Thermal Conductivity Characterization of Hafnium Diboride‐Based Ultra‐High‐Temperature Ceramics

Abstract

We evaluated the thermal conductivity of HfB 2 -based ultra-hightemperature ceramics from laser flash diffusivity measurements in the 251-6001C temperature range. Commercially available powders were used to prepare HfB 2 composites containing 20 vol% SiC, some including TaSi 2 (5 vol%) and Ir (0.5 or 2 vol%) additions. Samples were consolidated via conventional hot pressing or spark plasma sintering. Processing differences were shown to lead to differences in magnitude and temperature dependence of effective thermal conductivity. We compared results with measured values from heritage materials and analyzed trends using a network model of effective thermal conductivity, incorporating the effects of porosity, grain size, Kapitza resistance, and individual constituent thermal conductivities.Y. Blum-contributing editor J. Marschall's contributions were

Lattice thermal conductivity of ultra high temperature ceramics ZrB2 and HfB2 from atomistic simulations

“…Thermal conductivity of polycrystalline ZrB 2 and Hf B 2 has been more thoroughly studied [8][9][10] . Room temperature measurements give 60W/(m · K) for ZrB 2 and 104W/(m · K) for Hf B 2 .…”

Material property requirements for analysis and design of UHTC components in hypersonic applications

“…3,52 Because the thermal conductivity of UHTC composites depends on many different factors, including microstructure, composition, defect and impurity levels, contact resistance between grains, and porosity, values cannot be estimated with any confidence from published data or measurements performed on individual constituents. Even nominally similar UHTC composites may not have the same heat transport characteristics, because the factors that affect thermal conductivity are largely determined by manufacturing details, for example, the raw ceramic powders sources, powder processing procedures, and hot-pressing schedules.…”

“…Specific heat is generally a strong function of temperature for UHTC materials, particularly from room temperature up to ∼1000 • C. For example, the specific heat of HfB 2 increases by about a factor of two over this temperature range. 52 While specific heat values for composite materials can be estimated from measurements performed on isolated constituents, values measured directly on the actual material are much preferred. Sample volumes used in calorimetry are often small.…”

“…Even nominally similar UHTC composites may not have the same heat transport characteristics, because the factors that affect thermal conductivity are largely determined by manufacturing details, for example, the raw ceramic powders sources, powder processing procedures, and hot-pressing schedules. 12,52 Thus thermal conductivities over the entire temperature range of interest must be measured for the exact UHTC material to be used in a particular component application.…”

Creep and Oxidation of Hafnium Diboride Based Ultra High Temperature Ceramics at 1500C

“…Surprisingly, HfB 2 's thermal conductivity decreases as temperature increases, leveling off around 70 W/(K m) by 800˚C [54]. However, Gasch shows that there are large differences in thermal conductivities depending on grain size and processing [57].…”