Application of Rapidly Quenched Ribbon-Type Filler Metals for Brazing of the High-Heat-Flux Elements of ITER

Rapidly quenched ribbon-type filler metals of the systems of Cu-Sn-In-Ni-Mn-P (STEMET® 1108) and Cu-Ti-Be (STEMET 1204M) for brazing of high-heat-flux elements of ITER were developed at National Research Nuclear University (NRNU) Moscow Engineering Physics Institute (MEPhI) together with D.V. Efremov Scientific Research Institute of Electrophysical Apparatus (SRIEA).

The technological brazing parameters of the joints of beryllium with bronze (CuCrZr)-Be-CuCrZr ("rapid brazing" by an electron beam) and tungsten with bronze (CuCrZr)-W-CuCrZr (vacuum brazing in a furnace) were improved by the filler metals obtained. It is shown that under rapid brazing it is possible to minimize the Be₂Cu intermetallic layer thickness between the filler metal and beryllium up to 1 to 1.5 m in comparison with that of 8 to 10 m obtained in brazing in a furnace with resistive heating and to avoid weakening of bronze (CuCrZr). Brazing of W-CuCrZr was successful in completely dissolving the alloying components of the filler metal in the bronze base and obtaining a joint without a transition layer.

A complex of metallographic, mechanical, and thermocycling tests of the brazed joints obtained was carried out. It is shown that the brazed seam width (for rapid brazing of Be-CuCrZr) and the brazing zone morphology do not change during the annealing (at 300°C for 100 h) and thermocycling tests (1000 cycles at 5 and 8 MW/m²). The brazed joints of Be-CuCrZr obtained by rapid brazing withstood 4500 cycles at the thermal load of 12 MW/m² and 1000 cycles at 13.5 MW/m². The maximum thermal load achieved at screening was 16 MW/m². It is established that under irradiation by pulsed deuterium plasma flows from the end surface of brazed joints of tungsten with copper-base heat-removing alloys using a hard irradiation parameter (W = 5 MW/cm²), the joint of monocrystal tungsten with bronze CuCrZr brazed by the STEMET 1204M filler metal has the highest thermal stability.

It is shown that neutron irradiation (at a fluence of 1.8 × 10²⁰ n/cm² with a neutron energy >0.1 MeV, at 200°C) does not result in weakening of the W-CuCrZr brazed joint.