Soft Matter Materials Branch (RXAS)
2941 Hobson Way
Wright-Patterson AFB, OH 45433
Sam is a member of CAMM. His research is focused on understanding the microstructural evolution and mechanical performance of microstructural gradients in the low solvus high refractory (LSHR) nickel base superalloy. The dual microstructure heat treatment (DMHT), developed by NASA, produces a microstructural gradient in turbine disks, with coarse grains in the rim and finer grains in the bore. The transition region consists of a distribution of grain and γ′ sizes. Since superalloys typically have overlapping strengthening mechanisms, it is critically important to understand how extended periods of aging will affect the microstructural morphology and mechanical properties.
In his research, Samuel uses high resolution scanning electron microscopy (HR-SEM) and energy filtered transmission electron microscopy (EFTEM) to characterize the size and distributions of γ′ in the transition region of the disk. In addition to the high resolution microscopy of γ′, he uses electron backscattered diffraction (EBSD) to determine the distribution of grain sizes and amount of misorientation existing at the grain boundaries. Current investigations remain focused on extracting tensile specimens from the transition region and aging them in various conditions. Tensile specimens are mechanically tested on an electrothermal mechanical tester (ETMT), which is located at CAMM. Optical digital image correlation (DIC) is used to track the localization of strain during mechanical testing at room and high temperatures (> 700°C). Focused ion beam (FIB) sectioning is performed to extract TEM samples from the regions of localized strain. Analysis of FIB samples is conducted using conventional (CTEM) and scanning transmission electron microscopy (STEM) to determine the nature of prevailing crystalline defects within the region of interest. The defect information used in conjunction with the local characterization of γ′ will be used to determine which features significantly contribute to damage accumulation in the sample.