抄録
Hydrogen behavior in fatigue crack growth of lamellar TiAl intermetallic compounds has been studied by means of hydrogen microprint technique. We can visualize the hydrogen in metal using the silver reduced by the hydrogen. Hydrogen was introduced to specimens by cathodic charging technique, and then metal-hydride on the charged specimen surface were removed by electropolishing. For the hydrogen microprint technique, specimen surface was covered with collodion and photographic emulsion before pre-cracking. Fatigue crack growth tests were performed by using the hydro-servo testing machine in a darkroom. The relationship between the stress intensity factor range and crack growth rate was studied, and region of reduced silver particles was detected for all test conditions. The fatigue crack growth was accelerated with hydrogen-charged specimens as compared with non-charged specimens. In parallel type specimens, in which cyclic load was applied perpendicular to the lamellar boundaries, the main crack grew along lamellar boundaries and large amount of silver precipitates was observed in charged specimens. It was deduced that hydrogen reduced the strength of lamellar boundaries. In perpendicular type charged specimens, in which cyclic load was applied parallel to the lamellar boundaries, it was observed that silver precipitates accumulated on the slip lines and the main crack grew partially along the slip lines. Based on the observation, it was deduced that the hydrogen promoted slip and reduced the strength of slip plane.
