The paper experimentally investigated the change of LF9 properties, including strength at room temperature and 350°C, plasticity and impact toughness, under various heat treatment schedules. Results show that the strength of LF9 decreases and plasticity and toughness increase after secondary aging, with the increase of solid solution temperature. Meanwhile, with the increase of aging time, the strength of LF9 increase and plasticity and toughness decrease. The investigation of optical metallography, TEM and phase analysis indicate that the phenomena are mainly caused by the precipitation of η, γ’and γ’’.

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