Preparation and hydrogen diffusion evaluation of the yttrium oxide dispersed tungsten matrix for use in nuclear thermal propulsion

The fissile fuel loss in tungsten (W) based ceramic-metal (Cermet) element used in nuclear thermal propulsion is of great importance. In this study, the W-Y 2 O 3 composite matrix was manufactured tentatively by Spark Plasma Sintering (SPS) to relieve the fuel loss. Performance evaluation of hydrogen (H 2 ) permeation and diffusion behaviors in the matrix was carried out by a gas permeation device. The results indicate that the diffusion coefficient of H 2 in the pure W matrix is nearly 10 times larger than that in the W-Y 2 O 3 matrix at a test temperature of 823 K. Based on the results, a careful investigation of the fuel loss mechanism of the Y 2 O 3 dispersed W matrix was performed. SEM and TEM showed that the fine Y 2 O 3 particles are distributed along grain boundaries of the W ternary-phase and present a distinct transition region of about 10 nm between the Y 2 O 3 and W phases. In particular, the crystallographic orientation relationship suggests that a semi-coherent structure is formed at the W/Y 2 O 3 phase interface : (0 1 −1) W || (1 0 −1) Y 2 O 3 and [0 1 1] W || [1 1 1] Y 2 O 3 . This semi-coherent structure is favorable for binding the two phases together tightly, thus hindering the inward diffusion of H 2 greatly. Moreover, the improved density and refined size of the W grains are achieved. Therefore, there is no doubt that the dispersion of Y 2 O 3 is beneficial for lowering the H 2 diffusion rate in the W matrix and thus reducing the fuel loss effectively. This work furthers our understanding of the key role of Y 2 O 3 in the W matrix used in nuclear thermal propulsion.