Effect of ultrasonic nanocrystalline surface modification on the water droplet erosion performance of Ti-6Al-4V

The effect of ultrasonic nanocrystalline surface modification (UNSM) on the water droplet erosion (WDE) performance of Ti-6Al-4V was studied. It was observed that UNSM induces deep levels of compressive residual stresses in both the scanning and transverse directions. The treated surface revealed microdimples in a micro tracked fashion. Mechanical deformation marks were observed within the grains due to excessive plastic deformation and variation in grain size was observed across the ultrasonically modified layer. Microhardness of the UNSM condition was enhanced significantly as compared with the untreated (As-M) condition. The WDE performance tests for the UNSM and As-M conditions were conducted in a rotating disc rig in accordance with ASTM G73 standard. Influence of impact speed on WDE was explored on two different sample geometries (T-shaped flat and airfoil). WDE results showed that the flat UNSM samples had enhanced WDE performance at speeds 250, 275 and 300 m/s as compared with the As-M condition. At 350 m/s, both UNSM and As-M conditions showed similar performance. UNSM airfoil samples showed mild enhancement in the WDE performance at 300 m/s during the advanced stage as compared with the As-M condition. At 350 m/s, the UNSM airfoils do not show enhancement in WDE performance. (C) 2016 Elsevier B.V. All rights reserved.