Synthesis, structure, and mechanical properties of Ni-Al and Ni-Cr-Al superalloy foams

Reticulated nickel foams were alloyed with 8-9 wt% Al or 14-18 wt% Cr and 5-9 wt% Al in a three-step method consisting of (i) gas-phase deposition of Cr and/or Al onto the struts of a pure Ni foam by pack-cementation at 1000 °C; (ii) homogenization at 1200 °C to remove concentration gradients and to solutionize the alloyed struts; (iii) aging at 900 °C to form γ′ precipitates within the struts. The resulting alloyed foams retain the low relative densities (less than 3%) and open-cell structure with hollow struts of the original pure Ni foams, and they exhibit struts with the γ/γ′ structure typical of nickel-base superalloys. The compressive behavior of the superalloy foams, measured at ambient temperature, is compared to model predictions. The creep behavior of the superalloy foams, measured between 680 and 825 °C in the stress range of 0.1-0.3 MPa, is discussed using two models assuming strut compression or strut bending as deformation modes.