Low-temperature radiation embrittlement of copper alloys

Abstract

The effect of low-temperature (Tin less than 0.3 Tmelt) 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°C to doses of 0.6 to 5 dpa. Irradiation at temperatures 450°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 5100°C for doses above -0.01 to 0.1 dpa. On the other hand, irradiation at temperatures above 150°C causes only moderate embrittlement for doses up to -5 dpa. It is recommended that the minimum operating temperature for copper alloys intended for structural applications in fusion energy systems should be 15OoC, unless uniform elongations 4 % can be accomodated in the design.Key words: yield strength, uniform elongation, total elongation, radiation hardening corresponding author: S.J. Zinkle, tel. 423-576-7220, fax 423-574-0641 , email zinklesj@ornl.gov "The submitted manuscript has been authored by a contractor of the U.S. government under con-NO. DE-ACOS-960R22464. Accordingly, the US. Government retains a nonexclusive, royalty-fiee license to publish or reproduce the published fonn of this contribution, or allow others to do SO, for US. Government purposes." 2The use of copper alloys as a structural material for the ITER first wail and divertor poses befare materials scientists a large variety of challengmg problems. In many respects these problems arise fiom a lack of knowledge about the mechanical properties of copper alloys uradiated at ITER relevant conditions (50 to 350'C, doses up to -10 dpa). Previous work on pure copper [ 1,2] and copper alloys [3-91 has shown that sigruficant radiation and loss of ductility occurs m these materials following neutron irradiation at temperatures below 250'C. These studies suggest that low-temperature irradiation to doses as low as -0.1 dpa may cause substantial embrittlement of copper alloys. However, the data base on precipitation-hardened (PH) and dispersion strengthened @S) copper alloys at irradiation temperatures below 250'C is very limited. There are only a few known studies of the tensile properties of these materiais at damage levels >1 dpa at irradiation temperatures <200'C, where radiation hardening and embrittlement effects are most pronounced [3-6,8]. The present study summarizes recent results obtained on copper and copper alloys irradiated at 80-2OO' C to doses between 0.6 and 5 dpa. These data represent a subset of a collaborative llTadiation program that investigated the electrical and mechanical properties of copper and copper alloys irradiated at temperatures between 80 and 400'C and doses of 0.6 to 5 dpa [3]. Experimental ProcedureSheet tensile specimens h m copper (Russian Federation (RF) Cu, 99.97% purity and A.D.Cu-Mo), and a PH copper alloy (Cu-Cr-Zr) were llTad...

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“…At temperatures greater than 150 8C, PH and DS copper alloys remain ductile, with irradiated elongations in the range of 50 Á/90% of the unirradiated values [3]. However, the Joule losses in the centerpost would be elevated due to the increase in electrical resistivity with temperature.…”

“…However, the Joule losses in the centerpost would be elevated due to the increase in electrical resistivity with temperature. The increase in electrical resistivity for OFHC Cu, Glidcop AL-15, and CuCrZr with temperature is Fracture toughness Drops markedly with temperature between 25 and 250 8C [12] Drops slightly with temperature between 25 and 250 8C [12] Better than Glidcop AL-15 before and after irradiation [7] Embrittlement Drop in uniform elongation to 0.1 Á/1% above 0.01 dpa [3] Drop in uniform elongation to 0. particles would tend to redistribute during the melting process [7] Compatible with laser forming technique if the material can be properly heat-treated either during or after the deposition and shaping process [7] shown in Fig. 1.…”

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

“…In general, no appreciable difference in the yield strength increase (Aay) was observed for doses of 0.5 to 5 dpa at these irradiation temperatures, indicating that the radiation hardening had reached a saturation condition already at a dose of 0.5 dpa. By comparison with previously published studies on copper and copper alloys, it may be concluded that hardening generally approaches saturation at Ti,<150"C for doses above 0.1 dpa [ 1,7,9,12]. The one exception to this dose-independent behavior was cold-worked copper, which 6 reached a maximum strength of -450 MPa at a dose of -1 dpa and then decreased to -300 MPa at 4.5 dpa.…”

“…The yield strength of annealed copper irradiated at -100°C in an unshielded Channel 4 position was typically -50 MPa higher than annealed copper specimens irradiated in a Cd-shielded position [9]. However, the yield strength of cold-worked copper and DS copper alloys was similar in Cd-shielded and unshielded positions.…”

“…On the other hand, the value of the o , , increase was approximately the same for all materials and amounted to -150 to 200 MPa. The low-temperature radiation hardening data are summatized in a companion paper in these proceedings [9]. Figs.…”