Title: Fatigue behaviour of Ti-6Al-4V alloy under combined low and high cycle and ultrasonic loading

Authors: In-Sik Cho; Jinil Park; Yongho Jeon

Addresses: Department of Hybrid Engineering, Sun Moon University, Kalson-ri, Tangjaong-myaon, Asan, 336-708, Korea ' Department of Mechanical Engineering, Ajou University, San 5, Woncheon-dong, Yeongtong-gu, Suwon, 443-749, Korea ' Department of Mechanical Engineering, Ajou University, San 5, Woncheon-dong, Yeongtong-gu, Suwon, 443-749, Korea

Abstract: The importance of the fatigue behaviour of Ti-6Al-4V alloys aerospace parts at low and high cycles has gained strength in last decades due to their long service life. In this study, an ultrasonic nanocrystalline surface modification (UNSM) treatment was performed on a Ti-6Al-4V alloy in order to extend the fatigue behaviour using a hydraulic and ultrasonic fatigue testing (UFT) systems. The fatigue enhancement mechanism of Ti-6Al-4V alloy was discussed on the residual stress and S-N behaviour with X-ray diffraction results. High-cycle fatigue behaviour of Ti-6Al-4V alloy was studied up to 10⁷-10⁹ using a piezoelectric ultrasonic fatigue tester operating at 20 kHz. The high-cycle fatigue results showed that the UNSM-treated specimen had better performances. Failure in the Ti-6Al-4V alloy was observed around the gigacycle regime with the fractures being found to initiate from the surface. The fracture surfaces exhibit brittle characteristics containing river patterns and cleavage facets, as well as striations.

Keywords: Ti-6Al-4V alloys; UNSM treatment; low cycle fatigue; high cycle fatigue; ultrasonic fatigue; aerospace components; titanium; aluminium; nanocrystalline surface modification; residual stress; brittle characteristics; river patterns; cleavage facets; striations.

DOI: 10.1504/IJMPT.2014.059031

International Journal of Materials and Product Technology, 2014 Vol.48 No.1/2/3/4, pp.18 - 33

Received: 18 Jan 2013
Accepted: 23 Aug 2013
Published online: 30 May 2014 *

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