Combined Rayleigh–Taylor–Kelvin–Helmholtz instability and its role in the formation of the surface relief of the coating/substrate

The paper reports on an undulating topography initiating on the interface “coating/substrate material” under heterogeneous plasma flows to be generated by an explosion of yttrium powder on the titanium base. We assumed that an undulating topography on the interface resulted from a combination of Rayleigh–Taylor and Kelvin–Helmholtz instabilities. A flow of an incompressible viscous two-dimensional fluid was considered in the field of bulk forces. The first layer made up of titanium or silumin is thought to be static, and the second one is accelerated perpendicular to the base material plane. A range of transversal velocities in the second layer was determined, varying 0 to 55 m/s for systems Ti-Y. Navier–Stocks equation and boundary conditions were stated for each layer. In a system Ti-Y Rayleigh–Taylor instability dominates at a transversal velocity of below 10 m/s, changing into Kelvin–Helmholtz instability at velocities above 10 m/s. The study highlights importance of the transversal velocity in yttrium layer for reasoning of undulating pattern formation on the interface “coating/base material” and distribution of yttrium particles in depth of the modified layer.The paper reports on an undulating topography initiating on the interface “coating/substrate material” under heterogeneous plasma flows to be generated by an explosion of yttrium powder on the titanium base. We assumed that an undulating topography on the interface resulted from a combination of Rayleigh–Taylor and Kelvin–Helmholtz instabilities. A flow of an incompressible viscous two-dimensional fluid was considered in the field of bulk forces. The first layer made up of titanium or silumin is thought to be static, and the second one is accelerated perpendicular to the base material plane. A range of transversal velocities in the second layer was determined, varying 0 to 55 m/s for systems Ti-Y. Navier–Stocks equation and boundary conditions were stated for each layer. In a system Ti-Y Rayleigh–Taylor instability dominates at a transversal velocity of below 10 m/s, changing into Kelvin–Helmholtz instability at velocities above 10 m/s. The study highlights importance of the transversal velocity in yttriu...