Precipitate strengthening of a γ′-(Ni,Co)3(Si,Ti)-intermetallic alloy

Homogeneously distributed, coherent precipitation of the disordered fcc γ-phase has been observed in an L12-long-range ordered γ′-intermetallic (Ni,Co)3(Si,Ti)-alloy with the composition Ni58Co20Si10Ti12. This leads to precipitate strengthening of the alloy after aging in the temperature range from 973 to 1073 K, as revealed by hardness measurements. In order to understand the strengthening mechanism, in-situ tensile tests of thin foils of the aged alloys were carried out in a transmission electron microscope. The motion of the superdislocations in the γ′-matrix and their interaction with the disordered γ-precipitates were analyzed. It was found that most of the 〈110〉 superdislocations were of screw character. They were dissociated dominantly into two unit 1/2〈110〉 dislocations separated by an antiphase boundary (APB) on the {111} slip planes. Their movement was jerky. They were strongly pinned by the γ-precipitates due to the absence of the APB in the disordered γ-phase. The pinned configurations of the superdislocations have been simulated in a computer.