The room temperature tensile properties of age-hardened titanium-aluminum alloys in the concentration range from 14.5 to 18.1 at.% aluminum were correlated to the size and dispersion of the precipitated Ti3Al particles and to the interaction of moving dislocations with the particles. It was found that when the coherent, ordered Ti3Al particles were sheared by the moving dislocations the alloys were extremely brittle. As a result of the operative cutting mechanism large dislocation pile-ups were formed, causing premature failure. It was observed that the large dislocation pile-ups were able to fracture the grain boundaries. By controlled aging the particle size and interparticle distance were changed so as to exceed the critical value for inducing a dislocation by-pass mechanism. Dislocation loops were created around the particles by the moving dislocations and the formation of high stress concentrations due to pile-ups of dislocations was avoided. Thus, the plastic elongation to fracture of the brittle alloys was increased up to about 7 per cent without a decline of the high flow stress. © 1970.
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