The effects of Ultrasonic Nanocrystal Surface Modification (UNSM) on the gas nitriding of Ti6Al4V alloy has been investigated. The gas nitriding was performed at 700 and 800 °C. The microstructure after UNSM and gas nitriding was characterized using X-ray diffraction and scanning electron microscopy. Microstructural investigations revealed the formation of an approximately 10 μm thick severe plastic deformation (SPD) layer after UNSM treatment. After nitriding at 700 °C and 800 °C, a compound layer consisting of an approximately 0.2 μm and 1.9 μm thick nitride layer was observed in UNSM-treated Ti6Al4V alloy, which exhibits a nearly two-fold increase in nitride layer thickness as compared with the un-treated sample. This suggests that the nitrogen adsorption and the reaction capability are enhanced in the UNSM-treated Ti6Al4V alloy. This enhancement can be attributed to the high density dislocations and grain boundaries introduced by UNSM that serve as efficient diffusivity channels for interstitial gaseous atoms.

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