DETECTION AND CHARACTERIZATION OF THE HETEROGENEOUS DISTRIBUTION OF HYDROGEN IN TITANIUM COMPRESSOR BLADES BY NEUTRON COMPUTED-TOMOGRAPHY

The nondestructive evaluation of hydrogen in metals and alloys is a ma jor challenge with significant impact for the prevention of catastroph ic failure in critical engineering structures. Radiography using neutr ons has previously exploited the large neutron-hydrogen cross section to visualize corrosion products and moisture in metals; however, the m ethod is limited due to the effective averaging of the hydrogen densit y over the entire particle path length; thus, internal details may be hidden in thick components. We have developed a neutron tomographic im aging system specifically for the detection of hydrogen and utilized t he system to study component failures in jet aircraft engines. In seve ral recent accidents, failure of engine components, namely the titaniu m compressor blades have been implicated as contributing to the accide nts. Previous destructive methods of quantifying hydrogen in the blade s indicated hydrogen concentrations of approximately 500 ppm were pres ent and may have contributed to the unexpected failures. We used neutr on tomography to characterize the blades non-destructively and detecte d local hydrogen concentrations in the range of 1,000 to 7,000 ppm in spatially heterogenous distributions. Scanning electron microscopy, x- ray diffraction and mass spectrometry were utilized to validate the fi ndings. In addition, it was discovered that the hydrogen detected was not hydride as previously thought; but rather, interstitial or trapped hydrogen. These results demonstrate a significant role for neutron to mography in the detection of hydrogen in critical aircraft components and point toward applications in other areas where hydrogen embrittlem ent is known to be a major problem such as in the pipe systems of petr ochemical and nuclear plants.