High-Temperature β-NiAl + γ'-Ni3Al + γ-Ni Alloys of the Ni–Al–Co System

Abstract

The oxidation resistance of cast β-NiAl + γ'-Ni3Al + γ-Ni alloys of the Ni–Al–Co system in air at 1100, 1200, and 1300°C for 100 h is studied. An increase in the cobalt content from ≤5 at % (in complexly alloyed high-temperature γ' + γ VKNA alloys with ~17 at % Al and Cr, Mo, and W) to 10 at % in chromium-free β + γ' + γ alloys with 26–29 at % Al and 0.26 at % Ta, Re, Hf, and Y is shown to increase the heat resistance due to an increase in the aluminum content, an increase in the plasticity of scale, and the prevention of its exfoliation. The oxidation resistance of the base alloy decreases because of an increase in the cobalt content in the base NIAL-1 alloy from 10 to 16 at % and the introduction of 4.25 at % Cr and 0.16 at % Y of Hf. Its oxidation resistance at 1300°C, which was estimated from the weight increment per unit surface in 100 h corresponds to that of the well-known VKNA/VIN γ' + γ alloys at 1100°C. The oxidation resistance of the alloys with 16 at % Co or 4.25 at % Cr at 1100 and 1200°C is at the level of the VKNA/VIN alloys at 1000°C. The new β + γ' + γ alloys, which have higher oxidation resistance than structural high-temperature γ' + γ alloys and lower high-temperature strength, can be considered as heat- and oxidation-resistant coating-free alloys for short-term operation at 1100°C.