doi:10.1016/j.engfailanal.2019.104214

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Contents lists available atScienceDirectEngineering Failure Analysisjournal homepage:www.elsevier.com/locate/engfailanalFailure of copper wires in a railway Motor Operation ContactNigel Brewitta,⁎, Spowage Andrewb, Caldwell Iana, Cook NeilaaIntertek, Elton Road, Derby, England, United KingdombQueen Mary University of London, Mile End Road, London E1, United KingdomARTICLE INFOKeywords:AmmoniaEnvironmentally assisted crackingFailure AnalysisABSTRACTMany engineering alloys can fail by environmentally assisted cracking (EAC). The risk of failureis dependent on the specific combination of material, the environment and the stress.Identification of the stresses (applied and residual) can be difficult because of the retrospectivenature of failure investigation and the commonly complex character of stresses in real en-gineering applications. A routine inspection of a Motor operation contact installed aside a railwayline in the British countryside found that the copper wire contact had failed. Standard failureinvestigation techniques combined with fractography were applied to identify an intergranularfailure mode. Experimental observations combined with a review of the relevant literature al-lowed the root cause to be assigned to environmental assisted cracking in the presence of gaseousammonia in the local environment.1. IntroductionCopper and its alloys are widely used in industries because of their desirable property profiles. Typical applications make use ofproperties such as good corrosion resistance, high electrical and thermal conductivity, mechanical workability and malleability[1].Copperfinds application particularly in electrical and electronic components such as of wire but also in other industries such asmarine and power as well as in specific products like heat exchangers and cooling towers[2,3]. Copper is a noble metal and has goodcorrosion resistance in the atmosphere.The durability of copper and its alloys is also acceptable in some chemical environments due to the formation of a protectivepassive (oxide)film or nonconductive layer of corrosion products on its surface. However, in some environments pitting corrosionmay occur in the presence of oxygen and some aggressive anions such as chloride and sulfate ions[4]. Accelerating factors includemoisture, temperature, and synergistic effects of chemical combinations and stress. Even low concentration of some chemicals canhave detrimental corrosive effects on copper and its alloys.A point machine,Fig. 1, located within 600 mm of the railway line ceased to operate, the fault being detected remotely andresulting is significant delays on the line. Close visual inspection found that the copper wires, attached to a Motor Operation Contact,had failed. The electrical components were housed in a non-sealed encasement,Fig. 3. This encasement would have provided pro-tection against sunlight and extremes of weather e.g. direct rain and snow as well as excess of dust and direct damage by projecteddebris. However, it was not atmospherically sealed so exchange of gases between the interior and exterior of the case would occur.The purpose of this investigation is to determine the failure mechanism of the copper wires to establish root cause.https://doi.org/10.1016/j.engfailanal.2019.104214Received 12 June 2019; Received in revised form 10 August 2019; Accepted 25 September 2019⁎Corresponding author.E-mail address:junigel@yahoo.com(N. Brewitt).Engineering Failure Analysis 108 (2020) 104214Available online 23 October 20191350-6307/ © 2019 Elsevier Ltd. All rights reserved.T

Nigel Brewitt

2. Experimental procedureInitial close visual inspection was carried out onsite. The failed component was identified and removed to the laboratory forfailure investigation. A photographic survey was carried out on the as-received component and also at various stages throughout theproject. Copper wire samples were removed for fractography and, after initial examination, cleaned using 5% Quadralene QIC/2instrument cleaner in water for 5 min in an ultrasonic bath. The contact clip was ground in two places to remove any coatings forchemical analysis of the underlying material. Fractography was carried out using an FEI environmental scanning electron microscopewith a 2 nm resolution capability. Chemical analysis was carried out using a Bruker Energy Dispersive spectrometer. Preparation formetallographic analysis was involved sectioning with a diamond saw, mounting the wire within conductive phenolic resin, grindingto 2500grit silicon carbide paper, polishing to 1μm diamond pastefinish,final polishing with colloidal silica suspension and etchingusing 10% alcoholic ferric chloride solution.Fig. 1.Motor Operation Contact showing fractured copper wires and connection point (Inset).Fig. 2.Position of contact within trackside assembly.Fig. 3.Trackside casing for contacts.N. Brewitt, et al.Engineering Failure Analysis 108 (2020) 1042142

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