THE ROLE OF INTERMETALLIC PRECIPITATES IN TI-62222S

Samples of Ti-62222-0.23wt.%Si were heat treated and aged at temperatu res ranging from 1150 degrees F to 1500 degrees F with the view of eff ecting selective precipitation of alpha(2) precipitates and silicides (i.e. TixZr5-xSi3). The effect of these intermetallic precipitates on the mechanical properties and fracture morphology was assessed via thr ee separate microstructural conditions: Ti-62222S with alpha(2) precip itates, Ti-62222S with alpha(2) and silicide precipitates, and Ti-6222 2S with silicide precipitates. Both types of intermetallic precipitate appear to lower the fracture toughness, however alpha(2) promotes int ergranular fracture while silicides lead to transgranular failure and dimpling. The combined presence of the alpha(2) and silicides leads to mixed mode failure. Further, since alpha(2) is present in the alpha p hase and silicides precipitate out in the beta phase, it appears that the effect of each of these intermetallics in Ti-62222S is additive ra ther than synergistic.