H S Ubhi 1 H Jiang 1 M Keeble 2 , and S Fritze 2 , Microstructural Characterisation of an Automotive Spark Plug using EBSD www.oxford-instruments.com Conclusions • Successful mechanical polishing was achieved for all the components and verified by optical metallography. • SEM/EBSD characterisation was similarly successful in accessing the processes and microstructures of the various components, e.g. coating of the terminal, inter-metallic formation at the interface between the copper and nickel in the central cored electrode, local melting as the erosion mechanism at the platinum electrodes. Introduction A pre-requisite for successful metallography is good sample preparation. This study illustrates the methodology for mechanically polishing an automotive spark plug, utilising both bright field and differential interference contrast optical microscopy to assess the surface condition, prior to SEM/EBSD characterisation. Methodology An automotive spark plug that had come out of service was sectioned and polished using the steps given in Table 1. The sample surfaces were examined using optical microscopy and the microstructures of the various components in the spark plug examined using the SEM/EBSD technique. The EBSD apparatus was attached to a FEGSEM and the EBSD data acquired using OI-HKL Nordlys detector combined with CHANNEL5 software. 1 Oxford Instruments plc, Halifax Road, High Wycombe, Bucks, HP12 3SE, UK. 2 Buehler UK, Step No. Surface Abrasive Lubricant Force Time Platen Speed Head Speed Relative Rotation 1 Apex DGD 75-15µm Water 6lbs until plane 250 60 Comp. 2 UltraPol 9µm MetaDi Supreme 6lbs 6 min 200 60 Comp. 3 Trident 3µm MetaDi Paste Metadi Fluid 7lbs 5 min 200 60 Comp. 4 Trident 1µm MetaDi Paste Metadi Fluid 7lbs 5 min 200 60 Comp. 5 ChemoMet 0.05µm Alumina / Colloidal Silica 7lbs 5 min 80 60 Contra 6 ChemoMet 5 parts Colloidal Silica+2parts 30%H 2 O 2 7lbs 6 min 80 60 Contra Table 1. Details of polishing steps Sectioning: Isomet 5000 Mounting: Simplimet 1000 Preparation: EcoMet-AutoMet Microscopy: Nikon MA-200 Al 2 O 3 Insulator - ceramic The fraction of amorphous phase is 6.6%. Mean size of alumina grains is 3.4µm with a maximum of 16.4µm. All Euler orientation map DIC image EBSP SEM BEI Centre Electrode tip Ni Pt PtNi IPF orientation map 20mm Local misorientation map 20mm FSD image 10mm 20mm SEM BEI DIC image IPF orientation map IPF orientation map IPF orientation map SEM BEI IPF orientation map SEM SEI Platinum tip, fine deformed structure, HAZ, local surface melting during service, weld metal – large grains inter-granular cracks. Pole figures Platinum electrode, large grains, local surface melting during service. Pt Phase map Pt Ni Side electrode EBSP 200mm 200mm IPF orientation map IPF orientation map SEM SEI SEM BEI Terminal: Nickel plating with outer oxide film formation Ferrite Ni All Euler orientation map EDS linescan Terminal Ni EBSP NiO EDS linescan Ferrite EBSP NiO EBSP DIC image Phase map Formation of intermetallic Cr 7 C 3 particles in the copper core at the Cu/Ni interface. Nickel Sheath - mean grain size of 10.9µm. Cr 7 C 3 IPF orientation map of Ni EDS Ni EDS Cr Phase map Ni Cu Cr 7 C 3 particles EDS Cu Cored central electrode 500mm EBSP DIC image DIC image Casing/side electrode joint: melting of casing, grain growth in electrode. Ni Steel Pole figures 500mm CSL boundary map Pole figures 500mm Deformation in thread root from thread roll forming process. IPF orientation map of steel 200mm DIC image DIC image DIC image IPF orientation map Local misorientation map IPF orientation map Steel Casing/side electrode joint Ni Centre electrode tip Side electrode Cored central electrode Casing threads Terminal Insulator - ceramic Casing/side electrode joint Spark Technical Poster_AW.indd 1 28/6/10 15:41:49