In a polycrystalline γ-γ' nickel-based superalloy, γ' precipitates with a close-to-twin orientation relationship to their surrounding matrix (named T-type precipitates) are found in recrystallized grains located near specific unrecrystallized grains (named recovered grains). This type of γ/γ' interface has not been reported in literature before. Inherited from the ingot conversion process, recovered grains are characterized by a high density of micrometric and close-to-coherent γ' precipitates. Resulting from the interaction of the recrystallization front with the latter precipitates, the T-type precipitates appear to form onto the recrystallization front. The present paper details the crystallographic characteristics of the T-type precipitates. KeywordsGamma -Gamma Prime nickel-based superalloy, Interphase boundary, Twin boundary, Recrystallization.Polycrystalline γ-γ' nickel-based superalloys are commonly used to manufacture aircraft engine rotative parts due to their good mechanical behavior at high temperature (tensile, fatigue, creep resistance) [1]. Parts are usually derived from cast ingots through forging sequences [2,3]. They are made of a γ matrix in which γ' precipitates of various sizes are distributed. Both γ and γ' phases have a cubic structure but, while the γ phase is a Face Centered Cubic (FCC) non-ordered solid solution, the γ'-Ni 3 (Al,Ti) phase has a L1 2 ordered structure. Yet, the mechanical properties of the alloy do not only depend on the size and spatial distribution of the precipitates [4], but also on the γ/γ' interface characteristics [5,6]. Indeed, γ' precipitates are reported in literature as coherent, semi-coherent or incoherent to their surrounding matrix [7]. Coherency means that the γ and γ' crystal lattices perfectly coincide at the γ/γ' interface. This is made possible by a low lattice parameter mismatch between the γ and γ' phases [8]. Coherent γ/γ' interfaces have very low energies [9,10] and form during the cooling stages of the forging process for example. However, if some misfit dislocations pile up at the γ/γ' interface, the lattice matching is only partial and the interface is semi-coherent [7]. Semi-coherency occurs when external stresses (high temperature plastic deformation) or internal stresses (e.g. induced by long aging treatments leading to particle coarsening) generate dislocation loops which are incorporated into the γ/γ' interface as misfit dislocations [11]. Finally, when there is no crystal lattice matching, the γ/γ' interface is incoherent and has a high energy [9]. Secondary γ' precipitates which form during the cooling stages of the forming process, are coherent with a cube-cube orientation relationship: they evolve from spheres to {100} bounded cubes as their size and/or the lattice misfit increase [12]. On the other hand, primary γ' precipitates, derived from the as-cast microstructure and high temperature billet forging sequences, are usually incoherent with no special orientation relationship, excepted in case of heteroepitaxial recrystallizat...

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