Microstructure, deformation and cracking characteristics of thermal spray ferrous coatings

The microstructure and local mechanical characteristics of thermal spray ferrous coatings have been determined. The emphasis has been on coatings made by the high velocity oxyfuel (HVOF) process, especially the role of Al alloy additives. The oxide phase present in the material and preferred pathways for local cracking and separation have been determined. Thin intersplat oxide layers emerge as preferential sites. These oxides are amorphous and the cracks extend along the oxide/α–Fe interfaces with low local fracture toughness, in the range 0.2–1 MPa√m. These low toughness pathways govern coating deterioration.