Ni-Superalloy, as-extruded microstructure

The micrograph shows the three distinct phases of γ' present in polycrystalline superalloys. These are primary, secondary and tertiary γ', defined by their sizes (primary 0.5-1μm), (secondary 30-200nm), (tertiary 1-25nm) and their locations within the microstructure. Primary γ' segregates on the grain boundaries whereas the other forms are more uniformly distributed throughout the matrix. A grain boundary is clearly visible running from top right to bottom left. Due to the technique used, some γ' remains on the surface of the specimen and these 'echoes' can be seen in the replica - principally the primary γ' shapes on the grain boundary. There is also an increased density of tertiary γ' present alongside the grain boundary. View schematic diagram of γ' microstructur