Research on Joining of Dissimilar Materials in Massive Scientific Facility

Author: CHEN Jichun , LI Zhenglin , HAO Chuanyong

In magnetic confinement nuclear fusion, a strong magnetic field is used as "magnetic container" to confine high-temperature plasma which is then heated to hundreds of millions of degrees to maintain continuous thermonuclear reactions. Because the fusion reactors are made of a wide variety of materials, the need to join dissimilar materials is apparently prevalent. Furthermore, all the joints are always subject to higher heat loads and serious plasma sputtering erosion. Accordingly, the joint reliability is of intense importance. However, joining of dissimilar materials with huge differences in composition, physical and chemical properties has always been the biggest bottleneck restricting their engineering applications.

For the first time, we completed the preparation of the negative ion source plasma grids and became a bulk supplier for EAST and HL-2M, resolving the joining technologies for some critical material combinations such as Mo/Mo, Mo/stainless steel and Mo/OFC. We successfully manufactured the negative ion source Faraday shield, breaking through the key technologies for large-area diffusion bonding of OFC and precision brazing of OFC/stainless steel assemblies. We developed a precision brazing technology for diamond-shaped cross section molybdenum rails. Ultra-high precision procedure (post-braze dimensional tolerance: ±0.02 mm) were accomplished with 14 diamond-shaped cross section molybdenum tubes, 28 miniature metal bellows and stainless steel holders. No leak was identified in post-braze helium leak testing of the 86 brazing seams (the leakage rate was less than 1×10-10Pa?m3/s).

The proposed technologies for joining of dissimilar materials provide strong support for the construction and maintenance of the magnetic confinement nuclear fusion devices in China. Furthermore, in the next 10 years, China will gradually build nuclear fusion power station to generate electricity, and the application prospects of our researches will be broad and the economic value will be huge too.

Fig. 1. Key parts of magnetic confinement nuclear fusion. (A) Faraday shield; (B) diamond-shaped cross section molybdenum rails; (C) plasma grid.