The Effect of Hot Corrosion on Creep and Low-Cycle Fatigue in the Cast Nickel-Base Superalloy IN738L

The creep and low cycle fatigue of IN738 have been studied as a function of environment.Creep tests were conducted in air, both with and without a deposited layer of 25% NaC1/75% Na2S04.In the presence of this deposited layer the steady state creep rate in air at 850°C and 275 to 375 MPa increased by about lOO%, while increases ranging from 90 to 170% were found at 307 MPa and 750 to 95O'C.The effect of the deposited layer and the stress and temperature dependence of the steady state creep rate was little, although its presence led to marked decreases in the rupture lives.The fatigue life determined in terms of cyclic plastic strain markedly decreased as the environment became more severe, in sequence from vacuum to air to NaCl+Na2S04 deposited layer.The large strain rate effect found in the air and hot corrosion envjtlfnments disappeared when the experiments were conducted in a vacuum of 1.3x10 Pa.