Cast microstructure of Inconel 713C and its dependence on solidification variables

Abstract

The dependence of cast microstructure of Inconel 713C on solidification variables was investigated over a wide range of local cooling rates, ∈, and thermal gradients in the liquid at the solid-liquid interface,G. The shape of MC carbide particles was found to depend greatly on: 1) theG/R ratio at the solid-liquid interface, whereR is growth rate, through the effect of this ratio on the solid phase,γ _γ , growth morphology. Under planar front growth conditions the carbide particles were octahedral, under cellular growth conditions they were plate-like, elongated along the cellular growth direction, and under dendritic growth conditions they were irregularly shaped; 2) the local cooling rate, ∈, when γ was dendritic, with a transition from octahedral to dendritic with increasing ∈. The size of MC carbide particles was found to be controlled by coarsening and to become finer with increasing ∈. In this alloy the composition of the MC carbide was established as (Nb_0.63Ti_0.31Mo_0.06) C and was practically independent of local cooling rate. Other observations were that the precipitation of γ′ and the formation of nonequilibrium eutectics, such as MC-γ, γ-γ′ or MC-γ-γ′ were suppressed at splat-cooling rates. Also, microsegregation of all alloying elements with the exception of aluminum was normal, with concentration increasing from the dendrite center-line to the dendrite arm boundary. Aluminum behaved in the opposite manner. Within the cooling rate range used herein, this variable had only a slight effect on microsegregation.