A. N. Suchkov

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.

Development of rapidly quenched nickel-based non-boron filler metals for brazing corrosion resistant steels

Corrosion-resistant steels are stably applied in modern rocket and nuclear technology. Creating of permanent joints of these steels is a difficult task that can be solved by means of welding or brazing. Recently, the use rapidly quenched boron-containing filler metals is perspective. However, the use of such alloys leads to the formation of brittle borides in brazing zone, which degrades the corrosion resistance and mechanical properties of the compounds. Therefore, the development of non-boron alloys for brazing stainless steels is important task. The study of binary systems Ni-Be and Ni-Si revealed the perspective of replacing boron in Ni-based filler metals by beryllium, so there was the objective of studying of phase equilibrium in the system Ni-Be-Si. The alloys of the Ni-Si-Be with different contents of Si and Be are considered in this paper. The presence of two low-melting components is revealed during of their studying by methods of metallography analysis and DTA. Microhardness is measured and X-ray diffraction analysis is conducted for a number of alloys of Ni-Si-Be. The compositions are developed on the basis of these data. Rapidly quenched brazing alloys can be prepared from these compositions, and they are suitable for high temperature brazing of steels.

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.

Brazing of zirconia-based ceramics to 29NK alloy using CTEMET 1202 amorphous tape brazing alloy

Abstract A method of brazing zirconia-based ceramics to 29NK alloy using CTEMET 1202 amorphous tape brazing alloy is developed. The efficiency of wetting the ceramics by the brazing alloy is evaluated. The structure and phase composition of the brazed joints were examined, shear strength determined and the microhardness of the brazed joints measured. The experimental results were used to select the optimum brazing temperature of ceramics to 29NK alloy.

Basic principles of creating a new generation of high- temperature brazing filler alloys

The development of new materials is based on the formation of a structural-phase state providing the desired properties by selecting the base and the complex of alloying elements. The development of amorphous filler alloys for a high-temperature brazing has its own features that are due to the limited life cycle and the production method of brazing filler alloys. The work presents a cycle of analytical and experimental materials science investigations including justification of the composition of a new amorphous filler alloy for brazing the products from zirconium alloys at the temperature of no more than 800 °C and at the unbrazing temperature of permanent joints of more than 1200 °C. The experimental alloys have been used for manufacture of amorphous ribbons by rapid quenching, of which the certification has been made by X-ray investigations and a differential-thermal analysis. These ribbons were used to obtain permanent joints from the spacer grid cells (made from the alloy Zr-1% Nb) of fuel assemblies of the thermal nuclear reactor VVER-440. The brazed samples in the form of a pair of cells have been exposed to corrosion tests in autoclaves in superheated water at a temperature of 350 °C, a pressure of 160 MPa and duration of up to 6,000 h. They have been also exposed to destructive tests using a tensile machine. The experimental results obtained have made it possible to propose and patent a brazing filler alloy of the following composition: Zr-5.5Fe-(2.5-3.5)Be-1Nb-(5-8)Cu-2Sn-0.4Cr-(0.5-1.0)Ge. Its melting point is 780 °C and the recommended brazing temperature is 800°C.

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.

Rapidly quenched strip brazing alloys for high-temperature brazing of niobium-based alloys

The composition of the brazing alloys for brazing niobium-based alloys is outlined. The method for producing brazing alloys based on Ti and Zr in the form of flexible strips is described. The relationships governing the formation of brazed joints are discussed.