MAE Seminar: Structure, Microstructure and Mechanical Properties of Transition Metal Carbides

Abstract: Ultra-High-Temperature Ceramics are a class of materials that have melting temperatures above 3000 C. These materials are used in applications where structural stability is of paramount importance. In this talk, we will focus on describing one class of these materials: the group IVB and VB transition metal carbides. In addition to exceptional melting temperatures, these materials have high hardness, and good thermal and electrical conductivity, all of which are dependent on carbon content. This provides the ability to vary the properties of the material and results in a wide range of observed mechanical properties. In addition, the slip characteristics of these materials are only partially documented as large-scale deformation only occurs above half of the melting temperature.

 

In this talk, we review some aspects of the mechanical properties of these materials including the role of carbon content and the role of the transition metal type in regulating deformation. We present some of our recent work in high-temperature 4-point bend tests and the identification of dislocation using traditional dynamical TEM analysis in TaC and HfC and Ta₂C.  We compare these results against literature observations as well as DFT calculations of stacking fault energies. Our computational results suggest why slip at low temperatures is observed to occur on the {111} planes in TaC and {110} planes in HfC, while slip occurs on the {0001} and {10-11} planes in Ta₂C.  We then present some of our DFT studies of the role of carbon vacancies on the mechanical properties to determine its role in hardening and contribution to plastic deformation.  Our results demonstrate that chemical bonding and microstructure work in concert to determine the mechanical properties of these materials.