Solidification Characteristics of Advanced Nickel-Base Single Crystal Superalloys

Abstract

Twenty-two Ni-base superalloy compositions were investigated to assess the influence of the constituent elements on their solidification characteristics. Increasing the amount of Cr and Mo in high refractory single crystal alloys appears to reduce the extent of microsegregation of the dense refractory elements, W and Re. This is likely to be advantageous for maintaining single crystal solidification since alloys containing elevated levels of W and Re are prone to the formation of macroscopic grain defects during single crystal solidification. These findings suggest that elemental interactions between Cr, Mo, W and Re need to be considered when optimising alloys for high temperature creep properties. Ru additions also appear beneficial not only through stabilisation of the microstructure with respect to topological-close-packed (TCP) phase formation but also by reducing the degree to which Re partitions to the dendrite core. Linear regression has been applied to predict the solid-liquid partition coefficients for the major constituent elements and therefore provide an indication of the susceptibility of a given composition to freckle formation during directional solidification.