Oxidation mechanisms of ZRB2-based ultra high temperature ceramic matrix composites

Conference Dates

November 5-9, 2017


Ultra-high temperature ceramics (UHTCs) are expected as the materials for the nose cones and leading edges for hypersonic and re-entry vehicles. Zirconium diboride (ZrB2) and its composites are a widely studied class of UHTCs. The oxidation of monolithic ZrB2 forms ZrO2 and B2O3. B2O3 acts as a surface protective layer; however, it evaporates above 1200℃. SiC particles are considered effective additives because the SiO2 formed by the oxidation of SiC protects the unreacted region. Simultaneously, excessive pores are formed under the surface in the SiC particle-dispersed ZrB2 matrix (hereafter denoted ZS) composites in a wide temperature range by the preferential oxidation of SiC (active oxidation of SiC) because solid SiO2 is not formed; instead, gaseous SiO forms by active oxidation because of the low oxygen partial pressure relative to that of the surface. The pore-rich porous layer is denoted the “SiC-depleted layer”. The SiC-depleted layer leads to spallation and delamination of the oxidized regions on the surface because strength and stiffness of this layer are quite low. Thus, excessive pore formation in ZS composites should be prevented to improve the oxidation resistance.

The objective of this study is to understand oxidation mechanisms of ZrB2-based composites and to propose the way to prevent the formation of SiC-depleted layer in ZS composites. In the present study, we fabricated monolithic ZrB2, ZS, and ZrB2-SiC-ZrC (ZSZ) ternary composites by spark plasma sintering (SPS) technique. In addition, carbon fiber-reinforced ZSZ matrix (C/ZSZ) composites was also fabricated by Si melt infiltration (MI) process. Oxidation resistance of monolithic ZrB2, ZS, ZSZ, and C/ZSZ have specially designed fast heating system in order to characterize oxidation resistance above 2000℃.

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