The surface of AISI 1045 steel specimens was modified via two duplex surface treatments of (i) titanium diffusion coating followed by plasma nitriding (Ti-PN) and (ii) plasma nitriding followed by titanium diffusion coating (PN-Ti).A comparative study on the microstructure and wear properties of the fabricated TiN coatings was conducted.A scanning electron microscope equipped with energy-dispersive X-ray spectroscopy,X-ray diffractometer (XRD),and pin-on-disk wear test was utilized to evaluate the microstructures,phases,and wear properties of the coatings.XRD patterns of duplex-treated specimens illustrated that the modified layer consisted of nitride and carbo-nitride phases such as TiN and TiC0.7N0.3.The results also showed that Ti-PN treatment led to a low friction coefficient and the lowest wear factors,as compared with the PN-Ti treatment.Oxidation and mild fatigue fracture wear were found to be the main wear mechanism of the Ti-PN coating.The wear mechanism in the PN-Ti specimen involved a higher oxidative wear regime followed by plastic deformation wear regimes.