Uphill diffusion and progressive embrittlement: hydrogen in titanium

Abstract

Titanium and its alloys may experience a progressive embrittlement at room temperature leading to catastrophic failure. Such embrittlement is shown in the cases cited to be due to hydrogen migration and the accumulation of brittle titanium hydrides in the presence of a sharp alloy composition gradient near a weld fusion line. The governing equation for such migration is presented, as well as for the similar effect of stress and temperature gradients. The results from a computer simulation of this equation are shown to correlate well with the results of experiments and with service failures . Methods to avoid this form of embrittlement are presented. Observations of the hydride formation at the junction of a titanium alloy and pure titanium are shown to provide the data for calculating the diffusivity of hydrogen at room temperature. Embrittlement occurs at room temperature much sooner than would be expected from extrapolation to room temperature of published elevated temperature diffusivity data.