Characterizing the thermal expansion of ultra-high temperature ceramics

There is a growing interest in understanding the performance and properties that make ultra-high temperature ceramics (UHTCs) promising for extreme environment applications, such as hypersonic platforms, nuclear reactors, and atmospheric re-entry. UHTCs are inorganic materials that exhibit metallic conductivity with melting temperatures above 3000 °C.

One such material, titanium diboride (TiB₂), has high strength in addition to its high melting point of ∼3225 °C, making it an important material for applications in armor and high durability coatings. While previous studies provide a strong basis for understanding the thermal-structural properties of TiB₂ up to 2040 °C, temperatures above this threshold have not been experimentally determined. However, this information is essential for the design of next generation UHTCs that will be operating well above this temperature limit in extreme environments and aerospace applications.

In a recent study led by materials scientist Elizabeth Sobalvarro, researchers performed in-situ, high-temperature, synchrotron x-ray diffraction (XRD) experiments on spherical TiB₂ beads at Argonne National Laboratory’s Advanced Photon Source. These sample beads were then levitated in a gas stream using a conical nozzle levitator system and heated with a laser to temperatures ranging from 25 to 3050 °C. This method of evaluation allows for a container-less material analysis that minimizes sample contamination. During levitation, XRD was used to characterize the effects of thermal expansion on the atomic structure of TiB_2. For example, expansion can lead to wear, cracking, and overall failure of a manufactured part, and the mitigation of these issues requires a full temperature-range understanding of this atomic scale (crystallographic) expansion.

The values determined in this experiment are in good agreement with previous studies at lower temperature ranges (below ∼2000 °C), showing the high fidelity of the experimental data (up to ∼3000 °C) collected in this study.

This work was supported by LLNL’s Laboratory Directed Research Development (LDRD) Program under project number 22-LW-021.

[E. Sobalvarro Converse, F. Thorpe, J. Rivera, H. Charalambous, G. King, J.T. Cahill, W.L. Du Frane, J.D. Kuntz, and S.J. McCormack, In-situ synchrotron x-ray diffraction and thermal expansion of TiB2 up to ∼3050 °C, Journal of the European Ceramic Society (2023), doi: 10.1016/j.jeurceramsoc.2023.01.050]