Interaction of praseodymium and dysprosium with oxygen in nickel melts at РAr = 0.1 MPa and analysis of nonmetallic inclusions

The interaction of Pr/Dy with oxygen in nickel melts at РAr = 0.1 MPa and constant temperature was studied by the method of instantaneous EMF fixation using a Mo[Cr/Cr2O3//ZrO2(MgO)//O(NiL)]Mo cell and certified sensors. Dependences a[O] = f[Pr/Dy, %] were expressed as logarithmic equations, which made it possible to compare them with each other in the concentration range of 0.001 – 0.2 % of each deoxidizer and determine that the deoxidizing capacity of Pr is 1.7 times higher in terms of compared to Dy. Calculated a[O] in Ni – O – Al – (Pr/Dy) melts compared to Al at a concentration of 0.05 % elements and showed a seven-fold decrease for the first deoxidizer and an eleven-fold decrease for the second. The morphology of non-metallic inclusions in metallographic sections of Ni – O – Pr/Dy alloys indicates that the inclusions are located along grain boundaries and have different configurations and complex heterophase composition. The analysis of non-metallic inclusions with the maximum content of the deoxidizing element proved the existence of Pr/Dy oxygen compounds, which confirms the data of thermodynamic and mass spectrometric studies. The average content of Zr in non-metallic inclusions during the deoxidation of Pr is twice as high as in the experiments during the deoxidation of Dy, which indicates the interaction of Pr/Dy with ZrO2 of the EMF sensor and the predominant interaction of Pr compared to Dy and correlates with the data on the determination of a[O].