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UHTC composites mechanical

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. [Pg.419]

Ceramic borides, carbides and nitrides are characterized by high melting points, chemical inertness and relatively good oxidation resistance in extreme environments, such as conditions experienced during reentry. This family of ceramic materials has come to be known as Ultra High Temperature Ceramics (UHTCs). Some of the earliest work on UHTCs was conducted by the Air Force in the 1960 s and 1970 s. Since then, work has continued sporadically and has primarily been funded by NASA, the Navy and the Air Force. This article summarizes some of the early works, with a focus on hafnium diboride and zirconium diboride-based compositions. These works focused on identifying additives, such as SiC, to improve mechanical or thermal properties, and/or to improve oxidation resistance in extreme environments at temperatures greater than 2000°C. [Pg.197]

Densities and open porosities of composites were measured by the Archimedes method. The mechanical properties of Cf/SiC-ZrC composites were tested through three-poinl-bending tests in an Instron-SS66 machine, operated at a crosshead speed of0.5mm/min and a span of 24mm, the dimensions of the testing bars were 4mmx2mmx40mm. The fracture surfaces and polished cross-sections of the composites as well as the surfaces and polished cross-sections of the UHTC coatings were observed by electron probe microanalyzer (EPMA, JXA-8100, Joel, Tokyo, Japan) to characterize the microstructures. [Pg.68]

In this section, the mechanical properties of carbides and borides of Zr-, Hf- and Ta-based composites are presented and correlated to the morphological features with particular attention to the effect of the secondary phases on the high temperature behaviour. The mechanical properties of the UHTCs presented in this chapter are summarized in Table 4. [Pg.164]


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See also in sourсe #XX -- [ Pg.210 ]




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UHTC composites

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