INSITU OBSERVATION OF GAMMA-]ALPHA TRANSFORMATION OF FE PARTICLES IN A CU FE ALLOY

Martensitic transformation of gamma-Fe particles embedded in a Cu matrix is examined by in situ deformation in a 200 kV electron microscope. The moment of martensitic transformation triggered by glide dislocations is recorded successfully by a video recording system. This observation provides clear evidence that once the martensitic transformation starts it completes spontaneously within 0.02 s after the initiation. A large number of dislocations are emitted explosively from the particle at the moment of transformation indicating that the phases change involves large shear displacements. Furthermore, it is found that a secondary slip has to contact the particle in addition to the primary one in order to trigger off the transformation.