Solidification and phase transformation in AISI 1045 steel laser surface alloyed with TiC

Laser technology enables melting and alloying of specimen surfaces without the substrate itself being heated, whereby surfaces with special attributes are obtained with the properties of the substrate remaining unaffected. The surface of AISI 1045 steel was laser-alloyed with TiC powder, using a CO₂ laser of 2.5 kW maximum power. Particles of TiC were injected into the molten surface layer, forming a composite material, steel + TiC. Some of the particles partially melted during their passage through the laser beam and re-solidified, forming small and fine dendrites of different types. Identification of phases by TEM and diffraction of electrons revealed the presence of tetragonal TiC and orthorhombic (FeTi)C. Mössbauer results show ternary Fe-Ti-C phases, which can be related to the TEM results. A sample having a composition of 60wt%Fe-32wt%Ti-8wt%C was prepared by arc melting of elements’ powder. The sample was subjected to TEM and Mössbauer analysis before and after annealing. The results show a correlation between the phases that were identified in the laser treated sample, and the composition controlled sample. An explanation of the formation of the different phases, based on thermodynamic considerations, is presented.