Model of nanostructure formation in Al–Si alloy at electron beam treatment

The paper reports on analysis of mechanisms and development of a mathematical model describing the effect of low-energy high-current electron beams on eutectic Al–Si alloy. The paper highlights the relationship between the effect of electron beams and formation of a gradient multilayer structure in the item to be treated. The surface layer has a structure of columnar crystallization; its cross sizes vary 200 to 600 nm. The principal mechanism forming the columnar structure is suggested to be a thermocapillary instability arising due to the gradient of temperature in the melted layer. It leads to vortices, pointing this way at formation of a structure with cellular crystallization. The linear analysis of this instability versus weak harmonic disturbances revealed that the wavelength with the maximal disturbance decrement is almost similar to the cross sizes of crystallization columns.