The role of intermetallic precipitates in Ti-62222S

Samples of Ti-62222-0.23wt.%Si were heat treated and aged at temperatures ranging from 1150°F to 1500°F with the view of effecting selective precipitation of α2 precipitates and silicides (i.e. TixZr5-xSi3). The effect of these intermetallic precipitates on the mechanical properties and fracture morphology was assessed via three separate microstructural conditions: Ti-62222S with α2 precipitates, Ti-62222S with α2 and silicide precipitates, and Ti-62222S with silicide precipitates. Both types of intermetallic precipitate appear to lower the fracture toughness, however α2 promotes intergranular fracture while silicides lead to transgranular failure and dimpling. The combined presence of the α2 and silicides leads to mixed mode failure. Further, since α2 is present in the α phase and silicides precipitate out in the β phase, it appears that the effect of each of these intermetallics in Ti-62222S is additive rather than synergistic.