Intermetallic Alloys Based on γ'Ni3Al: Part I. Features of the Structure, Formation of (γ' + γ) Structures, and Alloying

Abstract

γ'Ni₃Al-based casting alloys have a lower density, higher melting point and resistance to oxidation, and a higher ceiling of operating temperatures than modern heat-resistant nickel alloys. The article discusses the features of the electronic structure and crystallization of domestic (such as VKNA/VIN) and the most advanced foreign (γ' + γ) low-alloyed γ'Ni₃Al-based alloys (IC type), and experimental data on the nature of the structures formed during directional crystallization of alloys with different types of alloying and on the nature of the distribution of components in the γ'Ni₃Al and γNi phases and structural components in the cellular-dendritic structure of single crystals with 〈111〉 and 〈001〉 crystallographic orientation are presented. The influence of heat treatment on the microstructure, distribution of alloying elements, and mechanical properties of the VKNA type alloys is investigated in a wide range of temperature–time parameters. A comparative analysis of the effect of temperature and duration of heat treatment and cooling rate after heat treatment on the heat resistance of alloys showed that, unlike other Ni₃Al-based alloys, for single crystals from the VKNA type economically alloyed alloys and parts made from them (uncooled working blades of aviation gas turbine engines, nozzle apparatuses, jet nozzle spacers, and other parts of the hot path of gas turbine engines), a short-term heat treatment (1150°C/1 h) is necessary and sufficient to relieve casting stresses. The alloys demonstrate high heat resistance at 1100–1200°C and the ability to withstand short-term casting temperatures up to 1250–1300°C.