Effects of post-processing on microstructure and mechanical properties of additively manufactured GH3230 superalloy

【Objective】 This study aims to address the critical issue of microcrack formation during the selective laser melting (SLM) of GH3230 superalloy. The primary objective is to optimize the SLM process parameters and systematically investigate the synergistic effects of hot isostatic pressing (HIP) and subsequent heat treatment (HT) on the microstructure evolution and mechanical properties of the alloy, thereby providing a feasible processing strategy for the high-quality SLM formation of GH3230 superalloy.
【Method】 Spherical GH3230 superalloy powder prepared via the high-speed plasma rotating electrode process (SS-PREP) was used as the raw material. The SLM process was conducted by adjusting the laser power to screen the optimal parameters with minimal microcracks. Three groups of samples were prepared: as-SLM, HIP-treated, and HIP+HT-treated. The microstructures were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The mechanical properties were evaluated by tensile tests at both room and high temperatures, and the fracture mechanisms were analyzed via fractography.
【Result】 Low laser power results in insufficient energy density and subsequent lack-of-fusion defects, while the parameter of 205 W effectively reduces microcracks and eliminates unmolten defects. After HIP treatment, all microcracks in the as-SLM state are fully closed. Chain-like carbides are precipitated continuously along both grain boundaries and intragranular regions, with an average size of 1.31 μm and an equivalent grain diameter of 7.14 μm. Following HIP+HT treatment, the carbides underwent remelting and redistribution, reducing their average size to 1.18 μm, while the grain size increases by 32.1% compared to the HIP state. This microstructural evolution lead to a decrease in room-temperature tensile strength due to the weakening of precipitate strengthening, but a synergistic enhancement in high-temperature tensile strength and plasticity is achieved via refined grain boundary carbides and grain coarsening. Fracture analysis reveals that the HIP+HT state exhibites quasi-cleavage fracture at room temperature and ductile fracture at high temperatures.
【Conclusion】 The 205 W laser power parameter effectively mitigates microcrack and lack-of-fusion defects in SLM-fabricated GH3230 superalloy. HIP treatment achieves full crack closure and uniform carbide precipitation, while HIP+HT further optimizes the microstructure by regulating carbide distribution and grain growth. The HIP+HT-treated alloy exhibits a balanced combination of reduced room-temperature strength and improved high-temperature mechanical properties, which is attributed to the cooperative effects of refined carbides and grain coarsening. These findings provide critical technical guidance for the industrial application of SLM-fabricated GH3230 superalloy in high-temperature service environments.