Frédéric Diologent

Temperature dependence of lattice mismatch and gamma" volume fraction of a fourth-generation monocrystalline nickel-based superalloy

Abstract The strain distribution in a new generation nickel-based single crystal superalloy has been determined in the temperature range 293K–1598K. Measurements have been performed using diffraction of high energy synchrotron radiation (150keV, λ = 0.008 nm) to determine the variations with temperature of the γ/γ′ lattice mismatch and of the γ′ volume fraction. The chemical segregation at the dendrite scale and the internal stress induce a large range of values for the lattice mismatch. The measurements of the γ′ volume fraction determined by X-ray diffraction are in agreement with those obtained by atom probe tomography, image analysis or computation.

Microstructure, Strength and Creep of Aluminium-nickel Open Cell Foam

Al–6.4 wt% Ni open-cell foams produced by replication are tested in compression and in tension at room temperature and creep tested in tension at 450°C. The mechanical behaviour of this foam at room temperature is consistent with that observed for other open-cell metallic foams. A strong dependence on relative density as well as dependence on stress and temperature of the steady-state creep rate are captured by the model described by Mueller et al. [Scripta Mater. 57 (2007) p.33], itself a simplification of variational estimates by Ponte Castañeda and Suquet [Adv. Appl. Mech. 34 (1998) p.171]. The foam exhibits two regimes of creep, separated by a critical stress; these features can be interpreted on the basis of the microstructure of the Al–6.4 wt% Ni alloy making the foam. This microcellular eutectic Al–Ni exhibits attractive creep failure resistance compared to other open-cell aluminium alloy foams.

Uniaxial deformation of microcellular metals: model systems and simplified analysis

Microcellular aluminium can be produced by a process known as replication; this involves the infiltration of a packed bed of NaCl particles which are subsequently leached after metal solidification. The resulting material features a uniform distribution of equisized pores, the shape and volume fraction of which can be tailored, as can the composition and microstructure of the metal making the resulting metal “sponges”. These display a regular uniaxial stress-strain behaviour, at both room and elevated temperature, which is interpreted using standard composite models for Young’s modulus coupled with variational predictions for non-linear deformation of two-phase composites by Ponte-Castaneda and Suquet, adapted and simplified for the specific case at hand.