Formation Mechanism and Prevention of White Spots in Superalloys during Vacuum Arc Remelting: A Review

White spots are a common solidification defect in vacuum arc remelting superalloy ingot, which can cause material fracture and greatly limit the utilization in high-end applications. Poor electrode quality and unstable remelting parameters are the main reasons for forming white spots. In this article, the characteristics and formation mechanism of all kinds of white spots are summarized. The influence mechanism of electrode crack, shrinkage cavity, gas and inclusion content, fill ratio, power, arc characteristics, cooling gas, and other factors on the white spots is analyzed in detail. Through rigorous examination of formation mechanisms and influencing factors, this study establishes that white spot elimination can be effectively achieved through three primary approaches: 1) optimization of the vacuum induction melting process to produce defect-free electrodes, 2) implementation of triple melting processes instead of conventional double melting, and 3) precise control and stabilization of remelting parameters.