Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen.

M Neikter,C De Andrade Schwerz,M Colliander,T Hansson,M.-L Antti,R Pederson,P Åkerfeldt

doi:10.3390/ma13061287

Abstract

Titanium-based alloys are susceptible to hydrogen embrittlement (HE), a phenomenon that deteriorates fatigue properties. Ti-6Al-4V is the most widely used titanium alloy and the effect of hydrogen embrittlement on fatigue crack growth (FCG) was investigated by carrying out crack propagation tests in air and high-pressure H2 environment. The FCG test in hydrogen environment resulted in a drastic increase in crack growth rate at a certain ΔK, with crack propagation rates up to 13 times higher than those observed in air. Possible reasons for such behavior were discussed in this paper. The relationship between FCG results in high-pressure H2 environment and microstructure was investigated by comparison with already published results of cast and forged Ti-6Al-4V. Coarser microstructure was found to be more sensitive to HE. Moreover, the electron beam melting (EBM) materials experienced a crack growth acceleration in-between that of cast and wrought Ti-6Al-4V.

Highlights

Oxygen and hydrogen are used as fuel for space rockets [1]
The layers were oriented perpendicular to the major axis of the cylinders i.e., the applied load during the fatigue crack growth (FCG) tests was perpendicular to the additive manufacturing (AM) built layers
The electron beam melting (EBM) Ti-6Al-4V material consisted of columnar prior β grains

Summary

Introduction

Hydrogen is combusted rapidly in an oxygen-rich environment and a high propelling force can be achieved, as the energy density for hydrogen is high (142 MJkg−1 ) [2]. Hydrogen is excellent for combustion it can cause hydrogen embrittlement (HE), which deteriorates the mechanical properties. HE occurs at or ahead of crack tips because at these locations tri-axial stresses are present [3]. These stresses render slightly expanded lattices, making it more energetically favorable for the hydrogen to diffuse to this location. Once at the crack tip the hydrogen causes degraded properties due to one or several HE mechanisms [4,5]

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Results

Discussion

Conclusion