The effect of laser pulse frequency on the microstructure and morphology of duplex treated Ti-6Al-4V alloy

Titanium alloys find widespread applications in multiple industries owning to their remarkable combination of properties like high specific strengths and good corrosion resistance. Nevertheless, their use in wear resistance applications was limited due to their poor tribological properties. This characteristic is attributed to the low plastic shearing resistance and the low work hardening properties of the alloys. To combat this, several surface treatment procedures have been suggested and implemented in the past with variable successes. One of the promising methods for improving tribological characteristics of these alloys is duplex treatment. In the present study a duplex treatment of laser nitriding and TiN-PVD (physical vapor deposition) coating was employed on Ti-6Al-4V alloy with variable laser pulse frequencies. It was found that the laser affected zone expands in size at higher laser pulse frequency. For the sample treated at 2000 Hz, the laser affected zone expands over a thickness of approximately 50 μm. Additionally, it was found that the microstructure was mainly composed of dendrite and a needle-like structures underneath in all treated samples. Metallic α-Ti was found to exist as observed from the XRD results which was later confirmed by XPS analyses and this was attributed to the nature of the PVD process.