Effect of titanium carbide concentration on the morphology of MC carbides in pulsed laser surface alloyed AISI H13 tool steel

In this study, TiC-AISI H13 composite coatings were produced by pulsed laser surface alloying technique. To evaluate the growth morphology of MC carbides, layers of TiC powder with different thicknesses were pre-placed on the surface of steel and then subjected to laser irradiation. X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) were used to identify the phases and scanning electron microscopy (SEM) was used to evaluate the microstructure. The results showed that TiC particles dissolved in the molten pool during laser alloying, and different morphologies of MC carbides precipitated during the cooling cycle. Thermodynamic calculations revealed that the precipitation temperature of primary MC carbides raised by increasing concentration of titanium and carbon in the melt. At a constant cooling rate, increasing the thickness of the preplaced layer caused extended growth time of the primary MC carbides. Therefore the probability of formation of radially branched and fully developed dendrites increased. Less dissolved TiC particles and lower precipitation temperatures of primary MC carbides led to the formation of particles with cross-shaped, multifaceted, and petallike morphologies. Rod-like and Chinese script-shaped secondary MC carbides located in the intergranular regions of the matrix and their morphologies were not affected by the chemical composition of the molten pool.