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The microstructural and chemical evolution after different processing steps of Ta-containing NiCoCrAlY bond coats (BC) sprayed by high velocity oxy-fuel on Ni-base superalloy (SA) substrates, top-coated with 7YSZ and furnace cycled at 1100 ºC focusing along the BC/SA interfaces is presented. Three superalloys were selected considering their Ta content relative to that within the BC: a) no Ta in the superalloy composition (IN100) and either b) similar or c) higher Ta content with respect to the BC (M247LC SX and CMSX-4, respectively). The processing conditions were as-sprayed, as-annealed, after EB-PVD deposition of a 7YSZ top coat, and after furnace cyclic tests (1100 ºC /120 h). The evolution of chemical composition after the different process steps are presented that include a normalization criteria to a Ni-Al-Cr system, elemental profiles as well as Weibull distribution plots of minor containing elements such as Ti, Ta, Mo, or W at the BC/SA interface. The effect of Ta was activated in some coated substrates by the presence of Ti and C in the superalloy consisting of inward Ta-diffusion, trapping of outward diffusing Ti and the subsequent formation of (Ta, Ti)-rich carbides in the BC avoiding possible segregation effects as titanium oxide in the oxide scale.

Changes in composition, crystal structure and phase transformations of B2-(Ni,Pt)Al coatings upon isothermal oxidation experiments (natural and scale free oxidation) at 1100 • C, as a function of time beyond their martensitic transformation, are reported. Specifically, the analysis of lattice parameter and composition are performed to identify changes in the B2-(Ni,Pt)Al phase upon the chemically-driven L1 0 -(Ni,Pt)Al and L1 2 -(Ni,Pt) 3 Al transformations. The B2-(Ni,Pt)Al phase was found to disorder and transform the martensite during the heat treatments for both oxidation experiments at approximately 36.3 and 40.9 at. % of Al, 47.7 and 42.9 at. % of Ni, 6.2 and 8.5 at. % of Pt, 4.2 and 2.9 at. % of Cr and 4.4 and 3.8 at. % of Co. The lattice constant and the long-range order parameter of the B2-(Ni,Pt)Al phase decreased linearly as a function of the elemental content irrespective of the nature of the oxidation experiments.

IN718 is a Ni-based superalloy usually manufactured by conventional processes such as wrought or casting. However, recently additive manufacturing (AM) technologies, such as Powder bed fusion (PBF), are used to produce IN718 parts. Heat treatments, also designed for conventional processes, are usually used in AM parts to improve mechanical properties. Unlike traditional techniques, AM processes involve rapid cooling rates, large thermal gradients, and multiple reheat cycles, which might cause high residual stresses and elemental segregations in the printed parts affecting their final mechanical properties. In this work, a detailed comparative study of microstructural features was carried out in both wrought-and PBF-produced IN718. It was found differences in size, shape, and location of MC carbides. According to experimental results and the phase fraction diagram obtained from Thermo-Calc, these MC carbides cannot be dissolved in a conventional solution heat treatment. In consequence, these carbides continue their evolution during complete aging heat treatment, affecting the material hardness. Nevertheless, similar hardness in the wrought and AM sample was obtained after applying a modified aging treatment proposed in this work.