Microstructure evolution and ablation mechanisms of Csf/ZrB2-SiC composites at different heat fluxes under air plasma flame.

In this study, short carbon fibre (C sf) reinforced ZrB 2 -SiC composites were fabricated via direct ink writing followed by precursor infiltration and pyrolysis. The ablation behaviour of the composites was investigated at heat fluxes of 4–6 MW/m2 under an air plasma flame, which revealed excellent ablation resistance with negative linear ablation rates of − 0.1 to − 0.5 µm/s. The results showed that ZrO 2 -SiO 2 oxide layer was formed on the ablation surface after ablation, which provided effective protection to the internal materials. With an increase in heat flux, ZrO 2 precipitated from the SiO 2 melt first in the form of nano-tetragonal ZrO 2 (t -ZrO 2), owing to the vaporisation of SiO 2. During cooling, the nano t -ZrO 2 particles were retained, and some of them reacted with SiO 2 to form ZrSiO 4 , thus improving the thermal stability of the SiO 2 -ZrO 2 oxide layer. In contrast, t -ZrO 2 agglomerated and grew owing to capillary force and finally transformed into monoclinic ZrO 2 (m -ZrO 2). Moreover, a higher heat flux led to the size of precipitation ZrO 2 increases, meanwhile increasing the content of t -ZrO 2 and ZrSiO 4 in the oxide layer. • Short carbon fibers reinforced C sf /ZrB 2 -SiC composites were fabricated by direct ink writing, followed by precursor impregnation and pyrolysis. • During cooling, the nano t -ZrO 2 particles were retained, and some of them reacted with SiO 2 to form ZrSiO 4 , thus improving the thermal stability of the SiO 2 -ZrO 2 oxide layer. • The capillary force leads to the nano crystals gradually agglomerate and form dendritic structure. • From 4 to 6 MW/m2, the size of the dendritic structure ZrO 2 increased. [ABSTRACT FROM AUTHOR]