Influence of yttrium on purification and carbide precipitation of superalloy K4169

The effect of reactive element yttrium on purification and carbide precipitation of superalloy K4169 has been studied through vacuum induction melting. The results show that yttrium has a strong deoxidizing and desulfurizing ability, and the impurity elements of sulfur and oxygen in melting K4169 are greatly reduced to 2-5 ppm and 4-5 ppm, respectively. The metallurgical reaction product is mainly Y2O3 and yttrium containing sulfides have not been observed. With the increase of the content of yttrium from 0.005 wt.% to 0.033 wt.%, the morphology and size of MC carbides in casting are significantly influenced due to that the yttrium changes the diffusion of the carbide forming elements and solid fraction during solidification. In the alloys without yttrium, only isolated blocky or strip carbides exist, while skeleton-like carbides are observed in the alloys with yttrium. Both the average size and the number density of skeleton carbides decrease monotonously with yttrium content increasing. After yttrium increasing to 0.033 wt.%, a phase of hexagonal Ni17Y2 is observed to precipitate in the form of symbiosis with MC carbide and matrix. The addition of yttrium is not beneficial for the properties of K4169 alloys at the room temperature, which is quite related to the MC carbides with a large skeleton-like morphology through the analysis of tensile fracture. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.