Browsing by Author "Lai, Q"
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- ItemCorrigendum to “Effects of preheating and carbon dilution on material characteristics of laser-cladded hypereutectoid rail steels” [Mater. Sci. Eng. A 712 (2018) 548–563](Elsevier, 2019-01-10) Lai, Q; Abrahams, R; Yan, W; Qiu, C; Mutton, PJ; Paradowska, AM; Fang, X; Soodi, M; Wu, XThe authors regret that the scale bar was missing from Figure 7. This has now been corrected. Fig. 7. Unaffected rail substrate and corresponding HAZ of a typical rail-transverse sections at (a) left gauge corner, (b) middle section, (c) right gauge corner and (d) representative of the longitudinal sections for (i) Group 1-1L, (ii) Group 1-2L, (iii) Group 2-1L & (iv) Group 2-2L. Martensitic morphology (M=martensite) with white etching colour were detected in (c) and (d) of the (i) Group 1-1L and (ii) Group 1-2L. Copyright © 2021 Elsevier B.V.
- ItemEffect of cladding direction on residual stress distribution in laser cladded rails(Zenodo, 2018-01-01) Roy, T; Paradowska, AM; Abrahams, R; Lai, Q; Law, M; Mutton, PJ; Soodi, M; Yan, WIn this investigation, a laser cladding process with a powder feeding was used to deposit stainless steel 410L (high strength, excellent resistance to abrasion and corrosion, and great laser compatibility) onto railhead (higher strength, heat treated hypereutectoid rail grade manufactured in accordance with the requirements of European standard EN 13674 Part 1 for R400HT grade), to investigate the development and controllability of process-induced residual stress in the cladding, heat-affected zone (HAZ) and substrate and to analyse their correlation with hardness profile during two different laser cladding directions (across and along the track). Residual stresses were analysed by neutron diffraction at OPAL reactor, ANSTO. Neutron diffraction was carried out on the samples in longitudinal (parallel to the rail), transverse (perpendicular to the rail) and normal (through thickness) directions with high spatial resolution through the thickness. Due to the thick rail and thin cladding, 4 mm thick reference samples were prepared from every specimen by Electric Discharge Machining (EDM). Metallography across the laser claded sample revealed four distinct zones: The clad zone, the dilution zone, HAZ and the substrate. Compressive residual stresses were found in the clad zone and tensile residual stress in the dilution zone and HAZ. Laser cladding in longitudinally cladding induced higher tensile stress in the HAZ, whereas transversely cladding rail showed lower tensile behavior. © Creative Commons Attribution 4.0 International License
- ItemEffect of deposition material and heat treatment on wear and rolling contact fatigue of laser cladded rails(Elsevier, 2018-10-15) Roy, T; Lai, Q; Abrahams, R; Mutton, PJ; Paradowska, AM; Soodi, M; Yan, WTo develop a laser cladding technique for repairing rail surface damages due to rolling contact, wear and rolling contact fatigue characteristics of a set of laser cladded rails were investigated using a roller-on-disc test machine. Three deposition materials 410L, SS420 and Stellite 6, were chosen to clad a premium hypereutectoid steel rail under two different heat treatment processes. In the first heat treatment, only preheating at 350 °C was conducted and in the second heat treatment, preheating at 350 °C, post-heating at 350 °C (1 h) then slow-cooling to room temperature was conducted. Preheating the substrate was insufficient to prevent martensite formation resulting from the rapid cooling rate, whereas post heat treatment was beneficial for refining the lamellar spacing and eliminating martensite formation in the clad layer and heat affected zone. Following the roller-on-disc tests, wear loss was calculated from wear track profiles using a laser optical profilometer. The level of surface degradation, surface cracking and spalling was investigated using an optical microscope. Experimental results revealed that SS420 cladding had the highest wear resistant behaviour but severe surface cracks and spalling were found in the worn area. Stellite 6 cladding showed similar wear resistance as the parent substrate rail and the best fatigue resistance behaviour among the three cladded rail samples. Based on this research, Stellite 6 is the most promising deposition material for repairing rails by laser cladding. © 2018 Elsevier B.V.
- ItemEffects of preheating and carbon dilution on material characteristics of laser-cladded hypereutectoid rail steels(Elsevier, 2018-01-17) Lai, Q; Abrahams, R; Yan, W; Qiu, C; Mutton, PJ; Paradowska, AM; Fang, X; Soodi, M; Wu, XThe impacts of preheating conditions and carbon dilution on the microstructural and mechanical properties of laser cladded rails using single and double cladding layers have been investigated for a hypereutectoid steel grades typically used under heavy haul conditions. The microstructures in the HAZ showed that formation of martensite, which has a detrimental effect on behaviour in wheel-rail contact, was successfully inhibited by increasing the length of the preheated region using a preheating temperature of 350 °C. Dilution of carbon from the hypereutectoid substrate was observed and its effect on the microstructures of the 410L ferritic stainless-steel deposits was investigated. The formation of ferrite in the 410L cladding layers was attributed to the very low carbon content, and no carbide formation was observed on boundaries of the ferritic grains. The thickness of dilution band was determined to be approximately equal to the thickness of the first cladding layer. Texture measurement obtained by EBSD showed a random trend owing to the formation of martensite in diluted bands. Strong solidification fibre texture was developed for double deposition, particularly in the second deposit. Mechanical characterization of the 410L deposits undertaken in terms of Vickers microhardness, shear and tensile yield strengths, and ultimate tensile and shear strengths were correlated with the observed microstructural morphologies. © 2017 Elsevier B.V.
- ItemEvaluation of the mechanical properties of laser cladded hypereutectoid steel rails(Elsevier B. V., 2019-08-15) Roy, T; Abrahams, R; Paradowska, AM; Lai, Q; Mutton, PR; Soodi, M; Fasuhi, P; Yan, WLocal material properties of the cladding layer, heat affected zone and substrate of laser cladded hypereutectoid steel rails were evaluated by uniaxial tensile tests on miniature specimens. Three laser cladding materials, i.e. 410 L, SS420 and Stellite 6, and two different heat treatment conditions were considered. To examine any possible anisotropic behaviour, specimens machined along the longitudinal and transverse laser cladding directions were tested. All the cladding layers showed similar or higher yield and ultimate tensile strengths, but lower elongation than the non-clad rail. Application of post-heat treatment significantly improved the elongation of all the cladding layer specimens. Elongation increments of 70%, 192% and 90% were respectively obtained from the 410 L, SS420 and Stellite 6 post-heat treated cladding layers. The post-heat treatment also marginally increased the yield and ultimate tensile strengths in this region. The improvement in tensile properties was associated with a more favourable microstructure, which resulted in a more dimpled morphology as depicted in the SEM images of the fractographic analysis of the tested specimens. While other properties are similar, both cladding layer and HAZ specimens showed significant different elongation values between the longitudinal and transverse directions in some cases, which indicates certain anisotropy in those materials’ ductility. © 2019 Elsevier B.V.
- ItemFinite element analysis of thermal cycle in laser cladding for railway repair(Engineers Australia, 2017-01-01) Lai, Q; Abrahams, R; Yan, W; Mutton, PJ; Qiu, C; Paradowska, AM; Soodi, M; Roy, TMaterial degradation in the forms of wear and rolling contact fatigue is one of main hindrances in the development of today's expeditious heavy-haul railway systems. Laser cladding is proposed as a promising repair technique for damaged rail tracks so as to mitigate the material degradation rates and prolong the component service life. This paper reports the influence of laser cladding directions on thermal cycle and the corresponding mircostructures and service performance of laser cladded premium hypereutectoid rails. For two separate cladding directions, thermal information of pre-, during and post-laser treatment on three dimensional 68 kg rail models was simulated via ANSYS platform. Furthermore, microstructural characteristics of the actual rails under the analogous processing conditions were assessed via optical microscopy. Potential mechanical and tribological properties were characterized by Vickers indentation. The unified correlations between the measured properties and observed microstructural features were acquired. The reasons for the formation of martensite renowned for great cracking tendency at certain regions in HAZ were unveiled, thus future prevention of forming martensite can be achieved.
- ItemInfluences of depositing materials, processing parameters and heating conditions on material characteristics of laser-cladded hypereutectoid rails(Elsevier, 2019-01-01) Lai, Q; Abrahams, R; Yan, W; Qiu, C; Mutton, PJ; Paradowska, AM; Soodi, M; Wu, XThe effects of different cladding materials, processing parameters and heating regimes on the underlying microstructural features and mechanical properties of laser-cladded premium rails were investigated by using a hypereutectoid rail grade as a substrate, which is extensively used in heavy-haul rail systems. Cladding materials of 410L, 420SS, Stellite 6 and Stellite 21 with single and double depositions were considered for the comparative study of different cladding materials and processing parameters. To ensure the constant thickness of the claddings for comparison purposes, transverse speed and powder feed rate were modified concurrently in the ranges of 1000–1200 mm/min and 3–4 RPM, respectively. Two heating conditions, i.e. preheating only (HTA) and a combination (HTB) of preheating and post weld heat treatment (PWHT) were applied after the preferable parameters for each cladding material were obtained. The most suitable cladding material for rail-wheel contact was established by assessing all crucial aspects, i.e. surface defects, hardness, microstructural and mechanical properties. Process parameters for each considered cladding material were determined to achieve no surface defects. For cladding layers, application of HTA was not able to significantly modify the microstructures of the deposits, whereas HTB was observed to cause severe cracks in Co-base alloys, i.e. Stellite 6 and Stellite 21. In the heat affected zones (HAZs), irrespective of the cladding materials, the formation of untempered martensite was not avoided by the application of preheating at 350 °C. Consequentially, cracking in the HAZ was observed. An uncracked and desirable microstructure in the HAZs was established using HTB, regardless of the depositing materials. The addition of a second layer did not change the thickness of the HAZs but refined the HAZ’s microstructures. Shear punch testing (SPT) and Vickers hardness testing were utilized to characterize mechanical properties for the considered cladding materials and good correlations with the obtained microstructural morphologies were shown. © 2018 Elsevier B.V.
- ItemInvestigation of a novel functionally graded material for the repair of premium hypereutectoid rails using laser cladding technology(Elsevier, 2017-12-01) Lai, Q; Abrahams, R; Yan, W; Qiu, C; Mutton, PJ; Paradowska, AM; Soodi, MIn this study, the effects of cladding direction, preheating and post heat treatment on microstructural and mechanical properties of laser cladded rail repairs are presented. Laser cladding of a premium hypereutectoid rails grade with 410L stainless steel powder were conducted using a fibre laser gun with a powder feeder. Two different cladding directions and different heat treatment regimes were investigated. An excellent microstructural consistency was established across the railhead and its heat affected zone (HAZ) by changing cladding direction and using a heat treatment consisting of pre-heating and post-heating. The microstructure of the cladding layer and HAZ were characterized by optical microscopy and SEM. Phase identification and distribution were investigated by using XRD, EDS, and EBSD. Indications of the mechanical and tribological performance of the cladding layer in wheel-rail contact were obtained via shear punch tests and Vickers indentation, which demonstrated great correlation with the obtained microstructure. © 2017 Published by Elsevier Ltd.
- ItemLaser cladding for railway repair: influence of depositing materials and heat treatment on microstructural characteristics(American Society of Civil Engineers (ASCE), 2017) Lai, Q; Abrahams, R; Mutton, PJ; Qiu, C; Paradowska, AM; Soodi, M; Roy, T; Yan, WThe contact between train wheels and rail tracks is known to induce material degradation in the form of wear, and rolling contact fatigue in the railhead. Laser cladding, a state of the art surface engineering technique, is a promising solution to repair damaged railheads so as to alleviate the rates of degradation and extend the component longevity. In this paper, effects of cladding material and heat treatment on microstructures of laser treated rails is presented. Laser cladding of premium hypereutectoid rail, four different depositing materials, and different heat treatments were investigated. For the preheating length of 400 mm, equal to the cladding length, the formation of martensite in heat affected zone (HAZ) was not hindered by the application of preheating to 350 °C on the rail-longitudinally deposited railhead of the four materials. Consequentially, cracking in the clad and HAZ was expected. An uncracked microstructure with excellent microstructural consistency across the entire rail-longitudinally deposited railhead and its HAZ was established using a heat treatment combination consisting of pre-heating, postheating, and slow cooling, regardless of the depositing materials. © 2018 American Society of Civil Engineers
- ItemMaterial characteristics of laser-cladded hypereutectoid rail steels(Railway Technical Society of Australasia (RTSA); Technical Society of Engineers Australia. , 2018-01-01) Lai, Q; Roy, T; Abrahams, R; Yan, W; Paradowska, AM; Qiu, C; Mutton, PJ; Soodi, MThe impact of preheating conditions and carbon dilution on the microstructural and mechanical properties of laser cladded rails at various number of deposition layers has been investigated for hypereutectoid steel grades typically used under heavy hall conditions. The microstructures in the HAZ showed that formation of martensite, which has a detrimental effect on behaviour in wheel-rail contact, was successfully inhibited by increasing the length of the preheated region using a preheating temperature of 350C. Dilution of carbon from the hypereutectoid substrate was observed and its effect on the microstructures on the 410L ferritic stainless-steel deposits was investigated. The formation of the ferrite in the 410L cladding layers was attributed to the very low carbon content, and no carbide formation was observed on boundaries of the ferritic grains. The thickness of the dilution band was determined to be approximately equal to the thickness of the first cladding layer. Mechanical charaterization of the 410L deposits undertaken in terms of Vickers microhardness was correlated with the observed microstructural morphologies. © 2021 Informit
- ItemTribological behaviour of laser cladded rail under rolling contact test(American Society of Civil Engineers (ASCE), 2017) Roy, T; Abrahams, R; Lai, Q; Mutton, PJ; Soodi, M; Paradowska, AM; Yan, WWRolling contact fatigue (RCF), a pervasive and insidious problem on all types of railway systems, dominates the cause of maintenance and replacement on heavy-haul rail lines. It also plays a significant role in economic and safety challenge for commuter and metro lines. Intensive research around the world has been taken to improve RCF by introducing different surface modification techniques. Laser cladding has attracted attention because of its advanced and more efficient repairing technique. In this present investigation, influence of laser cladding on wear and RCF of a premium hypereutectoid rail steel, currently used in Australian heavy haul railways, has been studied under a roller-on-disc test rig in laboratory conditions. Rolling test was carried out using a roller made of heat treated harden steel with laser cladded and un-cladded rail steel discs. Micro-hardness of the roller was 820-850 HV5 to minimize plastic deformation and wear of the roller. Considering the real scenario of rail-wheel contacts, tests were run under partial sliding and rolling motion. The maximum contact pressure was similar to that experienced in rail due to rail-wheel contact. Wear resistance of laser cladded specimen was found to be significantly improved compared to non-cladded rail steel. © 1996–2021, American Society of Civil Engineers