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Metallography
Metallographic sectioning for the quality control of materials and coatings as well as failure analysis, is an important technique that has been optimized by our laboratory so that it is often a crucial part of examination and investigation.​
Figure 1: Gray cast iron.
Graphite nodules bounded by ferrite grains ink a matrix of pearlite in spheroidal graphite iron. Etched with 2Wt.% Nital.
Figure 2: Fully Annealed Copper.
Ground and polished with diamond suspensions on a series of cloths, with a finish of 0.05 micron colloidal silica. An amonium sulfate solution was used to etch the surface to reveal the copper grains showing thermal twins.
Figure 3: Fully Annealed Tantalum.
Due to the ease of mechanical deformation, Tantalum has to be successively polished with an etching step in between. Because of the inherent corrosion resistance, a mixture of nitric and hydrofluoric acid has to be used.
Figure 4: Cross section through circumferential weld. Poor fit-up and lack of penetration in a TIG orbital weld in 316L stainless steel tube. The austenite grains have grown in the heat affected zone of the parent plate. Electrolitic etch with 10Wt.% oxalic acid.
Figure 5: Casting Defects.
Interdendritic shrinkage in the bore of a centrifugally cast stainless steel tube.
​Figure 6: Coating Defects. Weakness in ion vapor deposited coating. The individual nodules growth within the coating have left a path for corrosive gas diffusion to the substrate. The deliberate peening of the coating surface was not able to close the gaps between nodules.
Figure 7: Fractography.
Trans-granular, branching cracks through the annealed grains of austenitic 316L stainless steel are typical of chloride stress corrosion cracking at temperatures above 65°C. Electrolitic etch with 10Wt.% oxalic acid.
Figure 8
Failure of Gear Tooth due to Incorrect Heat Treatment. The tooth was hardened on the crown instead of on the flanks, which are the wearing surfaces. x5 magnification
Figure 9
Failure of Gear Tooth due to Incorrect Heat Treatment. Section through tooth flank showing heavy deformation of the normalized grains. x50 magnification
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