Revealing Size Effects on Deformation Mechanisms in GH907 High-Temperature Alloy via In-Situ Tensile Testing

To investigate the effect of grain size on the deformation mechanism of superalloy GH907, specimens with varying grain sizes were prepared through solution treatment at different temperatures. Their mechanical properties and deformation behavior were systematically analyzed by combining in-situ tensile testing with microstructural characterization techniques (SEM, EBSD). The results indicated that as the solution temperature increased, the grain size increased from 8.52 μm to 34.96 μm, the yield strength decreased from 894 MPa to 210.03 MPa, and the ultimate tensile strength decreased from 1060 MPa to 543.3 MPa. The elongation reached its maximum value of 72% at 1020°C. Compared to the coarse-grained (31.07 μm) specimen, the fine-grained (9.18 μm) specimen exhibited an increase in yield strength and ultimate tensile strength of 330 MPa and 576 MPa, respectively, along with a more pronounced work-hardening effect, which conformed to the Hall-Petch relationship. In-situ tensile observations revealed that the activation of multiple slip systems, grain boundary bulging, and an increase in low-angle grain boundaries primarily characterized deformation in the fine-grained specimen. Significant interactions between twins and dislocations promoted coordinated grain rotation towards the <101> orientation. In contrast, deformation in the coarse-grained specimen was characterized by long-range transgranular slip, featuring concentrated slip bands and weak grain boundary accommodation, which easily induced local stress concentration. This study has revealed how grain size governs the deformation mechanisms in GH907 by modulating dislocation-grain boundary interactions and slip system activation, providing a theoretical basis for optimizing its mechanical properties.