The effect of high temperature exposure on dendritic segregation in a conventionally cast Ni based superalloy

摘要

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 spectroscopy (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 1000°C. 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.