Mechanical and Fatigue Characteristics of Ti-6Al-4V and Inconel 718 Alloys after Ultrasonic Nanocrystal Surface Modification (UNSM) Treatment

This study investigates influence of Ultrasonic Nanocrystal Surface Modification (UNSM), a novel surface treatment technology, on mechanical characteristics and rotary bending fatigue performance of Ti-6Al-4V and Inconel 718 alloys. Mechanical properties are acquired and compared for UNSM treated and untreated specimens. Cantilever type rotary bending fatigue tests were used to acquire and compare fatigue data for UNSM treated and untreated specimens of both alloy. Ti-6Al-4V specimens were subjected to fatigue tests with simultaneous exposure to corrosive environment via 3.5% NaCl solution. Fracture analysis is performed. UNSM is found beneficial to Ti-6Al-4V and Inconel 718 alloys fatigue indicated by improved S-N curves. The improvement in fatigue performance is attributed mainly to UNSM induced compressive residual stress, micro hardness and nano grain in the subsurface of the material. These are seen as factors contributing to retardation of crack initiation and propagation.