Microstructure and surface properties of laser-remelted titanium nitride coatings on titanium

Laser remelted tracks were produced on the surface of titanium nitride (TiN) coated titanium. In order to produce different microstructures, seven conditions were tested by varying laser power and speed. The remelted tracks were then evaluated from the surface mechanics point of view through microhardness and sliding friction tests. Samples produced in conditions where laser speed varied from 5 to 100 mm/s presented high TiN surface content and increased hardness. In the velocity range of 20-100 mm/s, the remelted tracks presented high resistance to wear. The dendrites tend to coalescence when the scanning velocity is below 2 mm/s. The low velocity experiments (1 and 2 mm/s) presented eutectoid decomposition of the TiN/Ti phases creating a Ti2N phase at boundaries, which decreased the hardness and the wear resistance at surface. The results indicated that the best condition in terms of surface properties is obtained when the scanning rate is 5 mm/s and the laser power is 500 W.