Intermediate temperature brittleness in a directionally solidified nickel based superalloy M4706

The variation of the tensile ductility of a directionally solidified nickel-based superalloy M4706 with temperature is investigated in the temperature range from room temperature to 980 degrees C. It is found that intermediate temperature brittleness occurs in M4706 at temperatures between 400 and 650 degrees C. Tensile tests on single crystal M4706 and in-situ nano-compression tests on the freestanding gamma' particles show that the intermediate temperature brittleness of the experimental alloy is not associated with the grain boundary and the deformation capacity of gamma' precipitates in the temperature range. Scanning electron microscope and transmission electron microscope observations disclose that the phenomenon is associated with the glide plane decohesion, which in turn corresponds to the frequent stacking fault shearing during tensile deformation.