Notch strengthening in titanium aluminides under monotonic loading

An important concern for titanium aluminides is their limited ductility and its consequences for TiAl components containing stress concentrators. In recent experiments, evidence of notch strengthening has been found in one TiAl alloy under monotonic loading. The goal of this study is to fully explore this issue through tests on two cast alloys, one with a microstructure consisting of predominantly equiaxed gamma grains and the other having a fully lamellar microstructure. Tests involve monotonic tensile loading of notched specimens at room temperature under conditions of plane stress, where the notch radii are large relative to grain size. For each material, results from the testing of three notched specimen geometries are presented and finite element models are used to interpret the test results. This includes using the numerical models to apply Weibull statistical methods to predict notch strengthening in the specimens. It is shown that notch strengthening is clearly seen in both alloys tested and thus is likely to be a characteristic of TiAl alloys in general; however, strengthening is not as great as would be predicted by Weibull statistical methods as applied to brittle materials.