Grain size effects on the mechanical behavior of open-cell nickel foams

The dependence of the mechanical-behavior of nickel foams upon their grain size was studied. First, the grain coarsening phenomenon which occurs during the processing of foams was analyzed. A metallurgical characterization of the grain growth during heat treatment was performed: The grain size effects on the mechanical properties was then studied, namely, via the Hall-Petch law. The foam walls being very thin, roughly 10 mum in thickness, grain growth and mechanical behavior might be different compared with conventional materials. The present results obtained with foams were compared with literature data on bulk pure nickel and with nickel foils of 10 and 50 mum in thickness which are good candidates for the modeling,of the cell walls. The EBSD technique allowed observing the absence of preferred crystallographic orientations for both foams and foils. A mechanical model in the spirit of that by Gibson and Ashby was finally presented incorporating the grain size effect on yield strength and hardening modulus. This model provided a good estimation of the experimental data.