UHTC composites

Basic property evaluation of UHTCs and UHTC composites has resumed at a number of government facilities within NASA and the military, as well as at some universities. " With this resurgence in basic research, investigations into UHTC carbides and nitrides are seeing added attention as new processing techniques make the fabrication of these materials easier. 

R. Licheri, R. Orru, C. Musa and G. Cao, "Combination of SHS and SPS Techniques for the Fabrication of Fully Dense ZrB2-ZrC-SiC UHTC Composites", Materials Letters, 62, 432-435 (2008). 

Marschall D. John. Oxidation and Catalytic Efficiency of ZrB2 and HfB2 based Ultra-High Temperature Ceramic (UHTC) Composites Exposed to Supersonic Air Plasma. 2004 1. 

The characteristics and sources of reactants used for the synthesis by SHS of the binary and ternary UHTC composites are reported in Table 2. Mixing of reactants was performed in agreement with the following reactions stoichiometry ... 

Table 3. Enthalpies of formation of UHTC composites according to reactions (1)-(6) (Barin, 1989), related combustion temperatures (TJ and average reaction front velocities (v) measured during SHS...

Figure 7. SEM back-scattered micrographs of spark plasma sintered UHTC composite materials (a) ZS, (b) HS, (c) TS, (d) ZZS, (e) HHS, and (f) TTS (adapted from Licheri et al., 2007 Licheri etai, 2008 Licheri et al., 2009 Licheri etal., 2010b)...

Table 5. Properties of bulk UHTC composites obtained by SPS...

RMI is applicable for preparing C/UHTC composite. In RMI, liquid metal melt penetrates into a porous C/C preform under an inert atmosphere or a vacuum condition. The metal melt expands to fill the pores, ultimately resulting in a dense... 

REACTIVE MELT INFILTRATION OF C/UHTC COMPOSITES 3.1 C/SIC COMPOSITES DOPED WITH UHTC... 

On account of very low ceramic yields from these chlorides and low molecular compounds, it is difficult to obtain a matrix with high ZrC/ZrB volume fraction. A binary matrix of ZrC(or ZrB ) with SiC can only be proceeded separately leading to alternating formation of ZrC(or ZrB ) and SiC, therefore these two phases exhibit a sandwiched microstructure, which differs from the homogeneous dispersed UHTCs composite prepared by hot-pressing. 

In this chapter, the pyrolysis of synthesized polymers, microstructure of their derived UHTC composite matrices, as well the preparation and properties of C/C-ZrB2-ZrC-SiC composites are investigated. Preparation and microstructures of the composites were studied in part I of the paper. The ablation behaviors and mechanical properties of the composites in a ground arc-jet wind tunnel and plasma torch with temperatures above 2000 °C and heating rate around 30K/s were studied in Part II. The major aims of these studies were to evaluate the possibility of producing a nano-size dispersed ZrB -ZrC-SiC matrix using these complex polymeric precursors, which are expected to exhibit improved oxidation and ablation resistance, compared to those composites with layered or large particle incorporated UHTC matrices. 

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