Jingjing Qing came to Georgia Southern from the Materials Research Center at Missouri University of Science and Technology. She is a metallurgist with expertise in cast iron solidification, ferrous metallography, and materials characterization using electron microscopies. An assistant professor in the Department of Manufacturing Engineering, Dr. Qing is married to and collaborates in her research with Mingzhi Xu, assistant professor in the Department of Mechanical Engineering at Georgia Southern. Together, they have established a Georgia Southern student chapter of the American Foundry Society (AFS) and a lab in the new Engineering and Research Building.
Even before making her way to Georgia Southern, Qing won research funding from several manufacturing companies such as Spirit Aerosystems, Caterpillar, Nucor Steel, North American Stainless Steel; and the Ductile Iron Society. She also published in high-impact journals and won two AFS Best Paper Awards. Qing and Xu continue to impress at Georgia Southern in their publications, external research funding – and in receiving the prestigious AFS Howard F. Taylor Award, to recognize the paper presented at the 2020 Metalcasting Congress that has the greatest long-range technical significance in the field of cast metals technology: Structure of Spheroidal Graphite Nuclei and Spheroidizing Mechanism of Graphite in Mg-Treated Ductile Iron.
In this research, funded by Ductile Iron Society, atom probe tomography (APT) with high sensitivity and spatial resolution was applied to study the elemental distributions in graphite to better understand spheroidization of graphite in the ductile irons. Compositional analysis was performed at the graphite/matrix interface and graphite/nuclei interface using APT and energy dispersive X-ray (EDX). Distributions of various alloying elements at interfaces were obtained. Compositional gradients were observed at both the graphite/liquid interface and the graphite/nuclei interface. The graphite/nuclei interface was shown to be semi-coherent/incoherent using the transmission electron microscopy, with a high density of crystallographic defects and high curvatures in the graphite basal planes growing off the nuclei. Intercalation of large nodulizing elements within and in between the graphite basal planes was proposed to account for the spherical morphology of the graphite in ductile irons.
Another study that received good recognition was on the solidification of ductile irons. Qing performed an interrupted solidification experiment to retain structures at various stages of ductile iron solidifications. Austenite engulfment of spheroidal graphite particles occurred after independent nucleation of the two phases. She used a scanning electron microscopy (SEM) equipped with EDX and Auto Feature Analysis (AFA) software to perform the statistical analysis on size, morphology and distribution of the graphite particles to advance the understanding of graphite growth kinetics. The spheroidal graphite particles were extracted, and their growth features revealed the staged growth mechanism of the spheroidal graphite particles in the ductile iron. Thin film specimens of ~100nm thick were extracted from the spheroidal graphite particles for internal structure examinations using the Transmission Electron Microscopy (TEM). Crystal structure of the graphite was characterized based on the diffraction patterns. The curvature accommodation models with various crystallographic defects in the spheroidal graphite particle were generated in this study.
Another recently funded research was to advance the theory of nucleation of spheroidal graphite in the ductile iron. Qing used high resolution TEM to study the elemental distribution, crystal structure, and interface coherency of complex nuclei made of different compounds in spheroidal graphite. The spheroidal graphite nuclei were differentiated as the complex compound was made of oxide, nitride and sulfide. Atomic resolution images at various interfaces clearly displayed the highly defective graphite crystal structures. Thermodynamic calculations were successfully applied to understand the formation sequence of the different compounds in the complex nuclei. Nanoparticles of complex chemistry as the transition products were observed, which may contribute to the curvature accommodation of the graphite basal planes. The instability of these transition compounds can explain the inoculation fade phenomenon during the cast iron productions.
In a project collaborated with Spirit AeroSystems, Qing studied the solid silver embrittlement of the Ti 6-2-4-2 alloy. Experiments were conducted to track the lifetime of Ti 6-2-4-2 specimens subjected to various levels of tensile load at different elevated service temperatures when silver was in contact with the specimens. Effects of the contact pressure between silver and Ti alloy was evaluated. Interannual fracture characteristics near the Ag contact area in the Ti alloy was revealed with the SEM, indicating decohesion of the grain boundaries. Microvoids observed in the area away from silver contact side on the fracture surface indicate ductile failure of the alloy. Silver was found on the fracture surface primarily due to the diffusion of silver along the grain boundary.
Qing is currently collaborating with Duramatic Products to optimize the Austenite tempering process for manufacturing lawn mower blades.
