α-Phase transformation kinetics of U – 8 wt% Mo established by in situ neutron diffraction

Abstract

The α-phase transformation kinetics of as-cast U-8 wt% Mo below the eutectoid temperature have been established by in situ neutron diffraction. α-phase weight fraction data acquired utilizing Rietveld refinement at five different isothermal hold temperatures can be modeled accurately utilizing a simple Johnson-Mehl-Avrami-Kolmogorov impingement-based theory, and the results are validated by a corresponding evolution in the γ-phase lattice parameter during transformation that follows Vegard's law. Neutron diffraction data is used to produce a detailed Time-Temperature-Transformation diagram that improves upon inconsistencies in the current literature, exhibiting a minimum transformation start time of 40 minutes at temperatures between 500°C and 510°C. The transformation kinetics of U-8 wt% Mo can vary significantly from as-cast conditions after extensive heat treatments, due to homogenization of the typical dendritic microstructure which possesses non-negligible solute segregation.

Path length dependent neutron diffraction peak shifts observed during residual strain measurements in U–8 wt% Mo castings

“…This preliminary measurement was performed by placing a 3 Â 3 Â 3 mm cubic voxel along the central axis of the rod and acquiring data in 5 mm steps along its length, with the incident beam traveling parallel along the axis of the sample. Cast U-Mo alloys are subject to some degree of solute segregation during solidification , and the microstructure from a casting in the same production lot was reported by Steiner, Calhoun et al (2016). Despite AE1 wt% local segregation within dendrites on the 10 mm scale, the rods were confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to have a homogeneous average solute distribution along their lengths (7.95-7.98 wt%).…”

ANALYSES OF STRUCTURE PHASE STABILITY OF U-Mo TARGET OF THE NEUTRON SOURCE

“…Experimental data are taken from the paper [10] Elementary calculations witness that even under smallest inter-atom distance (3.4 Å in the alloy with 12% Мо, Fig. 3) in the center of octahedron, enough place is remained for free placement of molybdenum atom.…”

Event-based processing of neutron scattering data at the Spallation Neutron Source

“…Combining this chopping with the stroboscopic methodology, VULCAN provides the capability for fast real-time operando testing. Users have benefited from these scientific capabilities and conducted a broad range of new research in materials science and engineering, including stress-induced twin reorientation (Pramanick et al, 2011), phase transformation in shapememory alloys (Yang et al, 2017;Wang et al, 2017) and bulk metallic glass composites (Wu et al, 2017), transformationinduced plasticity in alloys (Yu et al, 2014;Huang et al, 2017), twinning/detwinning behaviors in metals (Wu et al, 2013(Wu et al, , 2014(Wu et al, , 2015Xie et al, 2017;Wu & An, 2016), residual stress relaxation in engineering structures (Aba-Perea et al, 2016), domain switching in oxides (Aman et al, 2014), non-equilibrium phase transformation during rapid heating (Yu et al, 2012), cycling and degradation of realistic-format batteries Wang et al, 2012;Liu et al, 2013Liu et al, , 2016, and in situ materials processing and synthesis (Cai, Liu et al, 2013;Chen et al, , 2014Steiner et al, 2016). Specific examples of the use of event data acquisition are chosen from battery charge-discharge, rapid heating of a dual-phase steel and cyclic fatigue-induced martensitic phase transformation.…”