Graded Inconel 625 coatings with in-situ processing of Ni3Al

Abstract

Ni superalloys have been widely used to process coatings due to a bouquet of attractive properties in a wide range of temperature. However, higher performance Ni alloys are typically those that offer larger processing challenges. Materials systems have been studied to mitigate this challenge. In hardfacing coatings multilayers have been processed both to reduce the detrimental effects of dilution with the substrate and to enhance the resistance to crack propagation, the latter of particularly relevance when depositing alloys reinforced with hard particles with a reduced weldability but that offer enhanced performance at the surface. The present study addressed the effects of customizing a commercial Inconel 625 atomized alloy, with increasing additions of Ni and Al elemental powder mixtures, to obtain multilayered coatings with a composition and property gradient. The gradual additions of Ni + Al powder mixture to the IN 625 atomized alloy allow for the in-situ synthesis of aluminides while maintaining good weldability, increasing mechanical properties and oxidation resistance. Results show a continuous solidification microstructure, crack-free multilayer coatings with smooth chemical composition profiles and property gradient. A gradual change on the strengthening mechanisms is identified, from solid solution on the first layer of IN 625 to a mixture of solid solution and Ni3Al precipitate dispersion on the top layer processed with the feedstock richer in the Ni + Al powder mixture. These changes induced increasing elastic modulus, hardness and oxidation resistance at 1300 °C following the chemical composition gradient in coatings.