Intragranular precipitates in Incoloy alloy 909

Incoloy* alloy 909 is an Fe-Ni-Co based, age-hardenable, low-thermal-expansion superalloy. It has better combination of short-time tensile strength and elevated-temperature notch rupture strength. When aged at temperatures above 770 °C, the main intragranular precipitates formed are ε platelets that intersect with each other and form a Widmanstatten morphology. Anti-phase boundaries exist in ε platelets, which confirms that the ε phase has a highly ordered superlattice structure. Extensive selected-area diffraction analysis has determined that the ε phase has an hexagonal closed packed structure with lattice constants a = 0.458 nm and c = 1.202 nm. When observed by transmission electron microscopy, ε platelets exhibit less uniform contrast.