A study of hydrogen blistering mechanism for Molybdenum by Tritium radio-luminography

In order to study blistering mechanisms of Molybdenum (Mo), hydrogen distributions at and around blisters formed on Mo surfaces are examined by Tritium (T) radio-luminography or autoradiography (TARG). TARG shows that large amount of hydrogen (T) is accumulated at and near grain boundaries and some blisters are covered with Ag precipitates representing T under the blister skins. Two independent types of blistering mechanisms seem to occur on Mo surface simultaneously. One is typical blistering due to bubble coalescence accompanying plastic deformation of the blister skins and only very thin blister skins allow T detection by TARG. Another is exfoliation or cracking of a grain caused by mechanical fracturing of the grain boundaries and/or defect clusters due to brittle nature of Mo, remaining tritium on the fractured surface.