Effect of Preliminary Ball Milling of Nanomodifiers on Their Efficiency in Laser Surface Treatment of Titanium

Abstract

This study examines how preliminary mechanical milling of a modifying TiN-based powder mixture affects the morphology of the CO₂ laser-treated surface, the weld pool morphology, and the cross-sectional structure of the material. Ultrafine titanium nitride particles used as nanomodifier have low wettability by liquid metal, are not entrained by its convective flows, and tend to accumulate in the subsurface layer, which makes it difficult to effectively modify the structure within the treated material. Ball milling of the modifying Ti + TiN mixture for 9 min leads to the formation of composite particles (5–7 µm) with ultrafine TiN particles uniformly distributed over their surface and volume. When the composite particles are melted by the laser beam, they turn to ultrafine TiN particles of nanomodifier coated with a thin titanium layer, which have a smaller contact angle. As a result, the particles are more evenly distributed over the weld pool and the number of crystallization centers increases, leading to the formation of a fine homogeneous structure of the material. The microhardness increases by 32%, and its standard deviation decreases by a factor of 1.5–3.0.