Solidification Behavior and Fine Grain Control of Ti-Al-Si Coating by Electrostatic Field Assisted Direct Laser Deposition

The microstructure of Ti-Al-Si coatings prepared by direct laser deposition (DLD) requires further refinement and homogenization to enhance coating performance. In this study, an electrostatic field (EF) was introduced to assist the DLD process, and a thermal-flow-electrical multiphysics coupling model was established using COMSOL Multiphysics 6.3 software. The solidification behavior of the molten pool under the EF was investigated, focusing on the mechanism by which the EF influences the nucleation and growth of grains and reinforcing phases. Experimental results revealed that the external EF disrupted the molten pool flow, thereby altering the internal heat dissipation mechanism and affecting the morphology and size of the solidified grains. Under an external EF of 150 V/cm, the coating exhibited the most refined grains, with an average size of 0.417 μm (a 46% reduction non-EF). Concomitantly, the application of the EF increased the concentration of Ti4+ and Si4+ ions at the solid–liquid interface, promoting the formation of a substantial quantity of Ti5Si3 reinforcing phases. The average microhardness of the coating reached 1393 HV0.2, which is 21% higher than that of the coating without an EF. The surface roughness decreased to 0.551 μm, with a minimum wear percentage of 1.4%. Moreover, the EF modified the wear mechanism of the DLD Ti-Al-Si coating. The findings of this study hold scientific significance and practical value for advancing DLD-fabricated high-performance titanium alloy components, offering critical insights into microstructure optimization and process control strategies.