Microstructure-Mechanical Property Relationships in High Temperature Ceramics
Transition Metal Carbides
Ceramics are often considered to be hard and brittle materials. Yet, certain classes of ceramics can exhibit significant ductility at elevated temperatures. Professor Thompson's research program studies particular classes of transition metal ceramics which exhibit this behavior. Particular concentration has been in the carbides and nitrides. In either class, modest changes in the metal:non-metal stoichiometry results in various microstructures ranging from equiaxed to acicular grains with secondary phases precipitating in a variety of morphologies. Such compositionally-driven microstructure formation provides tantalizing engineering opportunities to tailor thermo-mechanical properties, such as high temperature strength and creep. These microstructures are subjected to mechanical loading where upon the deformation mechanisms are quantified using dynamical electron diffraction techniques. Through in-group and collaborative interactions, first principle energy calculations are merged with experimental findings to understanding slip behavior.
A focus ion beam extracted TEM foil imaged using Scanning TEM-High Angle Annular Dark Field. The foil is from an interface region from a reaction couple between TaC-Ta powders. The various phases demonstrate possibilities for microstructural manipulation for tailored thermo-mechanical properties.
A Frank-Reed dislocation source emitting dislocations (red arrow) in a Ta2C specimen flexural tested near 2000 ºC
Highlighted Papers:
N. De Leon, X-X. Yu, H. Yu, C.R. Weinberger, and G.B. Thompson “Bonding effect on the slip difference in the B1 Monocarbides” Physical Review Letters 114 (2015) 165502
R.A. Morris, N. De Leon, and G.B. Thompson “Thermo-mechanical testing of tantalum carbides using a Lorentz-force, non-contact technique” Journal of the European Ceramic Society 33 (2013) 1639-1646
B. Wang, C. Weinberger and G.B. Thompson “A theoretical investigation of the slip systems ofTa2C” Acta Materialia 61 (2013) 3914-3922
N. De Leon, B. Wang, C. Weinberger, L. Matson, and G.B. Thompson “Elevated temperature deformation mechanisms in Ta2C: An experimental study” Acta Materialia 61 (2013) 3905-3913
R. A. Morris, B. Wang, L. Matson, and G.B. Thompson “Microstructural formations and phasw transformations pathways in hot isostatically pressed tantalum carbides” Acta Materialia, 60 (2012), 139-148
R.A. Morris, N. De Leon, and G.B. Thompson “Thermo-mechanical testing of tantalum carbides using a Lorentz-force, non-contact technique” Journal of the European Ceramic Society 33 (2013) 1639-1646
B. Wang, C. Weinberger and G.B. Thompson “A theoretical investigation of the slip systems ofTa2C” Acta Materialia 61 (2013) 3914-3922
N. De Leon, B. Wang, C. Weinberger, L. Matson, and G.B. Thompson “Elevated temperature deformation mechanisms in Ta2C: An experimental study” Acta Materialia 61 (2013) 3905-3913
R. A. Morris, B. Wang, L. Matson, and G.B. Thompson “Microstructural formations and phasw transformations pathways in hot isostatically pressed tantalum carbides” Acta Materialia, 60 (2012), 139-148
Laser Chemical Vapor Deposition of SiC
Laser-induced chemical vapor deposition (CVD) is a process in which material is deposited over a localized area directly from the vapor phase. With a moving and focused laser beam facilitating deposition, laser CVD can be used to additively form three-dimensional shapes like a rod/fiber or spring. Professor Thompson is interested in studying the effects of process parameters on the deposited material’s microstructure, phase, chemistry, and mechanical properties. The resulting deposition rates and fiber morphology can be linked by in situ measurements of temperature in the reaction zone by two color pyrometry.
SEM image of the SiC fiber and optical image of laser focal point on growing SiC fiber.