Joining technology—A challenge for the use of SiC components in HTRs

Abstract

The availability of suitable joining technologies is paramount to the further advancement of ceramic components and their use in HTRs. Among other joining technologies, a modified brazing technology using a laser beam for heating the components to be joined has been developed at TU Dresden.The laser-induced heating behavior of the ceramic material is determined by the interactions between the material and the laser beam. This was shown in two different silicon carbide materials (SSiC and SiCf-reinforced ceramic material) using a diode laser with wavelengths 808nm and 940nm.The laser-based technique was illustrated by three different examples: sealing of monolithic SiC with a pin configuration for fuel claddings, sealing of SiC heat pipes with a length of 1m, and demonstration of the transferability of the laser technique to fiber-reinforced components by means of a SiCf/SiCN material.Because the covalent bonding of SiC does not allow conventional welding, much research has been devoted to developing alternative filler systems. Glass or glass–ceramic fillers enable the tailoring of properties such as CTE and viscosity. Glasses are thermally stable up to their glass transition temperatures. It was shown that the crystallization of the yttrium aluminosilicate glass composition of the present work allows it to be used at 1050°C without any significant changes occurring in braze tightness. For the SiC heat pipes with sodium as the working fluid, a sodium-resistant metal braze consisting of Ni–Ti–Si was formed. The long-term resistance of this filler to sodium at 800°C was proven. The results demonstrate the possibility of using the laser-based joining technique for the joining of different SiC materials as well as for different brazing materials.