On the effect of hydrogen on the elastic moduli and acoustic loss behaviour of Ti-6Al-4V

S L Driver,N G Jones,H J Stone,D Rugg,M A Carpenter

doi:10.1080/14786435.2016.1198054

S L Driver, N G Jones + Show 3 more

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https://doi.org/10.1080/14786435.2016.1198054

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Abstract

The elastic moduli and acoustic loss behaviour of Ti-6Al-4V (wt.%) in the temperature range 5–298 K have been studied using Resonant Ultrasound Spectroscopy. A peak in the acoustic dissipation was observed at 160 K within the frequency range 250–1000 kHz. Analysis of the data acquired in this study, coupled with complementary data from the literature, showed that this was consistent with a Snoek-like relaxation process with an associated activation energy of 23 3 kJ mol. However, the loss peak was broader than would be expected for a Snoek-like relaxation, and the underlying process was shown to have a spread of relaxation times. It is suggested that this effect arises as a result of variations in the strain experienced by the phase due to different local microstructural constraint by the bounding secondary phase.

Highlights

Ti-6Al-4V (Ti-6-4) is the most widely used titanium alloy, finding extensive applications in the aerospace industry
The microstructure is dominated by the hcp α phase, accompanied by a smaller volume fraction of the bcc β phase
Low levels of hydrogen in titanium alloys have been implicated in poor cold dwell fatigue resistance [5,6]

Summary

Introduction

Ti-6Al-4V (wt%) (Ti-6-4) is the most widely used titanium alloy, finding extensive applications in the aerospace industry. As with other titanium alloys, aluminium preferentially partitions to the α phase, whilst vanadium stabilises the β phase. Low concentrations of interstitial elements are present, which can influence the phase equilibria and properties of the alloy [1]. Among such interstitials, oxygen is known to be a potent α phase stabiliser and provides significant strengthening [2]. Low levels of hydrogen in titanium alloys have been implicated in poor cold dwell fatigue resistance [5,6]. The role of hydrogen in stress corrosion cracking is highly significant, as local corrosion-induced hydrogen enrichment and migration to areas of high tensile stress facilitates crack extension [7]

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