MOLECULAR DYNAMICS SIMULATION OF THE EFFECT OF ULTRASONIC VIBRATIONS ON THE STRUCTURE OF NONEQUILIBRIUM [112] TILT GRAIN BOUNDARIES IN NICKEL.

The effect of ultrasonic vibrations on the structure of nonequilibrium symmetric [112] tilt grain boundaries (GBs) in nickel containing dipoles of wedge disclinations is studied by means of molecular dynamics simulations. As an example, symmetrical Σ = 15 / 78.46° tilt boundary is considered. It is shown that above some critical amplitude of the applied oscillating tensile stress the GB acts as a source of lattice dislocations the generation of which relaxes the internal stresses and excess energy associated with the disclination dipole. After several cycles of vibrations the GB fully recovers its equilibrium structure free of defects and long range stresses. It is concluded that the emission of lattice dislocations is an important mechanism, which leads to a number of effects related to structure relaxation in ultrafine grained materials under ultrasonic treatment observed in experiments. [ABSTRACT FROM AUTHOR]