ON THE TENSILE CREEP-BEHAVIOR OF A DIRECTIONALLY-SOLIDIFIED NI3AL-BASED ALLOY

High temperature tensile creep behaviour of a directionally-solidified Ni3Al-based alloy is presented. The study involved selection of nine alloy systems based on Ni3Al. The alloys contained varying amounts of Cr and Ta, fixed amounts of 1.5 at.% Hf and 0-5 at.% Zr and doped with 0.2 at.% each of C and B. The alloys were vacuum arc-melted into buttons and homogenized at 1050 C for 68 h. The test pieces of the alloys were hot compression tested at 600, 700, 800 and 900-degrees-C. The yield strength data of some of the alloys were superior to conventionally cast Mar-M 200, a cast nickel-base superalloy widely used in gas turbine structural applications. The best alloy system was chosen based on consistent performance in the hot compression studies. The alloy so chosen was directionally solidified and vacuum-homogenization-treated for 20 h at various selected temperatures. Optimum creep properties were observed at 1120-degrees-C, 20 h treatment. The minimum creep rate data of the DS alloy showed relatively higher values even at lower temperatures and stress levels as compared to Mar-M 200. Hence, the alloy is less promising in replacing nickel-based superalloys used as structural materials in gas turbine applications.