冷速对IN718凝固过程中偏析和Rayleigh数的影响

利用SEM和EDS研究了在冷速分别为1,3和6K·min^-1时高温合金IN718的凝固组织、液体中Nb和Mo含量变化,并计算了液体密度差和相对Rayleigh数与温度的关系.结果表明:由于偏析,液体中Nb、Mo含量和液体密度差随着温度的降低而增加;冷速越低,Nb、Mo偏析越严重,同温度下液体密度差越大.相对Rayleigh数的计算表明,不同冷速下相对Rayleigh数都在1330℃存在最大值,随着冷速降低,其值急剧增加,黑斑形成趋势增大,大铸锭中冷速低于1K·min^-1时会形成黑斑.

Effect of cooling rate on the segregation and Rayleigh number of IN718 during solidification

The solidification microstructure of superalloy IN718 and the contents of Nb and Mo in liquid during solidification were investigated at cooling rates of 1, 3 and 6 K·min^-1 by SEM and EDS. The liquid density difference and relative Rayleigh number at different temperatures and different cooling rates were calculated. The results show that the contents of Nb and Mo in liquid and the liquid density difference increase with decreasing temperature due to segregation. The slower the cooling is, the heavier the segregation of Nb and Mo is, and the more liquid density difference at the same temperature. The maximum values of relative Rayleigh number exist at 1 330℃ at all the three cooling rates, with the decrease in cooling rate the maximum values of relative Rayleigh number raise dramatically, and freckle tendency increases. Freckles could form in large industrial ingots at a cooling rate less than 1 K·min^-1