Effect of process duration on the microstructures of fast multiple rotation rolling-induced nanocrystalline layer and its wear properties

A nano-structured surface layer was prepared on the top surface of commercially pure titanium by fast multiple rotation rolling(FMRR) technique for the first time. X-ray diffraction (XRD), field emission scanning electron microscopy(FE-SEM), transmission electron microscopy(TEM), optical microscopy(OM), as well as Vickers test and wear test were used to characterize the microstructural evolution and mechanical properties of the nano-structured layer. The results indicated that when the treatment lasts for 60 min, the average grain size reduces to as small as 50 nm, and high-density mechanical twining was observed in deformed grains. Moreover, the surface modification resulted in an approximately two-fold increase in microhardness of the nano-structured surface layer and remarkable enhancement in wear resistance. The hardness reached up to 280HV0.05, and friction coefficient declined from 1.1 to 0.6 at sliding velocity of ∼0.1 m/s. The obtained results revealed that mechanical twining took precedence in the plastic deformation, and twining and dislocation interaction were induced in the refined nano-structured layer on the surface by FMRR.