Microstructural Stability of Directionally Solidified Eutectic NiAl-Mo Under Static and Thermal Cycling Conditions

ABSTRACTThe quasi-binary eutectic NiAl-9% Mo with faceted molybdenum fibers was subjected to both thermal annealing conditions and to annealing under thermal cycling conditions to determine the microstructural stability of this alloy. The static temperature tests were run at 0.85TM - 0.97TM in an argon gas atmosphere. The thermal cycling tests were performed between temperatures of 700°C and 1200°C by induction heating disk-shaped specimens in an argon gas atmosphere using time-temperature heating and cooling profiles to approximate potential engine applications. To quantify microstructural changes, the fiber size and size distribution and number of fibers per unit area were measured as a function of time at temperature. The overall results demonstrate that the directionally solidified eutectic NiAl-9Mo subjected to thermal fatigue conditions exhibits cell boundary coarsening and large shape changes, whereas the microstructure under static stress-free annealing is stable.