The Effects of HVOF Coating of WC-CrC-Ni Powder on In718 and of CO2 Laser Heat Treatment on the Coating

High-velocity Oxygen-fuel (HVOF) thermal-spray coating (coating) of micron-sized WC-CrC-Ni was carried out oil an Inconel718 (In718) surface to improve the surface properties, friction and wear behaviors. During the spraying, binder metals were melted and a small portion of metal carbides, such as WC, Cr7C3 and Ni3C, were melted, partially melted, or decomposed to W2C, Cr, Ni and free carbon. A porous coating was formed by the evolution of carbon oxide gases formed by the reaction of the free carbon and the sprayed oxygen gas. For further improvement, a CO2 laser heat treatment (LH) was performed on the coating. Laser beam (10.6 mu m, continuous mode, 400 W) irradiated an oval-shaped focal spot (5 mm x 4 mm) for 0.6 s at a scanning speed 400 min/min, heating to about 950-1200 degrees C from the edge to the center of the spot. Laser tracks overlap each other 30 %. The porous coating was compacted by the LH, reducing the coating thickness by about 29 % from 280 mu m to 200 mu m and the porosity by about 7 times from 2.6 +/- 0.4 % to 0.35 +/- 0.06 %. The surface hardness of In718 (410 +/- 30 Hv) was increased more than twice to 983 +/- 101 Hv by the coating; furthermore, it was increased 45 % (1425 94 Hv) by LH for 0.6 s. The friction coefficient of the In718 surface (0.45 +/- 0.08) was reduced 29 % (0.32 +/- 0.02) and 9 % (0.29 +/- 0.03) by the coating and by the LH, respectively. The wear depth was reduced from 52 mu m to 30 mu m and to 12 mu m by the coating and by the LH, respectively. A HVOF coating of WC-CrC-Ni powder on a metal surface and a LH of the coating are highly recommended for improving the surface properties, the friction behavior and wear resistance.