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The oxidation behaviors of the Ni-22Cr-14W-2Mo superalloys with various La contents were investigated at 1 000℃and 1 100℃up to 500 h.The experimental results show that the oxidation resistance is improved by La addition.The mechanism of the reactive-element effect(REE) exhibits some difference at various oxidation temperatures.The REE is dependent on the solutionized La content when the alloy is oxidized at 1 000℃.The dispersed LaCrO_3 segregates on the grain boundaries of Cr-oxides.and hence the diffusion of metallic ions,e.g.,Mn~(2+) and Cr~(3+),are prevented.The oxidation resistance decreases with the increase of La content. However,the REE ascribes not only to the solutionized La,but also to the La-Ni intermetallic phases,when the alloy is oxidized at 1 100℃.The oxidation resistance is influenced by two effects:firstly,the formation of the dispersed La_2O_3 from the solutionized La on the grain boundary of Cr-oxides reduces the oxidation rate,and secondly,the aggregation of the La-O oxides from the large amount of La-Ni phases accelerates the oxidation process.The alloy with 0.026%La(mass fraction) exhibited excellent oxidation resistance at 1 100℃.
The oxidation behaviors of the Ni-22Cr-14W-2Mo superalloys with various La contents were investigated at 1 000 ° C and 1 100 ° C up to 500 h. The experimental results show that the oxidation resistance is improved by La addition. The mechanism of the reactive-element effect (REE) exhibits some difference at various oxidation temperatures. The REE is dependent on the solutionized La content when the alloy is oxidized at 1 000 ° C. and therefore the dispersed LaCrO 3 segregates on the grain boundaries of Cr-oxides. However, the REE ascribes not only to the solutionized La, but also to the La-Ni intermetallic phases, when the alloy is oxidized at 1 100 ° C. The oxidation resistance is influenced by two effects: firstly, the formation of the dispersed La 2 O 3 from the solutionized La on the grain boundary of Cr-oxides reduces the oxidation rate , and secondly, the aggregation of the La-O oxides from the large amount of La-Ni phases accelerates the oxidation process. The alloy with 0.026% La (mass fraction) exhibited excellent oxidation resistance at 1 100 ° C.