BS EN 843-6:2009 pdf free download – Advanced technical ceramics – Mechanical properties of monolithic ceramics at room temperature Part 6: Guidance for fractographic investigation.
6.6 Scanning electron microscope examination
6.6.1 If the investigation requires it, use the SEM to perform additional investigation of the fracture origin (3.1.4). Table 1 advises on the visibility of origins where SEM is needed.
6.6.2 If necessary, select regions of the specimen of suitable size for the available equipment. Using a diamond cutting wheel flushed with clean water, cut these regions from the specimen, clean them ultrasonically and dry them with compressed air. Mount them, preferably with mating halves adjacent, on an SEM specimen stub using a suitable adhesive. They should be cut and mounted in such a way as to allow viewing of both the fracture surface and the external surface. Remove dust and lint using compressed air. Mark the specimens appropriately to allow identification. If the material is not an electrical conductor, apply a thin conducting coating, e.g. carbon or metal such as gold.
NOTE I If EDX analysis is to be performed to identify an inclusion or compositional inhomogeneity, carbon is the preferred coating.
NOTE 2 To enhance the contrast developed the coating can with advantage be applied at an oblique angle to develop some shadowing effect.
NOTE 3 If operating at low SEM excitation voltage, a coating may not be necessary, but EDX analysis may not be effective.
6.6.3 Place the specimen in the SEM, and locate and examine the suspected fracture origin, initially at low magnification, and then at suitable higher magnifications, using secondary electron mode or back-scattered electron mode (enhances topography and atomic number contrast at the expense of resolution).
NOTE The contrast developed in the SEM is different to that observed optically, and some features, particularly the more subtle ones, can be lost.
6.6.4 If appropriate, prepare photographs of the fracture features, including (if relevant) the external surface adjacent to a surface or near surface failure, the mirror region, the radiating fracture lines and the origin. Identify the most likely origin.
NOTE It is recommended that a minimum of three photomicrographs are prepared at different magnifications appropriate to revealing the general fracture pattern, the mirror region, and the fracture origin.
6.6.5 Make appropriate notes of observations during the SEM examination.
6.7 Identification of fracture origin
Identify the nature of the fracture origin, and if possible describe it using the nomenclature in Clause 3 and Table 1. Where possible, define whether it is inherently a volume-distributed flaw (from the material microstructure) or a surface-distributed flaw (from any interaction between the specimen and its environment).
NOTE 1 Origins can sometimes be difficult to categorize uniquely, e.g. inclusions with associated microcracking, or pores associated with porous seams. If there is any doubt about the category full details should be entered in the report.
NOTE 2 In cases where there is no obvious microstructural or geometrical feature at the apparent origin, and this origin lies at the surface, it can be machining damage. If so, the origin can be one or more small arc-shaped flaws (cracks) from which fracture radiates. Machining damage is one of the most difficult types of fracture origin to define reliably.