading is a major problem with polycrystalline diamond (PCD) micro-grinding tools. This paper reports a step change in the performance of PCD micro-tool when square micro-pool array is fabricated on its secondary surface. The investigations on BK7 glass micro-slot grinding revealed that the proposed tool design with micro-pool array undoubtedly performs better in comparison to other tool, with reference to reduced cutting forces (by 30-48%), efficient debris disposal, improved surface finish (by 3 times) and tool utilization time (by 66%). Tool design and cutting force reduction are well justified and supported with analytical analysis of undeformed chip thickness and cutting forces.
查看更多>>摘要：Nanoscratch experiments under constant and ramp loading conditions are performed to investigate the delamination, and spallation characteristics of Zr-based thin-film metallic glass (Zr-based TFMG, Zr_(65)Cu_(15)Al_(10)Ni_(10)). TFMGs with different film thickness = 200, 500, 1000 nm are deposited over hard and soft substrates via DC magnetron sputtering process. Coefficient of friction (COF) is measured to be less about 0.03 regardless of scratch mode and maximum normal load. The critical load for thin film delamination and spallation reveals that the deformation and failure mechanism of Zr-based TFMG significantly change with film thickness and substrate type. The failure mechanism is characterized by observing the scratch grooves via optical and scanning electron microscopes (SEM). The adhesion energy between thin film and soft substrate is calculated based on Burnett and Rickerby model, and an increase in adhesion energy with interfacial layer thickness is reported.
查看更多>>摘要：Laser Shock Peening (LSP) has been widely employed as a post-processing surface treatment technique in improving fatigue resistance of various titanium alloy parts. However, most of the concerns on the LSP application are focused on the alteration in the subsurface layer, rather than the texture properties of the surface layer, which are crucial sensitive factors of the nucleation of fretting induced micro-crack. In this paper, the feasibility and ability of LSP treatment on the reconstruction of surface texture properties in four groups of sequentially milled hole surfaces were investigated. Two different impact routes were set to perform the LSP treatment. The produced surface texture properties, microstructure alteration, surface roughness, residual stress, as well as the fretting fatigue life and fretting behaviors were compared. The results showed that the LSP process could be regarded as a potential technique in constructing the surface texture to introduce beneficial resistance to fretting wear, by which the positive surface skewness value could be altered to negative, and the high surface kurtosis could be changed from leptokurtic to platykurtic or mesokurtic distribution. Moreover, the symmetrical strengthening method (SSM) in LSP treatment (LSPb route) tended to generate surface layer with a more negative skewness, better texture flow trend, numerous low angle grain boundaries (LAGBs), grains with high kernel average misorientation (KAM), and more refined grains, resulted in a lower crack growth rate and approximately doubling the fretting fatigue life. This work provides a method for reconstructing surface texture properties by LSP treatment to meet the performance requirement of components, as well as to expand the application field and ability of the LSP technique.
查看更多>>摘要：The subsurface white etching microstructure (WEM) was an important reason to cause the rolling contact fatigue (RCF) failure of wheel materials. The WEM formation mechanism in the subsurface layers of failed pearlite steel wheel was analyzed by using a scanning electron microscope, transmission electron microscope, and nanoindenter. The results showed that RCF cracks were mostly at the interface between the WEM and pearlite matrix. A large amount of the WEM was found in areas with no RCF cracks. This indicates that the WEM was formed prior to the RCF cracks. The WEM was comprised of nanostructured ferrite grains and residual cementite particles, and its hardness (approximately 920 HV) was about 3 times as high as that of the pearlite matrix. A soft area model for WEM formation is proposed based on the microstructural characteristics of two types of ferrite grains and the dissolution of cementite in pearlite resulting from continuous plastic deformation. During the wheel-rail contact, continuous plastic deformation in the subsurface under high contact stress conditions causes the successive refinement of the proeutectoid ferrite (PF) with low strength and ferrite grains in pearlite, the dissolution of cementite, and the improvement in the corrosion resistance, which cause the WEM to look white under an optical microscope. The WEM formation processes induced by alternating fatigue load were similar to that of surface nanocrystallization through surface mechanical attrition treatment. The great difference between the WEM and the pearlite matrix in the strength results in the crack propagating along their interface, therefore the nonuniform distribution of the WEM along both edges of RCF cracks was found commonly.
P. ThasleemDeepak KumarM. L. JoyBasil Kuriachen...
24页
查看更多>>摘要：Selective Laser Melting (SLM) is an innovative additive manufacturing technology that facilitates the design and manufacture of complex lightweight parts with improved mechanical properties. The current study investigates the impact of post-processing such as heat treatment and Electric Discharge Alloying (EDA) on the lubricated tribological behaviour of SLM Al-Si alloy at ambient and elevated temperatures in comparison with the tribological behaviour of conventionally cast Al-Si alloy. The lubricated sliding wear experiment conducted using a Pin on Disk (POD) tribometer with EN-31 alloyed steel as a counter body. The EDA treatment is highly appealing and enhanced the wear resistance of SLM Al-Si alloy by 14.07% and 24.07% at ambient and elevated temperatures, respectively. Moreover, the EDA treatment increased the wear resistance of cast Al-Si alloy by 28.82% and 46.28% at ambient and high temperatures, respectively, due to the development of a wear-resistant carbide (SiC) and oxide (Al_2O_3) rich modified layer on the surface. The T6 heat treatment in SLM Al-Si alloy caused deterioration in wear resistance by 10.74% and 36.73% at ambient and elevated temperature, respectively, due to the coarsening of the finer microstructure formed during SLM. In contrast, the T6 heat treatment in cast Al-Si alloy is highly effective in terms of wear resistance with an improvement of 13.26% and 13.64% at ambient and elevated temperature, respectively, due to the hardening effect caused by heat treatment. The prominent wear mechanism identified for all samples at both experimental conditions is severe abrasive wear due to plastic deformation.
查看更多>>摘要：The effect of strong oxidizer and operating temperature on the cavitation erosion (CE) resistance of pearlitic, bainitic, martensitic, and tempered martensitic microstructures made from a high carbon steel (HCS) using suitable heat treatment was studied. The mean erosion rates of the different microstructures (pearlitic, bainitic, martensitic, and tempered martensitic) of the HCS increased up to ～96, ～182, ～61, and ～117 times, respectively, in 3.5 wt% NaCl+ 0.1 N FeCl3 solution as compared to 3.5 wt% NaCl when the temperature remained constant at 25℃. This large increase in the mean erosion rates attributes to the addition of a strong FeCl3 oxidizer. Furthermore, the mean erosion rates of the above-mentioned microstructures of the HCS increased up to ～4.9, ～3.3, ～3.2, and ～2.7 times, respectively, when the solution was replaced after an hour without any temperature control.
NSTL
Elsevier