Measurement of grain boundary strength of Inconel X-750 superalloy using in-situ micro-tensile testing techniques in FIB/SEM system

Grain boundaries (GBs), known as two-dimensional defects, are omnipresent in polycrystalline metallic alloys and thus influence a wide range of mechanical properties under different environmental conditions like irradiation and corrosion. Therefore, quantifying the strength of individual GBs is critical for understanding the degradation of mechanical properties of materials under different conditions. In this study we developed an efficient approach for the fabrication of micro-tensile specimens with a GB almost perpendicular to the tensile direction, which is expected to advance the development of individual GB tensile testing at micro or nanoscale in a wide scope of materials. An in-situ cantilever micro-tensile testing method was developed and used to quantify the strength of a n-ary sumation 3 GB in Inconel X-750 with the combination of finite element modeling. The average ultimate tensile strength (UTS) of a non-irradiated n-ary sumation 3 GB is estimated at around 1.4 GPa, comparable to that of a neutron-irradiated n-ary sumation 3 GB with a dose of ~1.5 dpa (1.3 GPa). Moreover, the in-situ push-to-pull micro-tensile testing technique developed in this work provides valuable insights into the high-angle GB deformation and fracture behavior. This method generates qualitatively similar ductility behavior before and after neutron irradiation as the bulk material testing. However, the ductility and UTS values obtained from this method are different from bulk measurements due to vastly different specimen dimensions.

Automated summary

Grain boundaries, as two-dimensional defects, play a significant role in the mechanical properties of polycrystalline metallic alloys. This study developed a method to fabricate micro-tensile specimens for quantifying the strength of individual grain boundaries. The results showed that the tensile strength of non-irradiated grain boundaries was estimated to be around 1.4 GPa, comparable to that of irradiated grain boundaries. Additionally, valuable insights into high-angle grain boundary deformation and fracture behavior were obtained.