Nonuniform Elastic Deformation of Nanofilms Formed from Nial and Feal Alloys

Abstract

Using MD techniques, uniaxial tension of nanofilms made from NiAl and FeAl alloys is investigated at different temperatures. It is found out that the films undergo elastic deformation to fracture at the strains within 35–40 %. The stress-strain curves from these films constructed for the strain-controlled tensile loading contain a region where the increase in strain is accompanied by a decrease in tensile stress, which suggests a negative rigidity of the films. The deformation of these nanofilms in the region of low thermodynamic stability and instability is attributed to the formation of domains with different elastic strain values. As the temperature is increased, both the deformation to fracture and the negative rigidity decrease. For FeAl, nonuniform elastic deformation and negative rigidity are observed in a wider temperature range (up to 1000 K) than for NiAl (up to 300 K), which is 0.65 and 0.16 of their melting temperatures, respectively. An introduction of prismatic dislocation loops into the structure of nanofilms gives rise to their hardening due to generation of internal stresses resulting in compression of the surface layers.