A.S. Pokrovsky

Low-temperature radiation embrittlement of copper alloys

The effect of low-temperature (T{sub irr} less than 0.3. T{sub melt}) irradiation on the tensile properties of copper and precipitation-hardened (PH) and dispersion-strengthened (DS) copper alloys was investigated. Samples were irradiated with fission neutrons at temperatures of 80 to 200{degrees}C to doses of 0.6 to 5 dpa. Irradiation at temperatures <150{degrees}C resulted in significant hardening and accompanying embrittlement in all of the materials. By comparing the present results with literature data, it is concluded that severe radiation embrittlement occurs in copper alloys irradiated at temperatures {le}I00{degrees}C for doses above {approximately} 0.01 to 0.1 dpa. On the other hand, irradiation at temperatures above 150{degrees}C causes only moderate embrittlement for doses up to {approximately}5 dpa. It is recommended that the minimum operating temperature for copper alloys intended for structural applications in fusion energy systems should be 150{degrees}C, unless uniform elongations

The effect of neutron spectrum on the mechanical and physical properties of pure copper and copper alloys

The electrical resistivity and tensile properties of copper and oxide dispersion strengthened (DS) copper alloys have been measured before and after fission neutron irradiation to damage levels of 0.5 to 5 displacements per atom (dps) at {approximately}100 to 400{degrees}C. Some of the specimens were irradiated inside a 1.5 mm Cd shroud in order to reduce the thermal neutron flux. The electrical resistivity data could be separated into two components, a solid transmutation component {Delta}{rho}{sub tr} which was proportional to thermal neutron fluence and a radiation defect component {Delta}{rho}{sub rd} which was independent of the displacement dose. The saturation value for {Delta}{rho}{sub rd} was {approximately}1.2 nanohm-meters for pure copper and {approximately}1.6 nanohm-meters for the DS copper alloys irradiated at 100{degrees}C in positions with a fast-to-thermal neutron flux ratio of 5. Considerable radiation hardening was observed in all specimens at irradiation temperatures below 200{degrees}C. The yield strength was relatively insensitive to neutron spectrum in specimens strengthened by dispersoids or cold- working. 17 refs., 7 figs., 1 tab.

The effect of neutron irradiation on the electrical resistivity of high-strength copper alloys

The effects of neutron irradiation on the electrical resistivity of precipitation hardened (PH) and dispersion strengthened (DS) copper alloys are discussed. The analysis is based on the experimental study of radiation damage of PH and DS copper alloys, irradiated in the fast neutron reactor BOR-60 with doses of 8–16 × 1025 n/m2 and in the mixed spectrum neutron reactor SM-2 with doses of 3.7–5.5 × 1025 n/m2. The experimental data on the change Δϱ in electrical resistivity of DS-type copper alloys irradiated in the BOR-60 reactor show that irradiation to 7–10 dpa at T = 340–450°C causes a drop in electrical conductivity by not more than 20%. The obtained results show that in mixed-spectrum reactors the rate of Δϱ normalized to the dpa is about 20 times as high as in fast neutron reactors. The conclusion is made that the calculations performed for ITER must take into account the presence of appreciable fluxes of thermal neutrons in certain components of the reactor. The latter will play a decisive role in the drop in thermal conductivity of copper alloys in these components.

Effect of neutron dose and irradiation temperature on the mechanical properties and structure of dispersion strengthened copper alloys

This report is the first to present the data on the effect of neutron irradiation doses of 0.2 and 0.4 dpa at T irr ∼150°C and T irr ∼300°C on the mechanical properties of the GlidCopA125IG alloy in different metallurgical conditions (CR + annealed, HIP, as-extruded). The dose dependence of radiation strengthening for GlidCopA125IG alloy at T test = T irr = 150°C shows that strengthening increases with dose, up to Δσ y ∼ 100 MPa at 0.4 dpa. Simultaneously, the uniform elongation decreases with increasing dose. An important point is that all investigations on ODS copper alloys, regardless of the metallurgical state (CR + ann, HIP, as-extruded), revealed similar dose dependencies of strengthening and loss of ductility. Irradiation up to 0.4 dpa at 300°C results in a slight strengthening of about 30 MPa of the ODS copper alloys. In this case the tendency to embrittlement depends on the metallurgical state and orientation of the specimens.

The effect of rhenium on the radiation damage resistivity of Mo–Re alloys

Abstract The results of investigations of alloys in the Mo–Re system are presented with Re varying from 0.5 to 47%. Samples were irradiated in the SM-2 reactor up to doses of 1–5.5×10 25 n/m 2 ( E >0.1 MeV) at 100°C, 210°C, 260°C and 330°C and in the BOR-60 reactor to doses of 0.8–2.0×10 26 n/m 2 ( E >0.1 MeV) at 480°C, 550°C, 760°C and 800°C. Irradiation to high doses in the SM-2 and BOR-60 reactors results in pronounced embrittlement of Mo–Re alloys in the testing temperature range of 300–600°C. The study of the electrical conductivity of the alloys has shown that irradiation in SM-2 results in a linear increase of the electrical resistivity with increasing Re concentration. Based on the analysis of available data the tentative conclusion has been made, that during irradiation in a mixed-spectrum reactor the resonance reaction proceeds on Re giving rise to the accumulation of transmutants (Os) reducing the electrical conductivity of the alloys.

The effect of neutron dose, irradiation and testing temperature on mechanical properties of copper alloys

Abstract The paper presents the results of comparative investigations of radiation embrittlement of UHS–PH copper alloys of Cu–Ni–Be, Cu–Cr–Ni–Si type and the base Cu–Cr–Zr alloy after irradiation to 0.2 dpa at temperatures of 150°C and 300°C. The investigations undertaken and the analysis of changes in the mechanical properties of high-strength alloys of Cu–Ni–Be and Cu–Cr–Ni–Si irradiated to 0.2 dpa at 150°C and 300°C allowed for the conclusion that at low irradiation and testing temperatures alloys are prone to low-temperature embrittlement, which shows up in these alloys in the same way as in ITER base alloy. At elevated irradiation and testing temperatures the high-strength Cu–Ni–Be and Cu–Cr–Ni–Si alloys embrittle, and what is more, demonstrate, when irradiated, a low level of fracture stress (about twice as low as the initial material).

Effect of high-dose neutron irradiation on the mechanical properties and structure of copper alloys and Cu/SS joints for ITER applications

Abstract The base copper alloys Cu–Cs–Zr IG and GlidCopAl25 IG and Cu/SS joints manufactured in Russian Federation (RF), United States (US), Europe (EU) and Japan (JA) with the HIP method were irradiated up to 2 dpa at 200°C in SM-2 reactor. Tensile tests, shear tests, metallography and SEM investigations were performed. Mechanical test results on the base alloys and joints irradiated up to 2 dpa at 200°C indicate that the trends established at lower dose (0.3–0.4 dpa) tests are still valid at higher doses. The main effect of the irradiation dose increase can be considered as a shift of the low temperature embrittlement towards higher temperatures.

The effect of neutron irradiation on mechanical properties of Cu/SS joints for ITER applications

Abstract The paper presents the first results on the properties of Cu//SS-type joints irradiated in the SM-2 reactor up to a dose of 0.2 dpa at T irr =150°C and 300°C. The investigations performed demonstrated that the proposed HIP (RF) and (US) technology, as well as Explosive Bonding (US) holds promises and can be recommended for preparation of samples for subsequent irradiation. On the other hand, the investigation undertaken revealed the problem of 150°C embrittlement of joints observed for Lap Shear specimens GlidCop A125//316LN (US) manufactured by the HIP method.

High-temperature beryllium embrittlement

Abstract The neutron irradiation effect on the mechanical properties, swelling and fracture surface structure of various beryllium grades was studied in the BOR-60 reactor at 340 to 350°C up to a fluence of 7.2 × 10 21 n/cm 2 . At a mechanical testing temperature of 400°C there was observed a strong anisotropy of plastic beryllium deformation depending on the direction of sample cutting relative to the pressing direction. An increase of the testing temperature up to 700°C resulted in an abrupt embrittlement of all irradiated samples. In the most part of the surface structure the intercrystallite fracture along the grain boundaries was covered entirely with large pores, 1 to 4 μm in size. It was suggested that the increase rate of pore formation along the grain boundaries resulted from a high-temperature embrittlement under irradiation.

Effects of neutron irradiation on the properties of Cu-Mo dispersion strengthened alloy

Abstract Results of radiation resistance studies of the Cu-5Mo alloy are presented. Samples were irradiated in SM-2 reactor up to 1∗1025 n/m2 at Tirr∼100-450°C and BOR-60 reactor up to 1∗1026 n/m2 at 350-420°C. Studies of neutron irradiation influence on mechanical properties, swelling and electric resistance were carried out. Dispersion-strengthenend alloy Cu-Mo demonstrates rather high stability of mechanical properties under irradiation.