The Effects of Rare Earths and Reactive Elements on the Oxidation Resistance of Ni–20Cr Alloy

Abstract

The isothermal oxidation behavior of Ni-20Cr alloys with 0.7mass% of various reactive elements (Y, La, Al, Zr, Ti and Si) was investigated in air at 1273 and 1373K.It was found that the alloying elements except for Ti reduced the oxidation rate of the Ni-20Cr alloy at 1273 and 1373K. There was a tendency that the parabolic rate constants obtained during the first 36ks oxidation at both temperatures for the alloys with the alloying elements except for Ti were closely related to the affinity for oxygen of the alloying elements. The larger the standard free energy for the oxide formation of the alloying element, the smaller was the parabolic rate constant for the oxidation of the alloy with the alloying element. The oxidation behavior after 36ks oxidation at 1373K was rather complex compared to that at 1273K. The highest oxidation resistance was obtained by a Ni-20Cr-0.7Y alloy at a lower temperature (1273K) and during the early stage of oxidation at a higher temperature (1373K). Whereas, a Ni-20Cr-0.7Al alloy showed the highest

Effect of Rare Earth Oxide Dispersion on the Oxidation of Ni–15Cr Sintered Alloy

“…A similar result was obtained in the oxidation of and Fe-20Cr alloys with the addition of rare earths in the metallic form (22) (23). These results strongly suggest that the solubility of NiO or the diffusivity of Ni ions in Cr2O3 may be changed due to the introduction of rare earths.…”

Effect of Surface‐Applied Reactive Element Oxide on the Oxidation of Binary Alloys Containing Cr

“…Nagai et al (30) have shown that the addition of A1 to Ni-20 w/o Cr greatly improved the scale adherence at 1373 K. The beneficial effect of AI was found to be even better than that of La or Y additions. Mulford (31) reported that the addition of A1 to Ni was not as effective as a Cr addition to prevent sulfur segregation to grain boundaries between 900-1300 K. The results of these two studies clearly indicate that the effectiveness of A1 in a Ni-Cr alloy in improving the scale adhesion cannot be simply due to sulfur scavenging by the AI.…”

“…Mulford (31) reported that the addition of A1 to Ni was not as effective as a Cr addition to prevent sulfur segregation to grain boundaries between 900-1300 K. The results of these two studies clearly indicate that the effectiveness of A1 in a Ni-Cr alloy in improving the scale adhesion cannot be simply due to sulfur scavenging by the AI. Nagai et al (30) attributed the effectiveness of A1 to the formation of internal oxide pegs of A1203.…”

Characterization of oxidation mechanisms in a family of polycrystalline chromia-forming nickel-base superalloys

“…Effect [51,[55][56][57][58]. Many superalloys already incorporate elements such as Y, Hf, La and Zr in order to preferentially segregate to oxide grain boundaries, where they improve scale adhesion by acting as sulfur-getters, and also reduce oxidation rates by inhibiting cation transport [59].…”