Rita I. Babicheva

Inhomogeneous elastic deformation of nanofilms and nanowires of NiAl and FeAl alloys

The molecular dynamics study of the uniaxial tension of nanofilms and nanowires of NiAl and FeAl intermetallide alloys has been performed. It has been shown that such samples are elastically deformed until failure at a strain of ɛxx ≈ 0.35. There is an ɛxx interval where the homogeneous deformation is thermodynamically unstable, leading to the formation of domains with different strains. The strain-stress dependence in the thermodynamically unstable region is almost linear, but has different slopes for a nanofilm and a nanowire because of the difference in the dynamics of domain walls.

Elastic moduli of nanocrystalline binary Al alloys with Fe, Co, Ti, Mg and Pb alloying elements

Abstract The paper studies the elastic moduli of nanocrystalline (NC) Al and NC binary Al–X alloys (X is Fe, Co, Ti, Mg or Pb) by using molecular dynamics simulations. X atoms in the alloys are either segregated to grain boundaries (GBs) or distributed randomly as in disordered solid solution. At 0 K, the rigidity of the alloys increases with decrease in atomic radii of the alloying elements. An addition of Fe, Co or Ti to the NC Al leads to increase in the Young’s E and shear μ moduli, while an alloying with Pb decreases them. The elastic moduli of the alloys depend on a distribution of the alloying elements. The alloys with the random distribution of Fe or Ti demonstrate larger E and μ than those for the corresponding alloys with GB segregations, while the rigidity of the Al–Co alloy is higher for the case of the GB segregations. The moduli E and μ for polycrystalline aggregates of Al and Al–X alloys with randomly distributed X atoms are estimated based on the elastic constants of corresponding single-crystals according to the Voigt-Reuss-Hill approximation, which neglects the contribution of GBs to the rigidity. The results show that GBs in NC materials noticeably reduce their rigidity. Furthermore, the temperature dependence of μ for the NC Al–X alloys is analyzed. Only the Al–Co alloy with GB segregations shows the decrease in μ to the lowest extent in the temperature range of 0–600 K in comparison with the NC pure Al.

Effect of Grain Boundary Segregation on Shear Deformation of Nanocrystalline Binary Aluminum Alloys at Room Temperature

The paper studies deformation mechanisms of nanocrystalline (NC) pure Al and its binary alloys with various distributions of an alloying element which can be Co or Mg via molecular dynamics simulations. It is revealed that a shear deformation of the pure Al is associated with the grain boundary sliding (GBS) and their simultaneous migration. Mg atoms in grain boundaries (GBs) of an Al-Mg alloy lead to GBS which does not accompany with a grain growth, while the deformation process of the corresponding alloy with a random distribution of Mg is close to that for the pure Al. Unlike Mg, GB segregations of Co atoms detain both GBS and GB migration and result in high strength of an Al-Co alloy. On the contrary, the strength of the alloy with the Co atoms distributed randomly is very low due to the structure amorphisation leading to the ease of plastic flow.

Effect of co distribution on plastic deformation of nanocrystalline al-10.2 at.% Co alloy

Molecular dynamics is employed to study stress-strain curves obtained during high strain rate deformation of nanocrystalline Al- 10.2 at.% Co alloywith (i) randomly distributed Co atoms (Al-Co substitutional solid solution) and (ii) Co atoms segregated in grain boundaries (GBs) of the alloy. The effect of Co distribution, deformation temperature, and the presence of hydrostatic pressure on the stress-strain relation is analyzed. The results are compared to that for nanocrystalline pure Al. It is found that the strength of the Al-Co solid solution is lower than that of the pure Al, while GB segregations of Co increase its strength. The alloys, regardless of the type of Co distribution, under shear loading with no hydrostatic pressure demonstrate higher ductility in comparison with the pure Al. The shear modulus of the Al-Co alloy with the GB segregations is noticeably larger than that of the pure Al and the Al-Co solid solution in a wide range of temperatures. The results of the study show that the GB segregations of Co can have a positive effect on the mechanical properties of nanocrystalline Al.

Effect of temperature on inhomogeneous elastic deformation and negative stiffness of NiAl and FeAl alloy nanofilms

The uniaxial tension of NiAl and FeAl intermetallic alloy nanofilms at different temperatures has been investigated by the molecular dynamics method. It was previously shown that nanofilms at 0 K are elastically deformed by almost 40% and that, under strain-controlled tension, there is a region in the stress—strain curves, where an increase in the strain is accompanied by a decrease in the tensile stress, i.e., the stiffness of nanofilms is negative. Deformation of the films in the thermal instability region is associated with the appearance of domains with different elastic strains. The influence of the temperature on these effects is investigated. Particularly, it is shown that as the temperature increases, both the elastic strain and the negative stiffness of nanofilms decrease. The inhomogeneous elastic strain and negative stiffness for FeAl films are observed in a broader temperature range (to 1000 K) than for NiAl films (to 300 K), which constitutes 0.16 and 0.65 of the melting point of these materials, respectively.

Deformation of nanocrystalline binary aluminum alloys with segregation of Mg, Co and Ti at grain boundaries

The influence of the temperature and sort of alloying element on the deformation of the nanocrystalline (NC) binary Al alloys with segregation of 10.2 at % Ti, Co, or Mg over grain boundaries has been studied using the molecular dynamics. The deformation behavior of the materials has been studied in detail by the simulation of the shear deformation of various Al bicrystals with the grain-boundary segregation of impurity atoms, namely, Ti, Co, or Mg. The deformation of bicrystals with different grain orientation has been studied. It has been found that Co introduction into grain boundaries of NC Al has a strengthening effect due to the deceleration of the grain-boundary migration (GBM) and difficulty in the grain-boundary sliding (GBS). The Mg segregation at the boundaries greatly impedes the GBM, but stimulates the development of the GBS. In the NC alloy of Al–Ti, the GBM occurs actively, and the flow-stress values are close to the values characteristic of pure Al.