Surface nanocrystallization by ultrasonic nano-crystal surface modification and its effect on gas nitriding of Ti6A14V alloy

The effects of Ultrasonic Nanocrystal Surface Modification (UNSM) on the gas nitriding behavior of Ti6A14V alloy have been investigated. Gas nitriding was performed at 700 and 800 degrees C. The microstructure after UNSM and gas nitriding was characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Microstructural investigations revealed the formation of an approximately 10 mu m thick severe plastic deformation layer as well as nano-grains after UNSM treatment. The UNSM-treated Ti6A14V alloy formed 0.26 mu m and 1.35 mu m thick nitride layers after nitriding at 700 degrees C and 800 degrees C, respectively, and UNSM resulted in an increased layer thickness relative to untreated samples at both temperatures. The results suggest that nitrogen adsorption and reaction capability were enhanced in the UNSM-treated Ti6A14V alloy. This enhancement can be attributed to high-density dislocations and grain boundaries that were introduced by UNSM and served as efficient channels for nitrogen diffusion.