Transmission electron microscope investigation was performed on particle-dislocation interactions in Ni3Al-based intermetallics containing various types of fine precipitates. In an L12-ordered Ni3Al alloy with 4mol% of chromium and 0.2-0.5mol% of carbon, fine octahedral precipitates of N23C6 type carbide, which has a cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops were formed in Ni3Al containing fine dispersions of N23C6 particles. In the alloys with appropriate titanium content, fine precipitates of coherent disordered γ were formed during aging. The γ precipitates were initially spherical or rounded cubic in shape and grow into platelets as aging proceeds. Loss of coherency was initiated by the introduction of dislocations at the γ/γ′ interface and results in step formation at the dislocations. The γ precipitates become globular after the loss of coherency. In the γ′ phase hardened by the precipitation of the disordered γ phase, dislocations were attracted into the disordered γ phase and cut through the particles during deformation at any stage of aging. In Ni3Al containing a fine dispersion of disordered γ, super-dislocations were strongly attracted to the disordered particles and dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the matrix. It was shown by comparison that the strengthening due to attractive interaction was more effective than that due to repulsive interaction. The roles of the variation of the interaction modes and of the dissociation of super-dislocations in the matrix and particles were discussed in connection with the optimum microstructures of L12-ordered intermetallics as high temperature structural materials.

Dislocation-Particle Interaction in Precipitation Strengthened L12-Ordered Ni3Al. Chang, S.H.: Metals and Materials International, 2007, 13[1], 31-7