Tribological behavior of cold sprayed Inconel 718 coatings at room and elevated temperatures

In this study, Inconel 718 coatings were fabricated by high pressure cold spray deposition and the microstructure and tribological properties of the coatings were systematically investigated at both room and elevated temperatures. At the first place, the investigation on the effect of thermal exposure on the surface oxidation of the coatings was conducted in the absence of sliding. It was found that oxides started to form on the coating surface when the ambient temperature was above 500 degrees C. At 600 degrees C, a NiFe2O4 spinel oxide layer spread over the coating surface. Under sliding against an Al2O3 counter ball, oxides started to form on the coating surfaces in contact with the ball when the ambient temperature was above 200 degrees C due to the fact that the frictional and external heat had facilitated the formation of the oxides. Thus, the friction coefficients of the Inconel 718 coatings decreased with the increase of ambient temperatures. However, the wear rates of the coatings increased at 100 degrees C and 200 degrees C compared to those of the coatings tested at room temperature, which was due to the decrease of hardness and severe abrasive wear. When the ambient temperature was further increased to 300 degrees C, a transition in wear mechanism occurred and the wear rates decreased due to the formation and breakage of the surface oxides that could act as lubricants between the counter ball and coating. With further increase of ambient temperature, a 'glaze' layer was formed and grew on the wear tracks, which could act as a protective layer and showed a load-bearing effect that prevented further removal of the coating materials, resulting in an improved wear resistance of the Inconel 718 coatings at elevated temperatures. Therefore, cold sprayed Inconel 718 coatings could be potentially used under wear conditions at elevated temperatures.