Directionally solidified superalloy DZ125L was tensile tested along the <001> direction. The strain rate sensitivity on tensile deformation behavior was studied. It is demonstrated that ultimate tensile strength, yield strength and elongation increase with the increasing of strain rate. The increasing of strength is related with the increasing of dislocation density and the dislocation interaction with γ'. The elongation evolution with strain rate mainly depended on the competing mechanisms of crack propagation and alloy hardening. The fracture of the alloy was found initiated at the primary MC carbide. With deformation, the microcrack propagated in zig-zag mode along the slip lines. The propagation and link of the microcracks induced the quasi-cleavage feature of DZ125L alloy.
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