EFFECT OF PREPROCESSING OF NANOMODIFIERS ON THEIR EFFICIENCY IN LASER SURFACE TREATMENT OF TITANIUM

Abstract

This study examines the influence of the mechanical processing of a titanium nitride based powder mixture on the change in the morphology of the CO2 laser treated surface, the weld pool morphology, and its cross-sectional structure. Ultrafine titanium nitride particles used as nanomodifier, which have low wettability in the metal melt and are not entrained by its convective flows, accumulate in the subsurface and reduce the structural modification efficiency in the bulk of the treated material. Processing of the modifying Ti + TiN mixture for 9 min leads to the formation of composite particles (5-7 pm) in which ultrafine titanium nitride particles are uniformly distributed over the surface and volume. The composite particles melt during laser irradiation and form ultrafine titanium nitride particles of nanomodifier cladded 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.