Effect of microstructures on the high temperature stress rupture behavior of GTD222 superalloy prepared by selective laser melting

Abstract

The microstructure is the fundamental factor determining the high-temperature stress rupture performance of selective laser melted (SLMed) GTD222 superalloy. This study comprehensively investigates the influence of microstructures on the stress rupture behavior of the SLMed GTD222 superalloy by designing different heat treatments. The results demonstrate that direct aging leads to microstructures with relatively finer grains and a combination of coarse and fine columnar grains, which exhibit exceptional stress rupture plasticity. The enhanced plasticity can be attributed to the ease of deformation in the finer grains. The solution-aging treatment can result in the formation of coarser grains and easy precipitation of γ’ phase and carbides at grain boundaries. A substantial proportion of coarse equiaxed grains was formed during the heat treatment and high temperature stress rupture, which has greater strain resistance and consequently significantly improves the stress rupture life. With the gradual increase in equiaxed grains, the stress rupture life demonstrates a progressive increment. The cracks initiation predominantly occurs at the molt pool boundaries in direct aged alloys, while the crack initiations primarily take place at carbide positions of grain boundaries in solution-aging alloy. The multiple microstructural deformation mechanisms were found during the stress rupture process, including dislocation slip, dislocation bypassing of γ’ phase, dislocation penetration into γ’ phase, as well as the formation of deformation twins.