Unraveling compacted graphite evolution during solidification of cast iron using in-situ synchrotron X-ray tomography

DOI: 10.1016/j.carbon.2021.08.069

Authors: Chaoling Xu (Technical University of Denmark) , Tim Wigger (University College London; Research Complex at Harwell) , Mohammed Azeem (University College London; University of Leicester) , Tito Andriollo (Technical University of Denmark) , Søren Fæster (Technical University of Denmark) , Samuel Clark (University College London; Argonne National Laboratories) , Zhixuan Gong (University College London; Research Complex at Harwell) , Robert Atwood (Diamond Light Source) , Jean-Claude Grivel (Technical University of Denmark) , Jesper H. Hattel (Technical University of Denmark) , Peter D. Lee (University College London; Research Complex at Harwell) , Niels S. Tiedje (Technical University of Denmark)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Carbon , VOL 141

State: Published (Approved)
Published: September 2021
Diamond Proposal Number(s): 22627

Abstract: In spite of many years of research, the physical phenomena leading to the evolution of compacted graphite (CG) during solidification is still not fully understood. In particular, it is unknown how highly branched CG aggregates form and evolve in the semi-solid, and how local microstructural variations at micrometer length scale affect this growth process. We present here the first time-resolved synchrotron tomography combined with a bespoke high-temperature environmental cell that allows direct observation of the evolution of CG and relates this dynamic process to the local surrounding microstructures in a cast iron sample during repeated melting and solidification. Distinct processes are identified for the formation of CG involving the nucleation, growth, development of branches and interconnection of graphite particles, ultimately evolving into highly branched graphite aggregates with large sizes and low sphericities. CG is found to nucleate with a spheroidal or a plate-like shape, developing branches induced by high carbon concentration, e.g. thin melt channels. Additionally, CG grows much faster than spheroidal graphite during subsequent cooling in solid state. The direct visualization of the dynamic solidification process provides unprecedented new insights into formation mechanisms of CG and correlating factors such as local microstructural variations, and guides the development of CG iron solidification models.

Journal Keywords: cast iron; solidification; compacted graphite; X-ray tomography

Subject Areas: Materials, Engineering


Instruments: I12-JEEP: Joint Engineering, Environmental and Processing

Added On: 07/09/2021 09:30

Discipline Tags:

Engineering & Technology Materials Engineering & Processes Materials Science

Technical Tags:

Imaging Tomography