Hydrogen absorption and hydride formation in pure titanium T40 (grade 2) and TA6V ELI (grade 23) under cathodic polarization in artificial seawater

Alexandre Poloni ,Thierry Millot,Aude Mathis,Juan Creus,Egle Conforto,C Berziou ,C Savall ,A Oudriss ,S Frappart ,X Feaugas

doi:10.1051/matecconf/202032109002

Abstract

Different kinetics of hydrogen absorption in T40 (grade 2) and TA6V ELI (grade 23) under cathodic polarization in artificial seawater have been highlighted. These polarizations were made by applying potentials from -0.8 to -1.8V/SCE in artificial seawater and NaCl solution. Four stages were identified and related in term of hydrogen ingress, hydrides formation and calcareous deposit growth. The formation of γ and δ-hydrides have been observed, localized and characterized using several techniques. On T40, hydrides form as a layer that increases the surface roughness and clusters form in the bulk after first moments of hydrogen absorption. Whereas in TA6V ELI, hydrogen is absorbed by β-phase leading to a volume expansion of this phase. Then after reaching the hydrogen solubility limit of β-phase, hydrides form on interfaces α/β or α/α and in α grains. For long durations, the hydrogen ingress is limited by the subsurface hydrides and the stabilized calcareous deposit. These different steps are time depend on processes which need to be tacked into account to improve knowledge of hydrogen embrittlement in titanium alloys.

Highlights

Titanium alloys are chosen for the manufacturing of components used in a marine environment
Hydrogen picking linearly rises with time until 30h a quasi-plateau is observed for both alloys at 250 wppm for grade 2 and 300 wppm for grade 23
For our charging durations, only cathodic polarizations of -1.6V/SCE and more negatives lead to a noticed hydrogen uptake

Summary

Introduction

Titanium alloys are chosen for the manufacturing of components used in a marine environment. These alloys efficiently protect themselves from any damage due to this aggressive environment by forming a stable passive film of titanium oxide TiO2. When they are used in multi-materials systems under cathodic protection, these conditions could favour the hydrogen evolution reaction (HER), which may lead to the material embrittlement by hydrides formation and/or solute/plasticity interactions [1, 2]. Characterise the hydrogen state is a key feature to understand the hydrogen embrittlement sensitivity of titanium alloys.

Results

Discussion

Conclusion