O. N. Sevryukov

BE-CU JOINTS BASED ON AMORPHOUS ALLOY BRAZING FOR DIVERTOR AND FIRST WALL APPLICATION

Abstract The limitation on using silver-based alloys for brazing ITER in-vessel components created a development problem for new brazing materials. An application of Be tiles joined to a Cu-based heat sink will be discussed in this paper. For this purpose, rapidly solidified ribbon-type filler metal STEMET 1108 1 (Cu–Sn–In–Ni system) with a melting temperature of 750°C and a thickness up to 50 μm was developed. A new temperature regime and heating method were applied during this brazing procedure. This improves the properties of joints significantly, in comparison with conventional brazing in a resistance furnace. These treatments can increase the operational threshold for Be/Cu joints under cyclic surface heat loading up to 12 MW/m2. Metallographic examinations demonstrated the high quality of brazed joints. The brazed seam has a uniform structure along its entire length. Defects of seam filling, pores, intermetallic compounds and other inclusions are not seen. The prospects of these joints for fusion reactor applications are discussed.

Application of amorphous and microcrystalline filler metals for brazing of beryllium with metals

Abstract Rapidly solidified (RS) amorphous and microcrystalline ribbon-type brazing filler metals (FMs) represent a promising facility for joining heterogeneous materials together. The advantage results are followed from the homogeneity of element and phase compositions and the strictly specified geometrical dimensions of such FMs. Produced by rapid solidification technology amorphous FM: Zr Ti Fe Be (STEMET 1

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

Abstract 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 μm in comparison with that of 8 to 10 μm 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.

Brazing of the ITER First Wall by a Copper-Based Rapidly Quenched Ribbon-Type Filler Metal

Abstract As applied to the manufacture of the ITER first wall, a rapidly quenched copper-based filler metal for brazing chromium-zirconium copper alloy (CuCrZr) with beryllium (Be) at temperatures below 720°C has been selected. The composition of the given filler metal has been optimized by varying the concentration of alloying elements, such as Sn, Ni, and P, improving the filler functional properties and quality. Rapidly quenched ribbon-type filler metals with various contents of alloying elements were investigated by differential thermal and X-ray phase analysis, atomic force microscopy, and scanning electron microscopy. To improve the casting performance of the filler metal and obtain high-quality ribbons, the kinematic viscosity of brazing alloys with various contents of Ni, Sn, and P has been investigated. The chromium-zirconium copper alloy has been brazed with Be using the filler metals obtained (by furnace brazing and fast brazing by passing an electric current). Based on the results of complex research, an ultrafast (quenching rate of ∼105°C/s) quenched brazing alloy STEMET 1101M (Cu-9.1Ni-3.6Sn-8.0P, in weight percent) has been selected and manufactured in the form of a ribbon that is 50 mm in width and 50 μm in thickness. An experimental mock-up of the ITER first wall has been made in D.V. Efremov SRIEA by rapid brazing (by passing a current) using the filler metal STEMET 1101M. The brazed joint has withstood 15 000 cycles of thermocycling under a thermal load of 0.5 to 5.9 MW/m2 without breaking.

Study of the Ni–Si–Be system as a base to create boron-free brazing filler metals

ABSTRACT The investigation results of alloys of the Ni–Si–Be system with a various content of Si and Be are presented. Two low-melting eutectics with melting temperatures of the order of 1100 and 915°C have been found out by the methods of differential thermal and X-ray phase analysis and metallography. Two alloys have been selected for the development of brazing filler metals: Ni–5Si–3Be and Ni–6Si–5Be alloys. Three phases have been shown to be components of the binary and ternary eutectics in the Ni–Si–Be system from the side of the nickel angle of the phase diagram. A Ni–5Si–3Be ribbon and fragments of the Ni–6Si–5Be ribbon have been obtained from the selected alloys by rapid quenching. Filler metal of the Ni–5Si–3Be system has been used for brazing samples of the 12Cr21Ni5Ti austenitic–ferritic corrosion-resistant steel at 1150°C for 30 min.

Selection of materials for tokamak plasma facing elements based on a liquid tin capillary pore system

Capillary-Pore Systems (CPS) filled by liquid metals are considered as an alternative solution of materials choice for plasma facing component of tokamak reactor. Tin is viewed as one of the candidates for CPS because it has lower corrosiveness than gallium and lower saturated vapour pressure compared to lithium. The corrosion resistance of Mo, Nb and W in pure liquid tin was investigated. The corrosion tests were carried out in the static isothermal conditions at a temperature up to 1050°C. As a result of the corrosion study, it was found that Mo does not corrode in liquid Sn, as opposed to Nb and is compatible with liquid tin in temperatures of up to approx. 1000°C. This allows considering Mo as an alloy base material of the in-vessel tokamak elements based on liquid tin capillary pore systems.

Brazing of hexagonal boron-nitride ceramics with VT1-0 titanium alloy using a rapidly quenched titanium-based brazing alloy

A brazing alloy was developed for the brazing of boron-nitride ceramics with VT1-0 alloy in the form of nanostructured rapidly quenched tapes. The wetting capacity of the boron-nitride ceramics by the brazing alloys of the Ti–Zr system is evaluated. The surface of the brazing alloy tape was investigated by X-ray diffraction and topographic methods and the brazed joints between theVT1-0 titanium alloy and boron-nitride ceramics were studied by examination of microstructure and mechanical properties.

The brazing of nickel alloys for nuclear reactor with the using of the rapidly-quenched filler metals

The possibility to apply amorphous nickel-based braze alloys for junction of nickel-alloy products used in the control and protection devices of nuclear power plants is demonstrated. Mechanical tests and investigations of the structural phase state of brazed junctions are carried out.

Structural phase transformations and changes in the surface topology upon crystallization of amorphous alloys based on nickel

The changes in the structure, phase composition, and topology of the surface of rapidly solidified metallic glasses Ni71.5Cr6.8Fe2.7B11.9Si7.1 and Ni63.4Cr7.4Fe4.3Mn0.8B15.6Si8.5 are investigated after three stages of crystallization. The surface topology changes are found to be correlated with the processes occurring at different stages of crystallization. The character of the redistribution of chemical elements in the crystallized alloys is ascertained.

Brazing ferritic-martensitic reactor steels with an amorphous rapidly quenched nickel-based strip brazing alloy

A brazing alloy has been developed for brazing ferritic-martensitic steels. The technology for producing the brazing alloy based on nickel in the form of amorphous ribbons is described. Steels EP-450 DUO and EP-823 were brazed using the new brazing alloy. The relationships of the formation of brazed joints were determined. The results of brazing trials on models of fuel elements made of steels ChS-139 and EP-823 (EP-450 DUO) and the mechanical tests of the brazed joints (shear test) are presented.