Tensile Behavior of the Second Generation Single Crystal Superalloy DD6

Tensile properties of the second generation single crystal superalloy DD6 were investigated from 20 °C to 1 100 °C. Microstructure evolution and fracture mechanism were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the tensile strength decreases slightly with increasing temperature from 20 °C to 400 °C. The tensile strength of the alloy increases with the increase of temperature from 400 °C to 800 °C. Above 800 °C, the yield strength of the alloy decreases greatly with increasing temperature. The elongation and contraction of area almost present opposite tendency in contrast to changes of the tensile strength. At lower and intermediate temperature (from 20 °C to 850 °C), the tensile fracture mechanism shows quasi-cleavage mode, while at high temperature (980 °C and 1 100 °C), it is dimple mode. The γ′ precipitate morphology still maintains cubic after tensile fracture at lower and intermediate temperature. The γ′ phase changes into rectangular solid at high temperature. The γ′ phase is sheared by anti-phase boundary (APB) or stacking faults at lower and intermediate temperature. At high temperature, dislocations overcome γ′ through by-passing mechanism.