Dendrite evolution and quantitative characterization of γ′ precipitates in a powder metallurgy Ni-based superalloy by different cooling rates

Abstract

The effect of cooling rate after super-solvus heat treatment on the morphological evolution of γ′ precipitates in an advanced powder metallurgy Ni-based superalloy, FGH4113A, was systematically investigated. The quantitative relationship between the cooling rate and γ′ precipitates was elucidated in detail. The results showed that at cooling rates of 200 °C/min and 600 °C/min, the primary branch of dendritic γ′ grew along the< 111 > direction, whereas the secondary branch grew along the< 100 > and {111} directions. In addition to the interfacial and elastic strain energies, the width of the γ′ channel significantly impacted the evolution of the secondary dendritic orientation of γ′. As the cooling rate decreased, the size and volume fraction of the γ′ precipitates increased, whereas the nucleation density of the γ′ precipitates decreased. A strong power-law relationship between the characterization of the γ′ precipitates (such as volume fraction, nucleation density, particle size) and the cooling rate was revealed analytically. Meanwhile, the γ′ morphologies evolved from spheres to cuboids, concave cuboids, octets, and dendrites as the cooling rate decreased. The evolution mechanism and stability of γ′ precipitates were proposed to control their morphology and optimize the properties of superalloys. • The width of γ channel affected the dendrite evolution direction of γ′ secondary branches were demonstrated. • The growth mechanisms of different secondary branches of dendrite γ′ were illustrated. • The different morphology evolution paths of γ′ during cooling rates were revealed. • The power exponential relationship between d s γ ′ , d t γ ′ , f , ρ d grain boundary width and cooling rates were revealed.