Model of Formation of Nanocomposite Layers on Metal Surfaces by Electro-Explosive Alloying

Abstract

The paper presents a new mechanism for the formation of a nanostructured layer in the near-surface alloying zone during pulsed plasma treatment of metals. The mechanism is based on the Kelvin–Helmholtz (KH) instability, which occurs at the interface between the plasma and the melt. The KH instability leads to the formation of waves at the interface, which then disintegrate into small droplets. These droplets are solidified to form a nanostructured layer. The proposed mechanism allows us to explain the penetration of alloying elements into the depth of the alloying zone and more uniform alloying compared with traditional methods. To quantify the mechanism, a dispersion equation for the KH problem is obtained, taking into account viscous and capillary stresses in the melt. The dependence of the increment on the wavelength of surface disturbances is analyzed. The increment is shown to have a maximum in the nanometer range at a relative plasma and melt velocity in the range of 100–1000 m/s, achieved under processing conditions. A model is proposed to explain the undulating nature of the interface between the zone of electroexplosive alloying (EEA) and the metal base. The model is based on the development of the KH instability at the melt–plasma interface; resonant interaction of KH waves with inhomogeneities of the interface. Numerical calculations have been carried out, which confirm the proposed mechanism. The dependence of the amplitude of the boundary oscillations on time is obtained. The process of blurring the boundary due to percolation mixing is described.