AN INVESTIGATION OF THE FATIGUE AND FRACTURE-BEHAVIOR OF MN-CONTAINING GAMMA-TITANIUM ALUMINIDES

The fatigue and fracture mechanisms in Ti-48A1-xMn (x = 1.4 to 2.0 at. pct) gamma-based titanium aluminide alloys are elucidated. Unlike most gamma alloys, which fail predominantly by transgranular fracture at room temperature, fracture in ternary Ti-48Al-xMn alloys is shown to occur mainly by intergranular failure. The incidence of intergranular failure increased with increasing annealing duration and temperature. Intergranular fracture is shown to occur as a result of the segregation of Mn to equiaxed and interlamellar boundaries. Annealing either above or below the eutectoid temperature results in the precipitation of alpha(2) particles. The reduction in the strength and toughness of ternary Mn-containing alloys is attributed to the combined effects of segregation and alpha(2) precipitation. A micromechanics framework is presented for the assessment of twin toughening mechanisms under monotonic and cyclic loading.