LOW-CYCLE FATIGUE DAMAGE IN NICKEL-BASE SUPERALLOY SINGLE-CRYSTALS AT ELEVATED-TEMPERATURE

Low cycle fatigue tests on AM1 nickel-base superalloy single crystals were conducted under axial strain control at 650, 950 and 1100-degrees-C. The behaviour of the [001] orientation was investigated at the three temperatures, that of the [111], [101] and [213] specimens was studied at the two lower temperatures. The orientation dependence of fatigue life-total strain range curves was mainly due to variations in Young's modulus with orientation. Most cracks grow in stage II mode whatever the temperature. Cracks nucleate at micropores and in the interior of specimens at low temperatures; surface cracks induced by oxidation are dominant at high temperatures and low strain ranges. Most of fatigue life is spent in microcrack growth.