Ultrasonic Nano-Crystal Surface Modification Assisted Gas Nitriding of Ti6Al4V Alloy

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.