| dc.description.abstract | This study investigates the influence of sintering conditions and two different solid solution treatments (1020℃, 940℃) followed by aging treatment (two-stage: 720°C8h→620°C8h) on the microstructure and mechanical properties of porous IN 718 nickel-based superalloy. The examinations include optical microscopy (OM), scanning electron microscopy (SEM), and mechanical tests (hardness, compression).
The results demonstrate that in the sintered state, trace amounts of NbC carbides can be observed at grain boundaries. The microstructure consists of a γ matrix and precipitates of NbC carbides. The corresponding hardness, compression plateau stress, and energy absorption value are 219Hv, 370MPa, and 63J/g, respectively.
Following the high-temperature (1020℃) solid solution treatment, the microstructure is composed of a γ matrix and precipitates of NbC carbides. The hardness, compression plateau stress, and energy absorption value are reduced to 189Hv, 200MPa, and 29J/g, respectively.
Subsequent aging treatment results in the precipitation of strengthening phases, γ′ (Ni3(Al,Ti)) and γ＂ (Ni3(Nb)), leading to significant improvements in hardness, compression plateau stress, and energy absorption value, which reach 518Hv, 520MPa, and 64J/g, respectively. These values are substantially higher compared to the sintered state.
After the low-temperature (940℃) solid solution treatment, a significant amount of needle-like δ phase (Ni3(Nb)) is observed within the γ matrix. The microstructure consists of a γ matrix and δ phase (Ni3(Nb)). The corresponding hardness, compression plateau stress, and energy absorption value are 232Hv, 450MPa, and 66J/g, respectively.
The hardness increases by approximately 6% compared to the 1020℃ (high-temperature) solid solution treatment due to the precipitation of the δ phase (Ni3(Nb)), which reduces the degree of matrix supersaturation. However, this also leads to a decreased amount of γ＂ strengthening phase during aging treatment. Consequently, the hardness, plateau stress, and energy absorption after aging treatment are 434Hv, 460MPa, and 70J/g, respectively, which are lower than those of the 1020℃ (high-temperature) solid solution and aging alloy but still significantly higher than the sintered state. | en_US |