Effect of Laser Processing Parameters on Microstructure, Hardness and Tribology of NiCrCoFeCBSi/WC coatings

Ni alloys possess high strength and toughness along with a resistance to corrosion and wear in a wide range, which is mainly predetermined by the alloying system [2]. WC pos-sesses a high melting point (2600–2850 °C), high fracture toughness (28 MPa∙m1/2) and high hardness (16 - 22 GPa) [3]. It is widely recognized as well that cemented tungsten carbide, which is usually used in coatings, has some degree of plasticity, especially when compressive loads are applied [4]. Moreover, it is showed that at the later deformation stage dislocations’ density of WC in cermets dominates, indicating a more important WC role in the plasticity than a role of a metal binder [5]. This gives an advantage to WC over brittle hard materials. For depositing protective Ni-WC coatings, thermal spraying methods are widely used, including flame spraying (FS), plasma transferred arc (PTA) spray, arc spraying, high-velocity oxygen fuel (HVOF) spray – mainly using powder materials. In the last two decades, the main attention has been paid to the development of laser methods for the deposition of Ni-WC coatings [6-30]. Two main methods can be distinguished - laser re-melting of previously sprayed layers [6-8] and, actually, coating formation using laser beam energy (also known as laser cladding) [9-30]. During the laser cladding, the stream of powdered material or wire is fed onto the substrate surface (or powder is pre-placed there) under the laser beam, which generates a melted pool. Laser moves over the surface and by one individual pass forms narrow coat-ing's layer. To coat the entire surface, the process typically is performed pass-by-pass with some pass overlapping.