Surface modification of Ti-6Al-4V alloy using laser-assisted deposition of a Ti-Si compound

Pre-placed laser cladding and a mixture of 80 wt.%Ti-20 wt.%Si powder are used to produce hard coatings, containing Ti5Si3, on Ti-6Al-4V alloy substrate. The experiments are performed at three different laser scanning speeds for which a pulsed Nd:YAG laser and no shield gas are used. Optical microscopy, SEM, EDS and XRD methods, as well as microhardness measurement are used to examine the microstructural characteristics and hardness of the coating and coating-substrate interface. Crack-free coatings with metallurgical bonding to the substrate are obtained using 0.6 mm initial powder thickness. The coatings demonstrate solidified microstructures containing major dendritic and cellular Ti5Si3 phase with interdendritic/intercellular mixtures containing alpha-Ti and Ti3Al phases. The results indicate that utilizing a higher scanning speed leads to a finer distribution of Ti5Si3 phase and a higher hardness of coating, while a lower laser scanning speed may provide better control of the process. The effect of the laser scanning speed on the mechanisms of atom migration during cladding is discussed. (C) 2008 Elsevier B.V. All rights reserved.