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With the rapid development of railway towards being high speed and having heavy load capacity, the wheel–rail wear and rolling contact fatigue in the curve section with a small radius of freight have become the key problems in urban railways, which need to be solved urgently. The aims of this study were to compare the wear resistance with three different lubricating conditions on wheel–rail wear based on the wheel–rail rolling contact simulation tests. The wear loss, microhardness, and microstructure of the contacted surface of the rail were detected systematically. The results showed that the wear rates of rail were reduced by 71% for grease lubrication and 55% for solid lubrication, compared to those without lubrication. At the same time, the thickness of plastic deformation layer of rail samples were about 167 μm for the dry state, 138 μm for the solid lubrication state, and 128 μm for the oil lubrication state, respectively. It indicates that the thickness of the plastic deformation layer was significantly reduced under both grease and/or solid lubricating conditions. In addition, the microstructure of the deformation layer with two kinds of lubricated states was coarser and denser than that without lubricants. The average grain size of the deformation layer was approximately 0.22 μm under dry conditions and 0.32 μm under lubricated conditions. It also indicated that the changes in lubricants did not have a significant effect on the average grain size of the deformation layer. The results of the present study could provide theoretical reference for the development and design of lubricants used as rail materials. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) has been considered as a promising method for repairing rails and extending their service life. In this work, the wear rates of twin-disc specimens produced through laser additive manufacturing against ER7 material are studied applying creepages from 0.4 % to 2.6 %. The approved E11018-G electrode material is atomised and fully cladded into twin-disc rail specimens by Laser Powder Directed Energy Deposition. After the weight loss tests at 1400 MPa, experimental results are fitted with the theoretical adhesion curve modifying FASTSIM coefficients. This adhesion curve is employed to numerically calculate the slip contact area of each test. A non-linear correlation has been found and defined between wear and the slip area including the non-linear zone. This relationship is identified for tribochemical wear for low creepages and delaminative wear for middle and high creepages by surface and metallographic characterisation. The obtained results allow to predict the wear of the additively manufactured E11018-G repair material under wheel-rail contact conditions when the slip area is known. • Investigation of wear rates of powder grade E11018-G material cladded by Laser Powder Directed Energy Deposition, a material traditionally used to repair R260 rails. • The E11018-G material was deposited onto C45 steel, with a similar microstructure to R260, in the specimens employed for weight loss and adhesion curve tests. • In-depth analysis of the surface and microstructure after wear testing, identifying oxidative wear and delaminative wear as key mechanisms. • A fitted polynomial is obtained to predict wear rates under full slip conditions for known maximum normal pressure and friction coefficient at saturation. [ABSTRACT FROM AUTHOR]

Wettability and stress concentration are the main challenges affecting the engineering application of copper/alumina dissimilar joints. In this paper, continuous drive friction welding of copper to alumina was conducted using 2.5 mm thick AA1100 aluminum as interlayer. The effects of friction pressure and friction time on the tensile strength of joints were evaluated, and the interface microstructure evolution and fracture morphologies were also analyzed. Obvious mutual diffusion occurred at the alumina/aluminum and aluminum/copper interfaces, enhancing wettability and proving metallurgical bonding. Microcracks formed in alumina base due to thermo-mechanical coupling effect in welding. As increasing friction pressure and friction time, the tensile strength increased till reaching a peak value of 35 MPa, and then decreased. The optimized parameters were determined as friction pressure of 12 MPa and friction time of 12 s. All samples failed at the aluminum/alumina interface, leaving a pit structure on alumina base. The application of pure aluminum interlayer is essential to obtain sound copper/alumina joints by diminishing stress concentration and wetting alumina, and the optimized residual aluminum layer is about 0.47 mm thick. The friction interface transferred from alumina/aluminum to inner plasticized aluminum layer, and then moved to aluminum/copper till the welding process finished. [ABSTRACT FROM AUTHOR]

Most existing wheel/rail hardness matching studies have been carried out using pearlite steels with different hardnesses; no relevant wheel–rail hardness matching research has been carried out for other microstructure types such as bainite and other tempered materials. In this paper, a CL60 wheel (pearlite) was quenched and tempered to obtain wheel materials with a certain hardness gradient, and matching tests between different wheel materials and a quenched U75V rail were carried out to explore the influence of wheel microstructures on wheel–rail damage. The results showed that with increasing tempering temperature, the wheel microstructure changes from tempered troostite to tempered sorbite, with ferrite changing from a needle shape to a multilateral shape; additionally, the cementite particles grow obviously larger, resulting in a gradual decrease in wheel hardness. With the increase in the wheel/rail hardness ratio, the wear rate of the wheel and wheel–rail system first increases and then decreases; the wear rate of tempered sorbite is the highest. Wear surface analyses indicate that typical peeling appears on the wear surfaces of the CL60 wheel as well as the coupled rail. Tempered sorbite shows slight peeling; however, severe peeling and delimitation occur on the wear surface of its coupled rail. Moreover, severe peeling and serious material delamination are present on the wear surface of tempered troostite, and typical peeling appears on its coupled rail surfaces. The fatigue crack initiation and propagation behaviors of wheel and rail materials are closely related to their microstructures. The cracks in pearlite always initiate on the surface and propagate along the ferrite line. Short and shallow fatigue cracks appear on the tempered sorbite with a high wear rate, and the cracks in the tempered troostite easily expand into the centre of the samples, indicating poor rolling contact fatigue (RCF) resistance. Therefore, the pearlite structure shows better comprehensive mechanical properties for wheel service; moreover, more attention should be given to wheel microstructure when conducting research on wheel–rail matching. • The CL60 wheel were heat treated and wheel materials with a certain hardness gradient were obtained. • Matching tests between quenched U75V rail and different wheels were carried out. • Wear and rolling contact fatigue behaviours were proposed and studied. • Ratcheting behaviours and propagating mechanism of RCF cracks were analyzed and revealed. [ABSTRACT FROM AUTHOR]

Systematic experimental investigations were conducted to study the damage behavior of rail steels with eutectoid and hypereutectoid microstructure under different axle load and curve radius conditions. The wear resistance and resulting failure mechanism, as well as subsurface crack development were evaluated by wheel/rail rolling contact test rig, which can realize a broad range of working conditions from mild condition to harsh condition. Results demonstrate that the wear resistance and rolling contact fatigue (RCF) damage depend on not only the working conditions employed, but also the microstructures. With the increase of axle load and reduction of curve radius, the wear rate increases for both rail steels. Damage mechanisms for the two rail materials are mainly surface fatigue cracks and delamination, which become much serious from the mild condition to harsh condition. The hypereutectoid rail possesses a better wear resistance than eutectoid rail in general. Wear regime map suggests that the hypereutectoid rail did not have a catastrophic wear region, but can be observed in eutectoid rail. The subsurface analysis shows that the working condition has a significant impact on surface crack development depending on specific microstructure types. The hypereutectoid rail is more suitable for harsh working conditions than eutectoid rail. • Wear and damage of two rail materials were investigated under harsh conditions. • High axle load and small curve radius play great effects on damage of rail materials. • Rail steel microstructure affects the fatigue cracks development. • Hypereutectoid rail did not have catastrophic wear region as observed in eutectoid rail. • Hypereutectoid rail is more suitable for harsh conditions than eutectoid rail. [ABSTRACT FROM AUTHOR]

Abstract: Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track. [Copyright &y& Elsevier]

Abstract: Serious problems have been observed in railroad systems as a consequence of uncontrolled wear, which is considered a key factor regarding performance losses and maintenance costs. One alternative to face the demanding requirements of the newest systems is the development of materials with more resistant and durable microstructures. In order to study the behavior of AISI 15B30 (bainitic) and AISI 1070 (pearlitic) steels, a disc-on-disc tribometer was used to test them under properly controlled load and relative slip conditions. The steels were conveniently heat treated to obtain hardness values similar to those of actual wheels and rails in commercial railroad systems, i.e. 320HV for the wheels and 370HV for the rails, and only pairs of discs made of the same material were tested each time. The results indicated that the average wear rates were similar for all the pairs and slip ratios tested. Under pure rolling, both AISI 1070 and AISI 15B30 showed larger deformed subsurface layers and more significant work hardening when compared to rolling–sliding conditions, which was related to the magnitude of stresses beneath surface for each condition. [Copyright &y& Elsevier]

Abstract: Driven by a requirement for increased performance and cost-effectiveness, the basic pearlitic microstructures of rail steels are being progressively refined and novel microstructures are being developed. With such progress, increased attention must be paid to potential ‘weak spots’ in the microstructure such as non-metallic inclusions. For the past few decades, rail steels have become progressively cleaner with regard to harmful brittle inclusions, however the effect of rolling–sliding contact forces on nominally benign, ductile inclusions requires further consideration. This work examines the characteristics of ductile, Mn-based inclusions in used rail and rail test discs. Where the structure near-surface has been subject to a high component of transverse creepage, ductile, axially aligned inclusion ‘stringers’ become strain-flattened to form planes of weakness along which micro-cracks initiate and propagate, thus facilitating wear and rolling contact fatigue (RCF) cracking. The progression of shape change of these ductile inclusions approaching the contact surface has been examined by optical and electron microscopy including focussed ion beam (FIB) analysis. As-manufactured ductile inclusions shapes and distributions have also been surveyed with respect to the (geographical) source of the rail steel. Comparative data for these different steel sources are given. [ABSTRACT FROM AUTHOR]

Abstract: Hadfield steel is well known for its high work hardening capacity and wear resistance. The alloy X120Mn12 is specifically used in railroad castings such as frogs and crossings in west European countries such as France. The influence of various contact parameters on the mechanical behaviour of this alloy was investigated by rolling contact tests. The results are described and discussed using micro-hardness measurements, optical and scanning electronic microscopy and EBSD analyses. [ABSTRACT FROM AUTHOR]

Abstract: The primary aim of this investigation is to examine the influence of pre-strain on wear behaviour of plain carbon steels. Experimental work comprises of detailed measurement of wear rate, microstructural characteristics, hardness, tensile properties of unstrained and pre-strained specimens, and SEM examinations of the worn-out surfaces and subsurfaces of five hypo-eutectoid and one nearly eutectoid steel. The results assist to infer that: (1) wear rate of pre-strained specimens increases with increasing pre-strain up to a critical value of the latter beyond which it drops with further increase in pre-strain, (2) wear behaviour of all the investigated hypo-eutectoid steels exhibits a critical pre-strain as 0.7±0.05, normalized with respect to uniform strain, (3) simultaneous increase of wear rate and hardness up to the critical value of pre-strain is contrary to Archard''s law; this has been explained by the ease of nucleation of voids/micro-cracks and their subsequent propagation during sliding wear of pre-strained specimens, and (4) wear rate is found to be considerably dependent on the microstructural constituents of the steels beyond the critical value of pre-strain. [Copyright &y& Elsevier]

Plasma selective quenching is a technology which can significantly improve the wear resistance of rail material. However, there are few studies on damage characteristics of rail materials with plasma selective quenching (PSQ). In this study, the influence of PSQ on wheel-rail wear and damage characteristics was studied. The research results show that PSQ has a great influence on damage characteristics of rail materials; PSQ can significantly reduce rail wear; The damage characters of quenched specimens could be divided into three stages: quenched zone wear, quenched zone wear and spall pits, substrate wear. •The influence of the plasma selective quenching on wheel-rail wear and RCF damage was studied. •An electron microscope was used to observe the damage of the wheel/rail surface. •Plasma selective quenching has a great influence on RCF damage of wheel and rail. •An excessive proportion of the quenched area of rail leads to increased wheel wear. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni-Cr-Fe (N), 17-4PH (MP) and 18Ni300 (MS) coating are deposited on rail by LIHC. • The microstructure and hardness of N coating show little change in different layer. • The grain size and precipitates' content of MP and MS coating vary in different layer. • Wear rate, PD depth and surface damage of rail with MP and MS coating are all reduced. • LIHC deposited MS coating shows the best competitiveness in the rail repairing. In this paper, Ni-Cr-Fe, 17-4PH and 18Ni300 alloy coating were deposited on the rail surface by laser-induction hybrid cladding (LIHC), respectively. The microstructure, microhardness of different coatings, and their influences on the wear properties and contact fatigue behaviors of rails were studied systematically. Results indicate that the as-deposited Ni-Cr-Fe coating is constituted of the dendrite structure, and the as-deposited 17-4PH and 18Ni300 coating mainly consist of the lath martensite structure. The microstructure and microhardness of Ni-Cr-Fe coating are little influenced by the in-situ thermal cycling in LIHC process, whereas the grain size and precipitates' content in 17-4PH and 18Ni300 coating are affected significantly, making the microhardness therein increased along the depth direction. Compared with the untreated rail, the wear rate and plastic deformation (PD) depth of rails with 17-4PH and 18Ni300 coating are both decreased significantly, while the contact surface damage is alleviated simultaneously. Especially for that with 18Ni300 coating, the decreased proportions are as high as 40.2% (mass wear rate), 60.1–81.2% (dimensional wear rate) and 78.7% (plastic deformation depth), respectively. By contrast, the wear rate of rail with Ni-Cr-Fe coating is increased conversely than that of the untreated rail although its microhardness is 32% higher. Therefore, the LIHC deposited 18Ni300 coating is a competitive choice for repairing the rail in engineering. [ABSTRACT FROM AUTHOR]

As the industry of railway transportation is thriving, much more attention has been paid to the properties of wheel/rail steel materials. Although conventional wheel/rail steel materials have proved their competence so far, it is necessary to think ahead and develop new wheel/rail steel materials in order to meet new challenges raised by railway transportation in the future. Since bainitic steel is the first choice for the new wheel/rail steel material, it is especially important to fundamentally investigate its wear property. Through the sliding wear experiment on AB1 bainitic rail steel, the microstructural evolution of bainitic steel during the wear process and the factors that affected its wear property were probed into in this paper. Under sliding wear, it was discovered that ploughing wear, adhesion wear and flake-like peeling were the primary morphological characteristics of AB1 bainitic rail on the worn surface, and the flakes generated by peeling were relatively thin; WELs appeared on the worn surface of AB1 bainitic rail steel, with the thickness of less than 20μm. The main microstructure inside the WELs contained nanoscale bainitic ferrite grains and martensite grains. Under the impact of stress, the surface microstructure of AB1 bainitic rail steel underwent the following changes: the direction of bainitic ferrite laths gradually became perpendicular to that of the stress, and with the increase of the deformation strain and strain rate, bainitic ferrite laths were segmented into numerous short bar-shaped subgrains and even into nanoscale equiaxed grains with random orientations; residual austenite, no longer stable, underwent martensite transformation, and after the formation of martensite, under the influence of pressure stress, martensite lath grains were multidirectionally segmented into pieces that formed nanoscale martensite grains. Residual austenite inside the microstructure of AB1 bainitic rail steel, the thickness of bainitic ferrite laths and the WELs formed during the wear process would all affect the wear property of bainitic steel. • During sliding wear, WELs would form on the worn surface of AB1 bainitic steel, with the thickness of less than 20μm. • The microstructure evolution law of AB1 bainitic steel during sliding wear was presented. • The factors that affected the wear property of bainitic steel were discussed. [ABSTRACT FROM AUTHOR]

To investigate the relationship between surface microstructure and wear mechanism in D2/U71Mn wheel-rail material under different contact stress conditions, rolling wear tests using a GPM-40 wear machine to simulate the wheel-rail operation was performed. After wear tests, an optical microscope (OM), scanning electron microscope (SEM) and micro-hardness testers were used to characterize the microstructure and fatigue wear cracks. The results show that the thickness of the plastic deformation layer and surface hardness is increased with the increase of contact stress. Under high contact stress condition (1200 MPa), the severe plastic deformation layer led to the formation of fatigue wear of wheel-rail samples. Under a contact stress of 700 MPa, the wear mechanism of samples is adhesive wear and wear rate is low. With the increase of contact stress, the fatigue cracks are gradually severe. Under a contact stress of 1200 MPa, the wear mechanism of samples becomes fatigue wear and the fatigue wear cracks cause the increase of wear rate. The fatigue wear can accelerate the wear failure of wheel-rail samples. The fatigue wear cracks of wheel samples are severer than that of rail samples due to both the rate of plastic strain and the content of proeutectoid ferrite. [ABSTRACT FROM AUTHOR]