INFLUENCE OF GRAIN-SIZE AND HEAT-TREATMENT ON THE MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF THE NICKEL-BASE SUPERALLOY U-720 LI

The purpose of the current investigation was to develop an optimized b alance between creep resistance and LCF-strength of U 720 LI, a high-s trength nickel-base superalloy. While a fine grain size is beneficial for improved LCF-strength, it is detrimental to high-temperature creep resistance. Therefore, microstructures with medium grain sizes in the range of 50-150 mu m were produced by appropriate recrystallization t reatments. The coarse grain size showed improved creep resistance and lower yield stress as well as a tendency for lower LCF-strength. By in creasing the amount of fine gamma'-precipitates by modified aging trea tments, it was possible to increase the yield stress considerably with a concomitant increase in creep strength. (C) 1997 Elsevier Science S .A.