Direct evidence for Suzuki segregation and Cottrell pinning in MP159 superalloy obtained by FEG(S)TEM/EDX Original Research Article

The effects of Suzuki segregation on the plastic flow behaviour of MP159 alloy deformed at high temperature and on the resulting dislocation structure have been examined. Elemental concentration profiles across both stacking faults and slip bands have been measured in a FEG TEM in nano-probe using the line scanning mode and EDX. It was found that Suzuki segregation resulted in continuously serrated plastic flow for deformation at temperatures from 450–670 °C and at a slow strain rate such as 1.0×10−4/s. TEM examination showed an increased dissociation width for dislocations and larger and more stacking faults after deformation at high temperatures as compared with those after deformation at room temperature. This can be interpreted as being due to the reduction of stacking fault energy by Suzuki segregation and/or Cottrell pinning. The elemental concentration profiles across stacking faults and slip bands showed that Mo and Al were more often found than other solutes to segregate to stacking faults and slip bands. Occasionally, the segregation of Ti and Nb could also be detected at stacking faults and slip bands.