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→13.4.1 Metallurgical Analysis
The main characteristic for the appraisal of contact materials for power engineering is the optical evaluation of their microstructure in a metallographic mount. This provides a picture of the internal structure of the materials. It allows detecting structural in-homogeneity, grain boundary enrichments, cracks, material separations, or defects in the brazing interface. The metallographic view is however limited to the one two-dimensional plain in which the mounting cut was made.
<xr id="fig:Microstructure of a powder metallurgical Ag CdO material"/> (Fig. 13.11 ) shows the microstructure of a Ag/CdO contact material after being affected by electrical arcing. In the lower part the starting material structure is visible. In the upper part the de-mixing of the composite material through the effects of the switching arc is clearly demonstrated. This “switching structure” shows in certain areas depletion of metal oxide which increases the probability of contact welding during subsequenbt make operations. Additional analysis by X-ray probing in a scanning electron microscope (SEM) allows the micro analysis of the elements present in the contact surface region.<figure id="fig:Microstructure of a powder metallurgical Ag CdO material">Fig[[File:Microstructure of a powder metallurgical Ag CdO material. 13.11:jpg|right|thumb|Microstructure of a powdermetallurgical Ag/CdO material afterbeing affected by intense electricalarcing]]arcing.</figure>
===13.4.2 Testing According to IEC/EN===