Reaction of Ni-Based Superalloy with Liquid Sn During Liquid-Metal-Cooled Directional Solidification

Abstract

The liquid metal cooling (LMC) process has attracted increasing attention in the investment casting industry in recent years. Liquid Sn is generally used as the cooling medium in state-of-the-art LMC processes even though Sn is known to be a detrimental element in Ni-based superalloys. Therefore, Sn contamination in superalloys has become one of the top concerns for the LMC process. In this work, the reaction between liquid Sn and a Ni-based superalloy was investigated. The detectable reaction between superalloy and liquid Sn began at approximately 500 °C, and the reaction products became complex with increasing temperature. At high temperatures beyond 750 °C, a very short contact period of less than 1 minute led to a severe surface reaction. The results were compared to the surface reaction zone of the large blade. The critical time when the superalloy casting contacted liquid Sn is obtained based on experimental observations and numerical simulations. The surface reaction will occur if the ceramic mold cracked at this point or previously. The surface contamination during LMC solidification is associated with the volume of the casting. The present results indicate that surface reaction would be avoided if the volume of the large blade is reduced to ~ 30 pct of the original size.