CREEP BEHAVIOR MODELING OF UDIMET 720Li SUPERALLOY

Constant load creep tests on isothermally forged Udimet 720Li, an advanced superalloy for gas turbine disc application, were run in the stress/temperature field 900-450MPa/650-700℃ producing rupture times in the 20-5000h range.The creep curves have shown a predominant accelerating creep stage, that has been described by the following equation:ε=εmin (σ,T) 1 +C(σ)ε ] where εmin depends on stress and temperature, while parameter C depends mainly on stress.A strain dependent damage, defined by the parameter C, causes the accelerating creep stage at stresses lower than 750MPa, whilst its contribution to the creep strain acceleration is less important at higher stresses.The model rationalizes the different behaviors at high and low stress and has been validated with variable stress and temperature creep behavior.