Cooling rate dependent morphology of the γ' precipitates in nickel-base superalloy Udimet 500

摘要

The morphology of the γ' precipitates during continues cooling of a nickel-base superalloy, Udimet 500, was studied using scanning electron microscopy and X-ray diffraction technique. The samples were full solutioned at 1200°C and then were cooled to ambient temperature under different cooling rates, 15, 1, 0.2, 0.05°C /min and air cooling. The unconstrained γ-γ' misfit values for each sample were calculated using the electrolytic extracted γ' precipitates. According to the results, by decreasing the cooling rate, not only the size, volume fraction and interparticle spaces of the γ-γ' precipitates were increased, but also depending on the γ-γ' lattice misfits the corresponding γ' morphology was changed from spherical to cubic, then flower-like and finally dendritic shape. The observations are discussed in view of the compositional changes of γ/γ' phases and elastic strain considerations of their interfaces which will be described in detail in the article.