Preparation and Thermal Ablation Behavior of HfB₂–SiC‐Based Ultra‐High‐Temperature Ceramics Under Severe Heat Conditions

Abstract

HfB 2 -SiC-based ultra-high-temperature ceramics with aluminum nitride (AlN) as a sintering aid were hot pressed at 18501C. The sinterability and mechanical properties were investigated and compared with the composite without a sintering aid. It was shown that the addition of AlN greatly improved the powder sinterability and enabled the production of a nearly full-dense composite. The mechanical properties, especially the flexural strength, were enhanced remarkably through the improvement in the sinterability and microstructure. The oxidation resistance of a composite doped with 10 vol% AlN was evaluated by a plasma arc heater and the ablation mechanism was discussed.

Plasma wind tunnel testing of ultra-high temperature ZrB2–SiC composites under hypersonic re-entry conditions

“…SiC + 3/2O 2 = SiO 2 + CO(g) (2) that yield oxide by-products like zirconia (ZrO 2 ), boron oxide (B 2 O 3 ) and silica (SiO 2 ). Boron oxide, which melts at 450 • C, promptly mixes with SiO 2 for temperatures above 1200 • C to form a borosilicate glass that spreads over and seals the external surfaces.…”

“…Ultra-high temperature ceramics (UHTCs) containing transition metal borides are under intensive analysis for applications in extreme environments, [1][2][3] where high-temperature aerospace applications on hypersonic vehicles have been the most investigated.…”

“…Cross-sectioned and polished blunt hemisphere (tip area, back-scattered electron SEM micrograph): outermost glassy layer decorated with tiny zirconia particles (1), oxide sub-layer(2). Large zirconia crystals are indicated.…”

Effect of AlN Substitutions on the Oxidation Behavior of ZrB2–SiC Composites at 1600°C

“…Al 2 O 3 , on the other hand, will persist at elevated temperatures, and is known to reduce the viscosity of silicates and will, therefore, possibly enhance the oxidation resistance . Furthermore, Li et al and Zhang et al reported improved ablation resistance with AlN addition. Therefore, it is important to ascertain the oxidation resistance of ZrB 2 –SiC modified by an alumina former such as AlN.…”

Synthesis of Ultrafine Hafnium Diboride Powders Using Solution‐Based Processing and Spark Plasma Sintering

“…Due to its remarkable properties of high melting point, Young's modulus, hardness, thermal conductivity, and excellent corrosion resistance, HfB 2 has been considered as a good potential material for ultrahigh temperature applications in the aerospace industry. [1][2][3] However, densification of monolithic HfB 2 is very difficult due to its high melting point, strong covalent bonding, and low self-diffusion rate. The densification of HfB 2 has been influenced by the properties of the HfB 2 powder, such as purity, morphology, surface area, and defects concentration.…”