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), werecharacterised, both in the as sprayed condition and after thermal treatments at 600uC and 800uC.As deposited Tribaloy-700 possesses a low degree of crystallinity and lower hardness; crystallineintermetallics are formed after heat treatments, definitely improving mechanical strength andtribological resistance against 100Cr6 steel counterpart, but not against alumina counterpart. TheInconel-625 and Diamalloy 4006 as sprayed coatings consist of supersaturated crystalline solidsolutions. The former is not much affected by heat treatments and has low hardness and poortribological properties. The latter, instead, displays precipitation of secondary phases after heattreatment. Particularly, the 600°C treatment improves coating strength and wear resistanceagainst steel, whereas the 800u°C one is less effective, probably because it causes excessivecrystal grain size increase.