The Effect of High Temperature Exposure on Dendritic Segregation in a Conventionally Cast Ni Based Superalloy

Dendritic segregation in conventionally cast, commercially heat treated and exposed MarM002 turbine blades has been investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). During casting Cr, Co and W segregate to the dendrites and Hf, Ti and Ta segregate to the eutectics. As a result of the dissolution of γ' precipitates in the dendrites and coarsening of γ' precipitates in the eutectics this segregation aggravates during exposure at 1000oC. At this high exposure temperature homogenisation of dendritic segregation does not occur because it involves long diffusion distances and a low driving force compared with dissolution and coarsening of γ' precipitates.