A hybrid thermal spray and sinter fusion process to apply wear and corrosion resistant coatings

摘要

Cobalt-based StelliteTM alloys such as Stellite 720 with nominal composition of Co-33Cr-18Mo-2.45C are known for their excellent wear and corrosion resistance. Applied as thin coatings, these alloys can be used for applications such as balls and seats used in the valve industry. Stellite 720 is difficult to apply by HVOF thermal spraying and to achieve fusion bonding by sintering. A hybrid HVOF thermal spray and sinter fusion process is developed to realize a thick coating with thickness greater than 0.025" (0.6 mm). In order to improve the spraying process and fusibility, the Stellite alloy composition is modified. Unlike the HVOF coating alone, the coatings formed by thermal spraying and sinter fusion are metallurgically bonded to the substrate and form a substantially continuous alloy coating on the surface of the component body. The microstructure of the hybrid processed coatings are examined and compared to HVOF coating microstructure of the same alloy. The wear and corrosion resistance of the hybrid processed coatings are evaluated. The coatings showed high hardness exceeding 60 HRC with excellent wear and corrosion resistance. Balls and seats are coated for valve applications.