Journal of the American Ceramic Society, Vol.102, No.9, 5645-5655, 2019
Evaluation of rare-earth element dopants (Sm and Er) on ablation resistance of ZrB2/SiC-sintered billets
In this paper, how rare-earth element dopants (samarium and erbium) affect the scale development of sintered ZrB2/SiC (ZBS) samples during ablation testing was investigated. ZBS billets with five different Sm to Er ratios, with a nominal total amount of 3mol% dopant incorporated, were prepared by sintering in vacuum to 2000 degrees C and subjected to 60 and 300seconds ablation cycles. Differences in surface temperatures between ZBS samples with different dopant ratios suggests differences in spectral absorptance/emittance between each of the five compositions investigated. ZBS billets co-doped with Sm and Er form a beneficial c(1)-(Sm/Er)(0.2)Zr0.8O1.9 oxide scale as the majority phase, with some glassy phase observed. The crystalline c(1)-(Sm/Er)(0.2)Zr0.8O1.9 oxide scale is more thermally stable than the m-ZrO2 oxide scale typically formed in oxidized ZBS systems, resulting in a more adherent oxide scale to the unreacted material. The crystalline oxide scale and the amorphous phase are formed by a convection cell mechanism where the c(1)-(Sm/Er)(0.2)Zr0.8O1.9 crystalline islands precipitate, grow, and coalesce.