Deformation twinning induced by micropores in TMS-75 superalloy

Thermomechanical cycling was performed in single crystal superalloy TMS-75 to investigate the detailed microstructural evolution. An interesting phenomenon shows that the area around the micropores tends to create many deformation twins, while the area far from the micropores exhibits few deformation twins. To interpret this feature, finite element analysis of the stress field around micropores proceeded, which gives the results that the stress isoline near the micropores region appears the feature of the acetabuliform distribution and possesses the bigger stress value at 45° angle direction relative to the applied stress axis. In addition, theoretical calculations were further conduced in an effort to clarify the critical conditions for twinning in Ni based single crystal superalloys. The feature that a high density of deformation twins occurs in the area around the micropores in superalloy TMS-75 results from the stress concentration in the region around the micropores.