An electron microscopy study of modes of intermetallic precipitation in Ti-Cu alloys

The precipitation processes that accompany the aging of supersaturatedα-titanium solid solutions containing up to 6 wt pct Cu have been studied by thin foil electron microscopy and X-ray diffraction techniques. Two mechanisms of decomposition have been identified: i) the heterogeneous nucleation and growth of Ti₂Cu at interfaces and internal substructure such as dislocations, and ii) the uniform nucleation of thin, coherent, disk-shaped precipitates which lie on . The coherent precipitates can form with densities up to 10¹⁷ per cu cm; this and many morphological features of the precipitation process in Ti-Cu are analogous to the well-known behavior of Al-Cu alloys. The coherent precipitates first lose coherency along the edge of the disk and then along the flat faces. The mechanisms by which these two processes occur are considered in detail. Formerly Predoctoral Research Associate, University of Washington, Seattle, Wash.