Negative stiffness of the FeAl intermetallic nanofilm

Uniaxial tension of the nanofilm of the FeAl intermetallic alloy has been simulated by the molecular dynamics method. It has been found that the nanofilm is elastically deformed by 37%. There is a region in the stress-strain curve, where the strain increases with a decrease in the tensile stress, which indicates the negative stiffness of the nanofilm in this region. The uniform strain with a decrease in the tensile stress is unstable thermodynamically, which leads to the appearance domains with different elastic strains in the nanofilm. The deformation in the unstable region develops due to the domain-wall motion; as a result, the domains with a higher strain grow at the expense of the domains with a lower strain. A similar deformation mechanism was recently described by Savin with coworkers for the DNA molecule.