Microstructural and tribological characterisation of as sprayed and heat treated HVOF deposited Ni alloys

The microstructural, micromechanical (Vickers microindentation, scratch testing) and tribological (pin on disk tests against steel and alumina spherical pins) properties of three High velocity oxy-fuel (HVOF) sprayed Ni based alloy coatings, namely Diamalloy 4006 (Ni-20Cr-10W-9Mo-4Cu-1B-1C-1Fe), Tribaloy-700 (Ni-32Mo-16Cr-4Si-2Co) and Inconel-625 (Ni-22Cr-9Mo-4Nb), were characterised, both in the as sprayed condition and after thermal treatments at 600 degrees C and 800 degrees C. As deposited Tribaloy-700 possesses a low degree of crystallinity and lower hardness; crystalline intermetallics are formed after heat treatments, definitely improving mechanical strength and tribological resistance against 100Cr6 steel counterpart, but not against alumina counterpart. The Inconel-625 and Diamalloy 4006 as sprayed coatings consist of supersaturated crystalline solid solutions. The former is not much affected by heat treatments and has low hardness and poor tribological properties. The latter, instead, displays precipitation of secondary phases after heat treatment. Particularly, the 600 degrees C treatment improves coating strength and wear resistance against steel, whereas the 800 degrees C one is less effective, probably because excessive crystal grain size increase.