High temperature tensile behaviour of the Ni-base superalloy GTD-111

The Ni-based superalloy GTD-111 is employed in high power stationary gas turbines because of its high temperature strength and oxidation resistance. The temperature dependence of the tensile behaviour of GTD-111 has been studied by tensile tests with a constant strain rate of 10(-4) s(-1) over the temperature range of 25-900 degrees C. The results showed an abnormal variation in tensile properties with increasing temperature. The yield strength decreased slightly with temperatures up to about 650 degrees C and then increased between 650 and 750 degrees C. Above 750 degrees C, a rapid decrease in-the yield strength was found. The tensile strength showed a similar behaviour except for its maximum, which occurred at 650 degrees C. Elongation values fluctuated more with temperature than did tensile properties. Transmission electron microscopy (TEM) investigations have been performed on fractured specimens to evaluate the dominant mechanism of deformation at different temperatures. TEM observations confirmed that these behaviours were affected by the properties of the gamma' phase changes in the mechanism of deformation of GTD-111 at high temperatures.