Phase transformation to the stable DO₂₄ structure in Ni-11.8 at.% Ti

The decomposition process and the deformation properties in compression tests of Ni-11.8 at.% Ti single crystals quenched from solid solution and aged within the metastable miscibility gap are investigated by conventional and high-resolution transmission electron microscopy. A mechanism based on superpartial dislocations is suggested for the phase transformation L1₂ - D0₂₄. A corresponding mechanism involving Shockley partial dislocations may be active for the transformation of the fee structure to the stacking sequence of the D0₂₄ structure. This transformation also provides a deformation mechanism which is likely to operate especially if concentration waves are present. Furthermore, defective stacking sequences derived from the D0₂₄ structure are suggested to be frequent. One of these defective sequences was identified by high-resolution electron microscopy in a D0₂₄ nucleus.