Hydrogen Embrittlement of TiZrV Non-Evaporable Getter Coating

The study presented in this thesis work was performed to gain better understanding on the hydrogen saturation behavior of the TiZrV NEG coating, as well as on the effects of hydrogen sorption on the functionality of the coating. H$_2$ saturation experiments were conducted on two TiZrV coated stainless steel pipes subjected to two experimental conditions: instantaneous injections of H$_2$ at $1~$mbar injection pressure throughout 6 cycles, and continuous injection of H$_2$ at 5×$10^{-7}~$mbar to simulate saturation behavior at conditions similar to that of the H$_2$ injections part of the fixed target experiments at the LHCb experiment. The results demonstrated that at the injected hydrogen quantities, the sticking coefficient and the H$_2$ sorption rate of the TiZrV coating show a clear dependence on the absorbed hydrogen content, both decreasing at increased hydrogen absorption. The H$_2$ sorption limit was established as at minimum 0.407 H/TiZrV mol/mol at the 1 mbar injection condition and as 0.026 H/TiZrV mol/mol at the 5×$10^{-7}~$mbar continuous injection condition. Visual signs of embrittlement were not observed on the coating in the stainless steel pipes, proving the TiZrV alloy robust against hydrogen embrittlement. While embrittlement was not observed on the coating on the stainless steel pipes, the residual hydrogen content was observed to impose a limit on the H$_2$ sticking coefficient of the coating, highlighting the importance of ensuring sufficiently high hydrogen release kinetics and hydrogen removal rate during the reactivation. Besides, by characterization of witness samples from the $1~$mbar injection experimental condition it was determined that the repeated cycles of activation, H$_2$ injection, and venting decrease the efficiency of activation, motivating further investigation on the effect of hydrogen sorption on the activatability and the SEY of the NEG coating.