Influence of yttrium and vacuum degree on the purification of K417 superalloy

K417 superalloy castings with different addition of rare earth element Y were produced by vacuum induction melting technology using Y₂O₃ crucibles under different vacuum degrees. The effects and interaction mechanisms of Y and vacuum degree on the purification of the superalloy were investigated. The results showed that high purification of K417 superalloy with 4∼5 ppm O and N was obtained after addition of Y. There was a characteristic transition during the deoxidation and denitrogenation of the superalloy when the vacuum degree changed. With the addition of 0.5 wt% Y in the alloy, the concentration of O could be reduced from 34 ppm to 8 ppm in rough vacuum and from 13 ppm to 4 ppm in high vacuum, respectively. High vacuum enhanced the chemical dissolution of Y₂O₃ crucible. The concentration of N decreased from 43 ppm to 14 ppm with the addition of Y in rough vacuum condition of 100Pa. Whereas, in high vacuum condition of 0.035Pa, the concentration of N tend to increase from 4 ppm to 7 ppm. The effect of deoxidation of Y promoted the process of denitrogenation.