The processing optimization and property evaluations of HVOF Co-base alloy T800 coating

Co-base alloy Tribaloy-800 (T800) powders were coated on Inconel718 (IN718) by high velocity oxygen fuel thermal spraying. The optimal coating process (OCP) was obtained via studying the surface properties of 16 coatings prepared by Taguchi program. Surface hardness and porosity were 560-630 Hv and 1.0-2.7%, respectively, strongly depending on spraying processes. The OCP of hardness was oxygen flow rate (FR) 38 FMR, hydrogen FR 75 FMR, and feed rate 30 g/min at spray distance 5 inch. The adhesion strength of T800 coating with substrate had a slight increase and the thermal shock resistance of T800 coating was improved greatly by introduction of bonding layer Ni-Cr. Friction and wear behaviors have been investigated by a reciprocating sliding test at both 25 A degrees C and an elevated temperature 538 A degrees C (1,000 A degrees F). Both friction coefficients (FC) and wear traces of the coating were smaller than those of IN718 substrate at both 25 and 538 A degrees C. FC and wear traces of IN718 and coating decreased with increasing the surface temperature due to the lubricant effect of cobalt oxides formed on the sliding surface. As a result, T800 coating was highly recommended as a durability improvement coating for the protection of sliding surface, such as high speed spindle.