Manipulation of Grain Boundary Structures by Electric Fields

University Of California-Davis, Davis CA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: The application of an electrical bias during ceramic processing for manufacturing applications has the potential to dramatically improve processing times, lower required temperatures, and decrease required mechanical pressures. The mechanisms for these process improvements of these ceramics is unclear; this research is revealing the underlying reasons. The experimental work in this study is complemented by theoretical modeling. The anticipated results of this study are informing how electric fields can be utilized for enhancing processing conditions for existing materials, and tailoring of new functional ceramic materials. Graduate and undergraduate students are being trained in areas of materials science and engineering for subsequent careers in academia or fields of high-tech manufacturing. Participating university students are mentoring high school students from traditionally underrepresented communities to improve science literacy and college-going rates. TECHNICAL DETAILS: Electric field assisted sintering has demonstrated the feasibility to accelerate densification of powder compacts, lower processing temperatures, and suppress grain growth. The role of electric fields in the absence of current flow remains, however, mostly unknown. A major challenge is the systematic investigation of emerging defect structures in nanocrystalline ceramics due to the overwhelming number of randomly oriented general grain boundaries. Diffusion bonding of bicrystals in a custom-built setup is used to systematically investigate atomic and electronic grain boundary structures as a function of applied field strength, direction, and grain boundary geometry. This experimental approach allows the comparison of specifically selected grain boundary geometries as a function of the applied electric field, and elucidates whether externally applied electric fields impact on the thermodynamic stability of grain boundaries. Experiments are complemented by novel modelling routines that are based on variations of atomic density within the grain boundary cores. The combination of diffusion bonding, atomic resolution characterization, and theoretical modelling of the interfacial thermodynamic state is used to gain a quantitative mechanistic understanding of electric field effects on grain boundary formation. Field-assisted modifications of grain boundary networks are expected to become a disruptive technology for tailoring of new microstructures with unprecedented macroscopic physical properties. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.