Effect of building height on microstructure and mechanical property of GH4169 alloy fabricated by selective laser melting

Selective laser melting （SLM） technology can fabricate components with highly intricate geometries. Nevertheless， due to its layer-by-layer construction process，SLM inevitably leads to variations in microstructures and mechanical properties along the building direction，which in turn undermines the service stability of the fabricated components. Heat treatment is generally employed to enhance the homogeneity of microstructures and reduce the disparity in mechanical properties along the building direction. This study delves into the influence of building heights on the microstructures and mechanical properties of GH4169 alloy produced via SLM and sheds light on the mechanisms governing microstructure evolution during heat treatment. The key findings indicate that the microstructures of the as-built GH4169 alloy consist of the γ phase and Laves phase. The geometrically necessary dislocation density of the alloy demonstrates a decreasing trend as the building height increases， primarily attributable to the thermal cycles and heat accumulation that occur along the building height. After heat treatment， the recrystallization degree of the alloy at the bottom and middle sections reaches approximately 87.8%， while that at the top section is a mere 34.1%. This significant discrepancy in recrystallization is mainly due to the higher dislocation density at the bottom， which boosts the recrystallization driving force. The yield strength of the as-built GH4169 alloy at the bottom and middle sections is around 850 MPa， whereas that at the top section is approximately 780 MPa. Following heat treatment， the yield strengths of the alloy at different heights all approximate 1150 MPa. Owing to the variation in recrystallization， precipitation at the bottom is more pronounced than that at the top， resulting in a stronger precipitation strengthening effect. On the other hand， the finer grain size and higher dislocation density at the top contribute to enhanced grain boundary strengthening and dislocation strengthening. As a consequence， the strength of the alloy at the bottom and top sections after heat treatment is comparable.