Effect of substrate surface condition on fatigue behavior of cold sprayed Ti6Al4V coatings

- Cold sprayed Ti6Al4V coatings on ground Ti6Al4V substrates survived the longest fatigue life.
- Coatings on water-jet cut substrates survived the shortest fatigue life.
- Fatigue cracks initiated from interface and grew via micropores in coatings.
- Substrates with lower surface roughnesses led to higher adhesion strengths of coatings.

Ti6Al4V coatings were deposited on Ti6Al4V substrates by using a high pressure cold spray system. Before deposition, the substrate surfaces were prepared with four different surface preparation methods, namely, grinding, milling, sand blasting and water-jet cutting. The fatigue behavior of the coated specimens was studied with three point-bending-fatigue test. The fracture characteristics of the specimens were observed by using scanning electron microscopy. The surface roughness and its effect on the crack initiation and propagation in the coatings were also investigated. The results indicated that the fracture mode of the coated samples was interface cracking. At two different stress levels such as 420 and 360 MPa, the samples with the coatings deposited on the ground surfaces survived the longest fatigue life before failure, while the samples with the coatings deposited on the water-jet cut surfaces survived the shortest fatigue life. It was clearly shown that the fatigue strength of the cold sprayed Ti6Al4V coatings was strongly affected by the both spraying and substrate surface preparation conditions.