RETRACTED ARTICLE: Dislocation-particle interaction in precipitation strengthened Ll₂-ordered Ni₃Al

Abstract

Transmission electron microscope investigation has been performed on the particle-dislocation interactions in Ni₃Al-based intermetallics containing various types of fine precipitates. In an Ll₂-ordered Ni₃Al alloy with 4 mol.% of chromium and 0.2–0.5 mol.% of carbon, fine octahedral precipitates of M₂₃C₆ type carbide, which has a cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are formed in Ni₃Al containing fine dispersions of M₂₃C₆ particles. In the alloys with appropriate titanium content, fine precipitates of coherent disordered γ are formed during aging. The γ precipitates are initially spherical or rounded cubic in shape and grow into platelets as aging proceeds. Loss of coherency is 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 are 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, superdislocations are 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 is shown by comparison that the strengthening due to attractive interaction is more effective than that due to repulsive interaction. The roles of the variation of the interaction modes and of the dissociation of superdislocations in the matrix and particles are discussed in connection with the optimum microstructures of Ll₂-ordered intermetallics as high temperature structural materials.