B. A. Kalin

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

Microstructure development and helium behavior in nickel and vanadium base alloys

Abstract Transmission electron microscopy and thermal helium desorption spectrometry (TDS) have been used to investigate the influence of alloying elements on helium behavior and bubble microstructure evolution in FCC (Ni+1…7.5 wt%Al) and BCC (V+10…40 wt%Ti) metals. The samples were irradiated by 40-keV He+ ions at room temperature up to a fluence of 5×1020 m−2. Post-irradiation annealings were performed at 1023 K (Ni–Al) and 1075 K (V–Ti) for 1 h. It was shown that alloying elements reduced the bubble size ( d b ) and increased their density (ρb) in both types of alloys. In the Ni–Al alloys the TDS peaks are displaced to higher temperatures with increasing Al concentration in contrast to V–Ti alloys where the TDS peaks are displaced to lower temperatures with increasing Ti content. However in both systems of alloys the effective activation energy for helium desorption grows with alloying element concentration. The results are discussed in terms of alloying element influence on the mechanisms of bubble growth and migration.

Influence of alloying elements in Ni and Fe on ion-implanted helium behavior

Abstract Behavior of ion-implanted helium and bubble microstructure evolution in Ni-base (Ni C, Ni Al) and Fe-base (Fe C) model alloys, as well as in homogeneous austenitic 16–15 type steel with various carbon contents and in age hardening 15–35 type steel as a function of alloying element concentration, have been investigated by means of thermal desorption spectrometry (TDS) and transmission electron microscopy (TEM). The results show the different nature of influence of carbon and aluminium on bubble parameters formed during postirradiation annealings. Calculated by means of the ‘tempering’ method, helium release effective activation energy proved to be higher for alloys than for pure metals. The effect of these observations is discussed from the standpoint of diffusion parameter change in metals by alloying.

Influence of external action and structural factors on radiation blistering

Abstract A survey of experimental results is presented, pertaining to radiation blistering of a considerable number of materials (stainless steels, alloys with high nickel content, alloys of refractory metals) under helium ion irradiation with energies of 20–100 keV under conditions corresponding to the plasma-wall interaction: bombardment at various angles of incidence and cyclic irradiation in a wide spectrum of ion incidence angles; influence of external action, including thermocycling; influence of preceding neutron and proton irradiation. It has been shown that external factors have a complex influence on blister parameters and erosion coefficients of materials. A study has been carried out on the influence of aluminium coatings, alloying additions, phase state of material and microstructure on the nature and degree of surface erosion. Complex influence of element and phase composition, as well as microstructural changes during heat treatment and welding on radiation erosion have been established.

Investigation of oxygen-titanium interaction in vanadium by internal friction method

The temperature dependences of the internal friction, Q−1, of vanadium and of V-(0.3–10%) Ti alloys are measured in the range from room temperature to 900°C. Three peaks at 227, 295, and 375°C attributed to the O-V, O-Ti, and Ti-V complexes are detected for the alloys with a low content (<5%) of titanium. In the alloys containing 5–10% titanium, these peaks disappear, but a new peak attributed to the V-O-Ti complex arises at 475°C. The binary complexes are found to make the main contribution to retardation of dislocations in the V-Ti alloys with a low content of titanium and, consequently, to strengthening and embrittlement of these alloys.

Formation of Gas Pores in Nickel Alloys and Structural Steel under Irradiation by Helium Ions

Transmission electron microscopy is used to study the development of helium porosity in binary alloys of nickel with elements possessing a different dimensional atomic mismatch with nickel – from negative (beryllium and silicon) to positive (molybdenum, tungsten, aluminum, titanium, tantalum, tin, and zirconium), in structural steels ChS-68, ÉP-150, and the nickel alloy KhNM. The gas pores were produced by irradiation with 40 keV He+ up to fluence 5·1020 m–2 at 650 and 20°C followed by annealing at 650°C for 1 h. It is shown that under high-temperature annealing beryllium and silicon, relative to nickel, give rise to the formation of larger bubbles, while elements with a larger positive size mismatch with nickel atoms substantially decrease the size and increase the density of the bubbles. On the whole, as atomic radius and the concentration of the alloying element increases in alloys, the gas swelling of the irradiated layer decreases. Under post-irradiation annealing, bubbles with the largest diameter and the lowest density develop in nickel. Any alloying used decreases the size and increases the density of bubbles. The data obtained are discussed from the standpoint of the formation of various vacancy complexes of helium and their thermal stability.

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 a method for producing metal materials with a nanostructured surface layer by treatment with high-energy pulsed plasma

The formation of nanocrystal layers on the surface of various steels is experimentally studied; this procedure is performed by cladding of the surfaces with rapidly quenched metal filler alloys followed by treatment with a high-energy pulsed plasma. It is shown that the plasma treatment of the clad samples leads to the formation of a homogeneous cellular nanostructure with cells 50–150 nm in size.

Radiation damage of material surfaces under prolonged irradiation with He + and Ar + ions with broad energy spectra

The results of studying the redistribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms incorporated in polycrystalline metal samples under irradiation with He+, (He+ + Ar+), and Ar+ ion beams with a broad energy spectrum and an average energy of 10 keV at irradiation doses of 1 × 1021 ion/cm2 are studied. It is discovered that irradiation at doses exceeding 1 × 1019 ion/cm2 results in local small-crystal formations being produced in a near-surface substrate layer. Their typical dimensions are less than 1–5 μm, and their the density is up to 1–100. They contain incorporated atoms and impurity atoms with a concentration of 0.1–10 at %. Subsequent irradiation at a dose of 1 × 1020 ions/cm2 or more leads to disappearance of these formations, mainly because of sputtering processes.