THERMAL-MECHANICAL FATIGUE OF TI-48AL-2V ALLOY LAND ITS COMPOSITE

Thermal-mechanical fatigue (TMF) and isothermal fatigue (IF) of a Ti-48Al-2V alloy and its composite, reinforced with TiB2 particles, were studied. In-phase TMF testing was conducted under the condition of a minimum temperature T-min = 100 degrees C and a maximum temperature T-max which ranged from 750 degrees C to 1400 degrees C. The applied cyclic stress ranges were 2.8 to 28 MPa and 4.2 to 42 MPa. The IF tests were carried out at a T-max. The TMF and IF lives are longer for lower T-max sind for smaller stress ranges in both the matrix alloy and its composite. The IF life at a given T-max is shorter than the TMF life in the matrix alloy at all temperatures employed and in the composite only at higher temperatures. At lower temperatures, the TMF and IF lives are essentially the same in the composite. The resistance to TMF is similar in the matrix alloy and the composite, but the IF resistance is greater in the composite than in the matrix alloy. The proposed TMF mechanism is nucleation and growth of voids on interlamellar plate, twin, and grain boundaries; their interlamellar, translamellar, and intergranular linkage; intergranular separation; and disintegration of lamellar structure.