Plastic deformation behavior of Ll_2 type intermetallic compound containing precipitate phase.

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Optimum alloy compositions and heat treatments to obtain fine dispersion of disordered -particles in an Li_2 ordered '-Ni_3(Al,Ti), and the morphology change of precipitates during ageing have been investigated in terms of transmission electron microscopy. The ' phase hardens appreciably by the fine precipitation of disordered . The initial shape of precipitates formed during ageing is spherical or round-cubic and grow into platelets as ageing proceeds. High resolution electron microscopy revealed that the precipitates are perfectly coherent with the matrix ' as long as the -precipitates are plates. The chemical compositions of the martrix and the precipitates have been determined by using EDS microanalysis in an analytical electron microscope.Morphology of dislocations in deformed '-Ni_3(Al,Ti) single crystals containing fine dispersions of disordered -particles has been investigated in terms of weak beam dark field transmission electron microscopy. Superlattice dislocations dissociat … More e into fourfold shockley partial disloca-tions in a uniform supersaturated solid solution of ' phase and in the matrix. At any stage of ageing, dislocations cut through the particles and the Orowan bypassing process dose not occur in this alloy system.Strengthening mechanisms in an ordered intermetallic compound contaning coherent precipitates of lower antiphase boundary energy than the matrix have been investigated on the basis of observation of the interaction between deformation induced dislocations and disordered precipitates in an Ll_2 ordered Ni_3(Al,Ti). Extra work necessary to pulll out the dislocations from the precipitate is dependent on the difference of antiphase boundary energy between the matrix and the precipitatem the size and volume fraction of precipitate.Strength of '-Ni_3(Al,Ti) Ll_2 ordered phase containing fine precipitates of disordered phase have been examined on basing upon the proposed model. The model can explain almost quantitatively the age hardening behaviour of ordered Ni_3(Al,Ti) phase. Less