Introduction
Scanning Electron Microscopy (SEM)
Electron Dispersive X-Ray Analysis (EDX)
X-ray Fluorescence Spectroscopy (XRF)
X-ray Photoelectron Spectroscopy (XPS)
X-Ray Topography
Auger Electron Spectroscopy (AES)
Electron Energy Loss Spectroscopy (EELS)
Secondary Ion Mass Spectrometry (SIMS)
Rutherford Backscattering Spectrometry (RBS)
Chromatographic Analysis
Nuclear Reaction Analysis
Scanned Probe Microscopy
Non-destructive Evaluation (NDT) Techniques
Ultrasonic Techniques
X-ray Radiography
Thermography
Acoustic Emission
Eddy Currents
Surface and chemical characterisation techniques can provide basic and quantitative information relating to the process of degradation and failure of bonded joints. These techniques can provide important information on:
Chemical characterisation can be achieved using either spectroscopic or chromatographic techniques. Spectroscopic analysis provides detailed information about molecular structure, conformation, and physical-chemical characteristics of polymers, and chromatographic techniques enable quantitative compositional characterisation. This section provides a brief summary of surface and chemical analysis techniques that can be used to analyse and evaluate chemical, physical and mechanical changes due to the combined effect of mechanical loading and environmental exposure.
This is the most widely used of the surface analytical techniques. High resolution SEM has proved an invaluable tool for studying surface topography, oxide growth and failure analysis. The technique enables qualitative three-dimensional (3-D) imaging of surface features, however, it does not easily lend itself to quantitative surface roughness characterisation. This can be overcome by complementing SEM investigations with atomic force microscopy (AFM). In SEM, a highly focused scanning electron beam bombards the surface causing large numbers of secondary electrons to be generated, the intensity of which is governed by surface topography. The method is suitable for all materials, but non-conducting materials must be given a thin conductive coating (e.g. gold sputtered), which can alter or mask the true surface morphology. The resolution of topographical features is ~5 nanometres. SEM is often used to survey a surface before more specialised techniques are employed.
Untreated 6Al-4V-titanium alloy surface (magnification x 900)
Grit-blasted 6Al-4V-titanium alloy surface (magnification x 900)
6Al-4V-titanium alloy surface after grit blasting followed by CAE (magnification x 900)
EDX involves analysis of the elemental composition of a surface from X-rays emitted upon exposure to a primary beam of electrons. The X-rays emitted are characteristic of the atom from which they originated. Detection and analysis of characteristic X-ray lines of various elements can be obtained using an EDX system attached to an SEM. The maximum operational depth of EDX is typically 2 to 10 mm and the volume analysed can be as large as several cubic microns. The actual penetration depth depends on the type of material being analysed and the acceleration potential used in the SEM. The technique can be used generate elemental distribution maps of the area of interest, enabling both qualitative (boron to uranium) and quantitative (sodium to uranium) elemental analysis. The technique cannot provide information on chemical bonds, although it can provide information on element depletion and migration as a result of environmental exposure.
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