HfC-Based Composites

Sciti, D., Silvestroni, L., Bellosi, A. (2006). High-density pressureless-sintered HfC-based composites. Journal of the American Ceramic Society, 89,2668-2670. doi 10.1111/j.l551-2916.2006.01109.x. 

The XRD pattern acquired from the HfC-based composite revealed the presence of cubic HfC and tetragonal MoSi. ... 

The first carbonitride alloys based on Ti(C,N)—Ni—Mo were iatroduced ia 1970 foUowed by (Ti, Mo)(C,N)-based compositions having fine microstmctures that provided a balance of wear resistance and toughness (4). Continued research on the titanium carbonitride alloys, often called TiC—TiN cermets, ia the 1980s led to the developmeat of complex cermets having a variety of additives such as molybdeaum carbide(2 l) [12069-89-5] M02C, TaC, NbC, zirconium carbide [12020-14-3], ZrC, hafnium carbide [12069-85-1], HfC, WC, vanadium carbide [12070-10-9], VC, chromium carbide (3 2)... 

Identification of unknown crystal structures and determination of phase fields by X-rays can be problematical if the characteristic patterns of the various phases are quite similar, for example in some b.c.c. A2-based ordered phases in noble-metal-based alloys. However, in many cases the characteristic patterns of the phases can be quite different and, even if the exact structure is not known, phase fields can still be well established. Exact determination of phase boundaries is possible using lattice-parameter determination and this is a well-established method for identifying solvus lines for terminal solid solutions. The technique simply requires that the lattice parameter of the phase is measured as a function of composition across the phase boimdary. The lattice parameter varies across the single-phase field but in the two-phase field becomes constant. Figure 4.12 shows such a phase-boundary determination for the HfC(i i) phase where results at various temperatures were used to define the phase boundary as a fimction of temperature (Rudy 1969). As can be seen, the position of is defined exactly and the method can be used to identify phase fields across the whole composition range. 

A third class of hydrides, the AB5 type (Latki Hfc), also function at ordinary temperatures and are easily activated, but are costly due to the presence of lanthanum. Investigations seeking lower cost substitutes for lanthanum have resulted in the development of two useful alloys. One is based on the substitution of cerium-free Mischmetal (M), an unrefined rare-earth alloy the second is based on the substitution of calcium (Ca) and Mischmetal. These compositional changes have reduced the raw materials costs to about 30% of that for LaNi5 alloy, but further cost reductions are required. 

Composition and structure of the individual polycyclic compounds, synthesized by fractionation in high vacuum, were determined on the basis of the ultimate analysis by determination of the molecular mass, IR and H NMR spectral data. Based on this reaction, the authors have concluded that 1,5-dichlorohexaphenylcyclotetrasiloxane used in HFC reactions represents a mixture of cis- and traws-isomers. The c/.v-form promotes for structures... 

Entrants were provided with the experimental bubble points for 15 mixture compositions of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) and ethanol at 283.17 K, and properties of the pure materials at 343.13 K. The challenge was to compute bubble points for seven mixture compositions at 343.13 K, using any experimental data for the pure components but the only mixture points at 283.17 K. Entries using any theory/modeling/simulation method were accepted. Entries were judged based on the criterion. 

Based on the successful experiences in producing C/ZrC composite by RMI, Ultramet developed a carbon fiber reinforced HfC composite (C/HfC) with 2 inches thick by a rapid RMI process. The processing is virtually independent of part size and shape, making it applicable for net-shape fabrication of pintles and throat for a broad variety of solid rocket motors. 

Ye, Y. C., Zhang, H., Zhu, L. A., Tong, Y. G., Chen, K., Bai, S. X. (2012). Preparation of C/HfC composites by instantaneons liqnid in-filtration at low temperature based on alloy design and its ablation property. 2nd International Conference on Advanced Composite Materials and Technologies for Aerospace Applications. Wrexham, UK. 

---