Intermediate temperature embrittlement of copper alloys

Abstract

Copper and its alloys generally display a severe reduction in ductility between roughly 300°C and 600°C, a phenomenon variously called "intermediate temperature embrittlement" or "ductility trough behaviour". This review of the phenomenon begins by placing it in the wider context of the high-temperature fracture of metals, showing how its occurrence can be rationalized in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation. Data in the literature are reviewed to identify main causes and mechanisms for embrittlement, first for pure copper, and then for monophase and multiphase copper alloys. Coverage then turns to the "grain boundary embrittlement" phenomenon, caused by the intergranular segregation of even minute quantities of alloying additions or impurities, which appears to worsen dramatically the intermediate temperature embrittlement of copper alloys. Finally, metal-induced embrittlement, including in particular liquid metal embrittlement, is presented as a second mechanism leading to an exacerbation of the intermediate temperature embrittlement of copper and its alloys.

Grain Refinement of Deoxidized Copper

“…Known grain boundary embrittlers of copper are marked with unfilled symbols, and 'de-embrittlers' of copper are marked with filled square symbols and in bold (adapted from Ref. 13), including ambivalent character of phosphorus. of 0.05 pct, the grain size increased significantly for Mo, Sn, and Pb; slightly for In, Sb, and Se; and marginally for Bi; (iii) a further addition of solute to 0.1 pct, however, resulted in a decrease in grain size; and (iv) with a further addition of solute to 0.5 pct, the grain sizes decreased slightly for Te and Bi; showed stabilization for S; although they increased for Sn, Sb, and Pb with respect to the 0.1 pct addition, these were, still marginal for Mo, In, and Se.…”

“…One main issue is the grain boundary embrittlements of copper and its alloys caused by Bi, Te, S, Sn, O, Sb, Pb, Se, C, and in some cases P. [13][14][15] On the other hand, 'de-embrittling' elements, i.e., elements that enhance grain boundary cohesion include Zr, Mg, B, Y, Ce, La, Ca, Nb, Li, U, and to a lesser extent P and Ti (see Reference 13 for details). This has been marked in Figure 1.…”

“…[3]): 220 g castings, 30-mm diameter, and 35-mm height; known grain boundary 'embrittlers' of copper are marked with unfilled symbols, and 'de-embrittlers' of copper are marked with filled square symbols and in bold (adapted from Ref. [13]), including the ambivalent character of phosphorus. Reprinted with permission from Ref.…”

Impurity effects on the grain boundary cohesion in copper

“…Both the strain and chemical contributions to the work of dislocation emission generally become weaker with the increasing electronegativity from Mg to S. By combining these contributions together, we find, in agreement with experimental observations, that a strong segregation of S can reduce the work of grain boundary separation below the work of dislocation emission, thus embrittling Cu, while such an embrittlement cannot be produced by a P segregation because it lowers the energy barrier for dislocation emission relatively more than for work separation. DOI: 10.1103/PhysRevMaterials.1.070602Impurity-induced embrittlement accounts for many notorious cases of brittle failure of polycrystalline metals [1][2][3]. Bismuth-embrittled nickel and copper are well-known cases of such an embrittlement and, therefore, they have been extensively studied [1,[4][5][6].…”

“…However, no theory could explain the remarkable difference between the effects of P and S on the ductility of polycrystalline copper [7,8]. Segregated S at GBs is strongly detrimental and several ppm of residual S can remarkably embrittle copper [3,9,10]. However, the addition of about 50 wt ppm of the neighboring element P can cure the Cu embrittlement problem and recover the ductility of polycrystalline copper [8].…”