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 mos t gamma alloys, which fail predominantly by transgranular fracture at room temperature, fracture in ternary Ti-48Al-xMn alloys is shown to o ccur mainly by intergranular failure. The incidence of intergranular f ailure increased with increasing annealing duration and temperature. I ntergranular fracture is shown to occur as a result of the segregation of Mn to equiaxed and interlamellar boundaries. Annealing either abov e or below the eutectoid temperature results in the precipitation of a lpha(2) particles. The reduction in the strength and toughness of tern ary Mn-containing alloys is attributed to the combined effects of segr egation and alpha(2) precipitation. A micromechanics framework is pres ented for the assessment of twin toughening mechanisms under monotonic and cyclic loading.