Effect of rare earth oxides on desulfurization reaction at CaO ceramic surface during smelting of Ni-based superalloy

The surface desulfurization reaction mechanism during smelting of Ni-based superalloys with CaO, REO and CaO-REO ceramic system was investigated. By means of SEM-EDS, EPMA, XRD and XPS, surface layer mixed with CaS and 12CaO.7Al2O3 are found after the reaction between CaO and melt. CaS was the product after desulfurization and 12CaO.7Al2O3 was the intermediate transfer medium connected CaO and alloy melt at 1500 degrees C. Pure REO have no effect on desulfurization, only react with active element Al in superalloy to form binary oxides of RE and Al. The addition of REO in CaO will change the transfer medium of the interface and cause stratification. The desulfurization product CaS is in the outermost layer and the transfer medium Cax-REyAlzOm is in the middle layer.