Effect of Ta on the microstructure and hardness of Stellite 6 coating deposited by low power pulse laser treatments

Stellite 6 hardfacing alloy with different Ta contents is successfully synthesized with an in situ process on low carbon ferritic steel substrate by Nd:YAG pulsed laser cladding with pre-placed Stellite 6 and Ta mixed powders. The effect of different amounts of Ta on the microstructure of the Stellite 6 hardfacing alloy is investigated using scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. With an increase in Ta content, in addition to orthorhombic Cr-rich M7C3 carbides observed in the Ta-free Stellite 6 alloy in interdendritic regions, Ta-rich M4C3.04 type carbides are formed as well as individual bulky Ta-rich MC type carbides in Chromium carbide–Cobalt solid solution eutectic area. Furthermore, the Co-rich dendrites become much finer. With further increase of Ta, hexagonal M7C3 carbides are formed at the interface of orthorhombic ones. These microstructural changes are responsible for the improvement of the hardness of the Ta modified Stellite 6 hardfacing alloy.