Hydriding of Titanium.

The reason for undertaking this work is that the US Navy would like to use titanium in a number of critical applications, where it would come in contact with sea water at elevated temperatures. Although the general reputation of titanium is that it is corrosion resistant in these environments, there is the possibility that it could pick up sufficient hydrogen from this environment to form a hydride and thus lose its mechanical integrity. Therefore, we must evaluate all conditions that could lead to hydriding and determine the effects of hydrides on mechanical properties. During the second year of work, the goals have been the following to determine the effect of solution activity and temperature, material composition and heat treatment on the electrochemical properties of titanium to determine the effect of these same variables on the corrosion potential of titanium galvanically coupled with other metals to determine the critical potential of hydride formation as a function of solution activity and temperature, applied strain, and surface conditions to measure the rate of hydrogen diffusion in titanium to propose a model to describe crack propagation in titanium in these environments. All of the above work has been completed and the results are contained in this document. The results that we have obtained show that grade 2 titanium is generally resistant to hydrogen embrittlement. However, grade 3, with its higher interstitial content and lower hydrogen solubility is quite susceptible to hydrogen embrittlement. The mechanism by which this embrittlement occurs is one in which microcracks, which are centered on hydrides, form ahead of the main crack tip. With increased deformation these microcracks link up to the main crack and cause propagation.