Nickel-base superalloys, consisting of the γ' Ni3Al phase with a L12 crystal structure embedded in the γ phase with an A1 crystal structure, are characterized by a remarkable high temperature strength and a high oxidation resistance.
A possibility to further enhance the mechanical properties could be reached by precipitation of unordered γ particles within the ordered γ' phase [1, 2]. This current work aims to investigate the effect of γ particles within the γ' phase, on the mechanical properties of a ternary Ni86.1Al8.5Ti5.4 model alloy. For this purpose a specific heat treatment, consisting of slow cooling from above the γ' solvus temperature to 940 °C, was conducted. A subsequent annealing at 750 °C allows to generate γ particles within the γ' phase. The γ particles grow with proceeding heat treatment duration. This specific heat treatment allows to assess the influence of different γ particle sizes in the γ' phase by nanoindentation (see figure 1). The hardness is found to increase up to an optimal γ particle size, before the hardness starts to drop again. Furthermore, an industrial relevant, typical γ/γ' microstructure with different γ particle dimensions inside the γ' phase was also investigated by nanoindentation and compression testing. Here also, an increase of the strength can be achieved by choosing an optimal γ particle size. Overall it was found, that a hierarchical microstructure could be used to enhance the mechanical properties of the ternary Ni-Al-Ti superalloy.
 F. Vogel, N. Wanderka, Z. Balogh, M. Ibrahim, P. Stender, G. Schmitz, J. Banhart, Nature Communications 4 (2013) 2955.
 M. Doi, D. Miki, T. Moritani, T. Kozakai, Proc. Int. Symp. on Superalloys, TMS (The Minerals, Metals & Materials Society), Warrendale, PA, 2004, p. 867–875.
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