| Abstract: |
Plasma spraying ZrB2 ceramic coating is considered as potential candidate method of Thermal Protective System. While the application of plasma sprayed ZrB2 coating is restricted due to its oxidation. Therefore, it is important to study the oxidation behavior of the ZrB2 material, as it can contribute to improving oxidation resistance of plasma sprayed ZrB2 coating. The pores in ZrB2 ceramics can influence the oxidation behavior, but ZrB2 ceramic can not achieve very high density using plasma sprayed. So oxidation mechanism of ZrB2 ceramic with few pores is less clear. In this research, oxidation behavior of the ZrB2 ceramic, which achieve very high density by using spark plasma sintering (SPS), is studied.
The oxidation behavior of ZrB2 ceramics is investigated using SEM, XRD and STA. The density of SPS ZrB2 ceramics significantly increase when adding SiC and WC. The relative density of pure SPS ZrB2 ceramics is 72%. The addition of SiC or WC increases the relative density of ZrB2 ceramics to 90%~95%. Further, the addition of both SiC and WC increases the relative density to 99%, which reveal a synergy between SiC and WC. Based on the date from TG experiment, the high density has some beneficial effect to improve the oxidation resistance of ZrB2 ceramic, especially under low oxidation temperature (below 1000), for there are few open pores channel in high density ceramics. The oxygen can not diffuse to the inner through pores, as a result, the high density ceramics can only be oxidized from outside to inside progressively, unlike low density ceramics, whose surface and inner is oxidized simultaneously until the surface is covered by glass phase. In addition, the ZrO2 layer of oxidized high density ZrB2 ceramics is scattered grainy structure, which is supposed to be oriented growth in oxidized low density ZrB2.
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