SEM in-situ Fatigue Observation on Crack Initiation and Growth from Inclusion in P/M Rene95 Superalloy

A special designed experiment was conducted for observing crack initiation and growth in P/M Rene95 superalloy under tension-tension loading by self-made SEM in-situ fatigue loading stag. Several alumina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. The cracks can be formed by two mechanisms. Generally, the cracks nucleated at the interface between inclusion and matrix. Sometimes, cracks were also formed inside the inclusion. As the increase of cycles, some cracks at the interface between inclusion and matrix broadened and propagated along the direction about 45° to the loading axis. On the other hand, the cracks inside the inclusion propagated in the inclusion and towards matrix.