Temperature Exposure of Single- and Double-Layer Coatings of Inconel 625 Reinforced with Ni3Al Intermetallics

Abstract

The customization of metallic alloys offers the possibility of adding functionalities to a material. Customizing alloys with a dispersion of intermetallic compounds obtained by in situ synthesis does not compromise processing and allows for the addition of functionalities to less noble alloys. However, intermetallic materials present important challenges regarding their processability by welding and forming because of low toughness, ductility, and metallurgical stability at high temperatures. Graded multilayer coatings might offer a balanced solution to the aforementioned challenges by taking advantage of a ductile matrix while the fine dispersion of aluminides reinforces hardness and metallurgical stability. This investigation addressed this challenge by processing coatings of Inconel 625 superalloy with in situ formed Ni-Al based intermetallics to increase hardness and high temperature oxidation resistance while maintaining weldability. Powder mixtures of Inconel 625, Ni, and Al elementary powders were processed as single and double-layer coatings. Inconel 625 atomized alloy was modified with a powder mixture containing 75 wt. % Ni and 25 wt. % Al. Each deposited layer had a different amount of the Ni + Al powder mixtures added to the atomized Inconel 625 alloy. The single layer coating was processed with a mixture containing Inconel 625 and 80 wt. % (Ni + Al), while the double-layer coating of the first layer was deposited with the powder mixture Inconel 625 and 20 wt. % (Ni + Al), and the second layer deposited with Inconel 625 and 80 wt. % (Ni+Al). Monel 400 substrates were used for all deposits in the study. Powder mixtures were deposited by Plasma Transferred Arc allowing the in situ synthesis of Ni-Al intermetallics without compromising weldability. For both coatings, microstructural stability was sustained until 900 °C, and at 1,100°C exposure led to some degree of oxidation, but the increased hardness due to nickel aluminides intermetallics in situ formation was sustained.