Restoring the tensile properties of PVD-TiN coated Al 7075-T6 using a post heat treatment

In this work, a post heat treatment cycle is proposed with the aim to recover the lost tensile properties of aluminium alloy 7075-T6 coated with a 3 μm thick titanium nitride (TiN) film by using a physical vapour deposition (PVD) process. First, it was found that the application of the PVD hot process with a high operating temperature of 450 °C significantly decreased the tensile properties of the coating-substrate system compared to those of Al 7075-T6. The yield and ultimate strength decreased by 78% and 54%, respectively. However, as a result of re-applying the T6 cycle (as the post heat treatment), substantial improvements of 243% and 77% were achieved in the yield and ultimate strength of the coated material, respectively. Fractography of the failed specimens indicated the TiN coating layer to be satisfactorily adhered to the substrate under tensile loading.

Research Highlights
► Tensile behaviour and properties of Al 7075-T6 coated with TiN using a PVD process.
► Detrimental effect of PVD high temperature on the tensile and hardness properties.
► Substantial restoration of the tensile properties using a post heat treatment (PHT).
► Excellent adhesion of TiN coatings to the aluminium substrate under tensile loading.