Electric Pulse-Assisted Regulation of Carbides Morphology During the Solidification Process of Nickel-Based Superalloy
摘要
In the casting of the nickel-based IN738LC superalloy, large, elongated or chain-like carbides are typical harmful phases. The traditional methods for controlling the morphology and size of carbides mainly rely on alloy composition design, cooling rate control during alloy solidification, or subsequent heat-treatment processes. However, these approaches cannot fundamentally achieve precise control over the morphology and size of carbides, thereby limiting their ability to provide uniform dispersion strengthening in superalloy. The aim of this study is to utilize the difference in electrical conductivity between the melt and carbides to apply a pulsed electric current during the solidification process of the nickel-based IN738LC superalloy, in order to obtain uniformly refined carbides. The study found that, at a cooling rate of 50℃/min, under conditions of an electropulsing frequency of 3000 Hz and a current of 160 A, the treated nickel-based IN738LC superalloy exhibited a proportion of carbides with an equivalent diameter less than 5 μm reaching 92.9%, the proportion of carbides with an area less than 30 μm2 exceeding 95%, and achieved uniform dispersion of the carbides. On the basis of traditionally controlling only the cooling rate to limit carbide growth, the applied electropulsing introduces an additional Gibbs free energy in the nickel-based superalloy melt, reducing the critical nucleation energy and thereby increasing the nucleation rate of carbides during solidification. This promotes the formation of uniformly distributed fine granular carbides in the nickel-based superalloy. This study demonstrates that pulsed electric current provides a new approach for controlling the morphology and size of carbides.