Thermomechanical process optimization of U-10wt% Mo – Part 2: The effect of homogenization on the mechanical properties and microstructure

Abstract

Please cite this article as: ABSTRACTIn the first part of this series, it was determined that the as-cast U-10Mo had a dendritic microstructure with chemical inhomogeneity and underwent eutectoid transformation during hot compression testing. In the present (second) part of the work, the as-cast samples were heat treated at several temperatures and times to homogenize the Mo content. Like the previous ascast material, the "homogenized" materials were then tested under compression between 500 and 800°C. The as-cast samples and those treated at 800°C for 24 hours had grain sizes of 25-30 µm, whereas those treated at 1000°C for 16 hours had grain sizes around 250 µm before testing.Upon compression testing, it was determined that the heat treatment had effects on the mechanical properties and the precipitation of the lamellar phase at sub-eutectoid temperatures.

Modeling the homogenization kinetics of as-cast U-10wt% Mo alloys

“…This technique will only be valid if EDS line scans are drawn on the given sample condition of U-10Mo. This technique is an extension of Snyder's work [6] and attempts to incorporate the overall microstructure to predict the homogenization kinetics.…”

“…In order to fabricate U-10Mo monolithic plates consistently, at a lower cost and with high yield, a thorough understanding of the microstructure evolution kinetics from as-cast to the final formed structure after various material processes is required. The U-10Mo as-cast microstructure is an inhomogeneous dendritic structure with molybdenum-rich and -lean regions [4][5][6][7]. It has been observed in U-10Mo that, depending on the casting process adopted [5],microstructures with different grain size, molybdenum inhomogeneity,secondary dendrite arm spacing and carbide distribution wereobserved.…”

“…Based on the earlier work [1][2][3][4][5][6][7] on the thermomechanical processing of U-10Mo it was determinedthat different combinations and sequences of material processes may result in a variety of microstructures with different Mo segregation, grain morphology, phase volume fractions, carbide inclusions, and so on. In order to fabricate U-10Mo monolithic plates consistently, at a lower cost and with high yield, a thorough understanding of the microstructure evolution kinetics from as-cast to the final formed structure after various material processes is required.…”

“…The kinetics of the homogenization is dependent on the grain size and the other aforementioned parameters, and experimentally determining the time and temperature to homogenize is time-consuming and labor-intensive. Recent work on homogenization of U-10Mo was performed by Leenaers [7] and Joshi et.al [4][5][6]. The homogeneity or inhomogeneity was observed using the x-ray techniques in scanning electron microscope (SEM).…”

“…These models used scanning electron microscope (SEM) energy dispersive spectroscopy (EDS) line scans and microhardness measurements to determine the degree of inhomogeneity. A simple analytical model [13]was used by Snyder [6] to determine the time required to homogenize the entire casting. Despite the ease of using this model, that work does not take into account the variability associated with the entire microstructure or is localized to the regions where the line scans are taken and the step size of the scans.…”