Effects of the state of stress on the tensile and creep properties of γ-TiAl

Abstract

Tensile stress-strain tests at 20, 450 and 750 ° C and creep experiments at 750 ° C have been performed on plain and circumferentially notched bars of the candidate gas turbine blade material γ-titanium aluminide (γ-TiAl). Two notch shapes were examined to produce different stress states in the notch root region. In all cases notch strengthening was observed. Finite element calculations have also been carried out to determine the stress distributions developed in the notched bars during the tensile and creep tests. The tensile properties were represented by a Ramberg-Osgood relation with a range of strain-hardening exponents, m, and the creep behaviour by a Norton-type creep law with different stress indices, n. It has been found that a skeletal point exists in the notch cross-section where the stress state is independent of the values chosen for m and n. It is shown that the experimental results can be explained in terms of the state of stress developed at the skeletal point of each notch shape.