Investigating the possibility of replacing IN 738LC gas turbine blades with IN 718

Abstract

The possibility of replacing IN 738LC gas turbine blades with IN 718 is investigated in terms of their creep behavior at different working conditions. The latter superalloy is domestically produced and therefore there is a strong interest in using this alloy in manufacturing gas turbine blades. For this purpose, first the creep behavior and constitutive equation of IN 718 have been determined using experimental data. Test samples were machined from as-received bars and their physical and mechanical properties together with their creep behavior were examined. Constant load uni-axial creep tests were carried out at two constant temperatures of 660 and 675°C. Initial stresses range from 490 to 690 MPa that are below the yield stress at each temperature level. The test results verify the quality of the domestically produced superalloy and show that its characteristics match with the international standards. In addition, numerical optimization techniques were used to obtain creep constitutive parameters of the produced alloy based on the experimental data. Then, the creep behavior of gas turbine blades, which operate at different rotating speeds, was investigated using finite element method. The results show that since the creep deformation of IN 718 is high, it can only be used in low and medium power gas turbines.