Interaction of B and Hf with oxygen in a nickel melt at РAr = 0.1 MPa and analysis of nonmetallic inclusions

The deoxidation of complex alloyed nickel-based alloys during melting in vacuum is carried out in the presence of aluminum with strong deoxidizers B and Hf, which requires additional knowledge about the activity of dissolved oxygen. For this, the activity was investigated in model melts Ni – O – (B/Hf, 0.001 – 0.1 wt. % of each) and Ni – O – Al (5 %) – (B/Hf, 0.001 – 0.1 wt. % of each) at 1560 °C and РAr = 0.1 MPa by the method of instantaneous EMF recording using certified sensors. It was shown that a[O] with the introduction of B into the melt without aluminum is 1.3 times less than with the introduction of Hf, and for melts with aluminum, a[O] decreased 1.6 times as compared with Hf. The study of the morphology and composition of non-metallic inclusions of the Ni – O – (B/Hf) systems showed that the inclusions are located along grain boundaries, have various complex configurations and sizes from 2 to 100 μm. These phases contain Ni, Fe, Zr, S, O, as well as Hf, Pb, Bi, Si, Mg after deoxidation of Hf and an increased content of Zr after deoxidation of B.