Alpha Case Can Affect Corrosion Resistance
Alpha Case, Alloy Depletion, ASTM F136: The alpha case is the oxygen, nitrogen or carbon enriched alpha stabilized surface resulting from elevated temperature exposure. In certain Titanium alloys, the microstructure is strongly influenced by the processing history and heat treatment, and the alpha case can affect fatigue strength and corrosion resistance. (ASTM F136), in certain Titanium alloys there should not be any continuous alpha network at prior grain boundaries and there should not be any coarse, elongated alpha platelets.
Eutectic Melting Examination: Conducted primarily for the aerospace industry, this particular service can be offered under Boeing approval. Eutectic melting is a metallographic examination conducted on aluminum alloy materials and the phenomenon can occur whenever the eutectic melting temperature is exceeded. If the temperature during a thermal operation rises beyond the eutectic melting temperature, solid solution melting takes place. This drastically affects the mechanical properties of the aluminum and can quench cracking.
Phase Volume Fraction Determination: Many metallographic structures are dual or multi-phase. Examples are austenitic or duplex stainless steels which exhibit both austenite and Delta ferrite Phase. It is often important to quantitatively establish the phase balance as it can affect the mechanical and corrosion properties of the material. Two methods are mainly used, the preferred being manual point counting (ASTM E562). This method requires a square grid to be superimposed on a metallurgical microscope image at a suitable magnification and counts taken of underlying structures at the grid intersections. Depending on the expected volume fraction of a phase, a specific number of random counts are performed to give a good statistical population. Alternatively, volume fraction phase counts can be done automatically by image analysis.
