Forced Chemical Mixing in Alloys Driven by Plastic Deformation

Abstract

Molecular dynamics simulations of forced atomic mixing in crystalline binary alloys during plastic deformation at 100 K are performed. Nearly complete atomic mixing is observed in systems that have a large positive heat mixing and in systems with a large lattice mismatch. Only systems that contained a hard precipitate in a soft matrix do not mix. The amount of mixing is quantified by defining a mean square relative displacement of pairs of atoms, sigma(2)(R,t), that were initially separated by a distance R. Analysis of sigma(2)(R,t) and visual inspection of the displacement fields reveal that forced mixing results from dislocation glide, and that it resembles the forced mixing of a substance advected by a turbulent flow. Consideration of sigma(2)(R,t) also provides a rationalization of compositional self-organization during plastic deformation at higher temperatures.

Hallmarks of mechanochemistry: from nanoparticles to technology

“…In this regard, it is worth noting that the average duration of collisions, of about 1 ms or less, 111 is considerably longer than the time interval underlying the local transformations induced by strain, which roughly occur in 1 to 10 ns. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] It follows that a given collision can activate various local deformation processes. Also, any given local process activated by a given collision can reach completion before the successive collision takes place.…”

Dissolving Equilibrium-Immiscible Elements via Severe Plastic Deformation

“…The first observation is that for most runs (see Ref. 40 for details) the value tends to zero, i.e., nearly complete atomic mixing.…”

“…40) In the histogram of the change of separation distances, they found peaks centered at values corresponding to the modulus of the Burgers vectors of partial dislocations and perfect dislocations, respectively. In other words, such MD simulations illustrate that it is the slip mediated by dislocations that mixes the constituent elements, disregarding the magnitude of positive heat of mixing.…”

“…Most recently, Odunuga et al 40) advanced this idea, by performing molecular dynamics simulations of forced atomic mixing in crystalline binary alloys during plastic deformation at 100 K. Configurations were created, with a B precipitate (a sphere 4.0 nm in diameter) in an A matrix (32,000 sites on a face centered cubic lattice, thus of edge length of 7.3 nm, and cube edges along the h100i directions). Compressive strains were cyclically applied along the normals of the simulation cell faces by scaling atomic positions at a constant strain rate of 5 Â 10 9 s À1 .…”

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

“…On the microscopic scale, physical and chemical transformations take place consequent to the forced mixing of chemical species, mediated by mass transport processes involving the athermal displacement of both individual atoms and relatively large atomic clusters [8][9][10][11][12][13][14][15][16][17][18].…”