An investigation on the fatigue behaviour of Al 7075-T6 coated with titanium nitride using physical vapour deposition process

This paper investigates the fatigue behaviour of aluminium alloy 7075-T6 coated with 3-μm-thick titanium nitride (TiN) coatings using a physical vapour deposition (PVD) process. Preliminary work demonstrated that the high operating temperature of the deposition process markedly reduced the tensile properties of the coating-substrate system by comparison to the uncoated Al 7075-T6. The low tensile properties of the coated material caused a considerable reduction in the load-carrying capacity under fatigue loading. Consequently, a substantial decrease of 90% was found in the fatigue life of the coated material. The lost tensile properties were then satisfactorily recovered by applying a post heat treatment to the coated alloy leading to significant fatigue life improvements to approach original properties of the uncoated Al 7075-T6. The evaluation of fatigue fracture surfaces at high magnifications indicated that the fatigue cracks initiated at the outer surface of the aluminium substrate under the coating thin layer.