DESIGN, CREEP PERFORMANCE AND DEFORMATION BEHAVIOR OF AN ETA-PHASE STRENGTHENED NICKEL-BASE ALLOY FOR A-USC POWER PLANT APPLICATIONS

By utilizing computational thermodynamics in a Design of Experiments approach, it was possible to design and manufacture nickel-base superalloys that are strengthened by the eta phase (Ni3Ti), and that contain no gamma prime (Ni(3)AI,Ti). The compositions are similar to NIMONIC (R) 263, and should be cost-effective, and have more stable microstructures. By varying the aging temperature, the precipitates took on either cellular or Widmanstatten morphologies. The Widmanstatten-based microstructure is thermally stable at high temperatures, and was found to have superior ductility, so development efforts were focused on that microstructure. High temperature tensile test and creep test results indicated that the performance of the new alloys was competitive with NIMONIC 263. SEM and TEM microscopy were utilized to determine the deformation mechanisms during creep.