Effect of surface recrystallization on high-temperature tensile properties of a directionally solidified DZ409 Ni-based superalloy

• At 650 °C, yield strength decreases almost linearly with increasing recrystallization (RX) fraction, while elongation drops significantly up to 4.9% RX fraction, then stabilizes. • At 950 °C, both yield strength and elongation decrease as RX fraction increases from 0% to 4.9%, indicating detrimental effect at high temperatures. • Fracture modes change with temperature: mixed transgranular/intergranular cleavage at 650 °C, and ductile/intergranular dimple fracture at 950 °C. • Failure is driven by transverse grain boundaries introduced during RX, which act as crack initiation sites and propagation paths, leading to premature failure.