Preparation and rheological behaviors of a nano-yttria anti-bonding paste

Anti-bonding pastes are used on areas that should not be welded during superplastic forming/diffusion bonding processes in multi-layer, complex metal structures. We prepared a nano-Y2O3 anti-bonding paste to prevent the coated anti-bonding paste from flowing to unwanted areas and to improve the thickness uniformity of the coated paste. Nano-spherical Y2O3 powders with a purity of more than 99.99 wt% and a narrow size distribution of 50 to 100nm were prepared by liquid precipitation followed by sintering. The relationship between the rheological behaviors and dispersion structure of both pastes with and without 1.5 wt% rheology control additive was analyzed in detail. The results indicated that a strong three-dimensional network flocculation structure had formed in the pastes, especially in those with a rheology control additive. The resulting large yield stress, high thixotropy, and solid-like elastic behavior of the paste are favorable for maintaining the original coated shape and offer long-term stability, but are unfavorable for the screen printing (coating) process and thickness uniformity. To solve these problems, a high printing pressure and the use of a screen with high tension and large mesh count (325 mesh) could be adopted. The thermal analysis results show that the paste after SPF/DB processing was easy to clear with no negative influence on the process.