Improved Tribaloy 800 HVOF Coating for Fretting Wear Resistance in Gas Turbine Hardware

The present study emphasis on the effect of heat treatment on thermally sprayed Tribaloy-800 high oxide coating. The work also focuses on the fretting wear resistance of self-mated coatings with and without heat treatment. Tribaloy T-800 coating was deposited using JetKote gun having coating composition of 28.5% Mo, 17.5%Cr, 3.4% Si and balance Co. Coating was done on Inconel X-750 substrate with thickness of approximately 250 μm. In the initial study, the assprayed coating shows low volume fraction of the Laves phase and low hardness 470VHN). Heat treatment was carried out at 680C for 4hrs under furnace cooling. Further, coating microstructure was evaluated in the as-sprayed and heat treated conditions using SEM and phase analysis was conducted by XRD. Heat-treatment of the Tribaloy-800 coating led to precipitation of submicrometric crystalline intermetallics and marginally improved hardness (630VHN). The micro indentation technique was applied to measure the variation of the coating hardness. High temperature fretting wear test were performed on both as received and heat treated specimens in order to understand the wear performance. The heat treated T-800 coating revealed increased wear resistance supporting improved microstructural features in the coating system. The analysis of coated surfaces showed that there was a transition from an adhesive-oxidational mechanism to a more severe plastic deformation and crack formation wear process.

Key Words: Tribaloy T-800, high-velocity oxyfuel spraying (HVOF), Heat treatment, scanning electron microscope, SEM, X-ray diffraction, XRD, Fretting wear