- Post Doctoral Researcher, CEMAS
Soft Matter Materials Branch (RXAS)
2941 Hobson Way
Wright-Patterson AFB, OH 45433
Dr. Samuel Kuhr performs research on nickel and titanium alloys. His nickel superalloy research focuses 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, produced a microstructural gradient in turbine disks, with coarse grains in the rim and finer grains in the bore. 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. Gradient microstructures extracted from the hybrid disk are mechanically tested on an electrothermal mechanical tester (ETMT) located at CAMM. Optical digital image correlation (DIC) is used to track the strain localization during mechanical testing. Gamma prime morphologies are characterized using high resolution scanning electron microscopy (HR-SEM) imaging as well as SEM and transmission electron microscopy (TEM) based x-ray energy dispersive spectroscopy (XEDS) techniques. Nickel superalloy deformation is examined using focused ion beam (FIB) specimens. Analysis of FIB samples is conducted using conventional (CTEM) and aberration corrected high resolution scanning transmission electron microscopy (HR-STEM) to determine the nature of prevailing crystalline defects.
Dr. Kuhr’s titanium research focuses on the characterization and simulation of translational friction welding (TFW) of Ti-17 (Ti-5Al-2Sn-2Zr-4Cr-4Mo) and Ti-6Al-4V alloys. TFW processes provide a unique ability to assemble quickly complex aerospace components. However, TFW thermo-mechanical processing produces local compositional variations in addition to a strain gradient. It is essential to understand the sequence of phase transformations that occur during welding to aid process models aimed at improving mechanical properties and overall life prediction. In his current research, TFW microstructures are simulated in a GleebleTM3500 thermo-mechanical tester. Specimens are examined with SEM and TEM techniques which included electron back-scattered diffraction (EBSD), back-scattered electron imaging (BSE) and XEDS, HR-STEM as well as transmission kikuchi diffraction (TKD). Through these methods, any local compositional and structural fluctuations are observed.