Time-dependent interfacial failure in metallic alloys

Intermediate temperature embrittlement of copper alloys

“…There is a dependence of the embrittlement phenomenon on the prior time-temperature history of the material: this is simply related to the need for the embrittling species to migrate to the grain boundary or other site of fracture initiation for it to have an effect 8,199,203,[206][207][208][209][210][211] . Because decreasing temperature tends to increase the segregation driving force and decrease the segregation rate (which is generally limited by the rate of diffusion of atoms, either in the bulk or along grain boundaries), segregation effects are most visible in a certain intermediate range of temperatures.…”

“…Figure 14 represents a partial view of the periodic table of elements where copper is highlighted together with the position of its stronger, well-established, embrittling segregants. Note that oxygen counts among embrittling species 109,158,209,251,252 . This has the important consequence that copper and its alloys can be embrittled by interaction with the atmosphere; evidence of this can be found in Fig.…”

“…Given time to diffuse, therefore, the embrittling species may (further) lower the grain boundary cohesion and drive crack propagation, ending in fracture (indeed, a priori one would expect species that lower the local modulus, and hence the local bond strength, to migrate to a stressed region). This phenomenon is called "dynamic embrittlement", defined as fracture resulting from the stress-induced diffusion of an embrittler to the tip of an intergranular crack, reducing the strength of the grain boundary and promoting intergranular fracture 130,131,208,209,263,[311][312][313][314][315][316][317] ; see Ref. 318 for a recent review.…”

“…There is a dependence of the embrittlement phenomenon on the prior time-temperature history of the material: this is simply related to the need for the embrittling species to migrate to the grain boundary or other site of fracture initiation for it to have an effect. 8,199,203,[206][207][208][209][210][211] Because decreasing temperature tends to increase the segregation driving force and decrease the segregation rate (which is generally limited by the rate of diffusion of atoms, either in the bulk or along grain boundaries), segregation effects are most visible in a certain intermediate range of temperatures. It was thus found in one semi-quantitative study of copper-nickel-tin alloys that impurity-associated embrittlement can result from prior exposure to temperatures above the temperature of tensile testing: the dependence of embrittlement on annealing time and temperature showed the classical 'nose' shape on a TTT diagram.…”

“…Embrittling elements are many in copper alloys. These include: Bi, 10,21,146,214,216, Te, 10,21,244,245 S, 10,21,106,130,143,178,186,[246][247][248][249][250] Sn, 11,21,200,206,208 O, 109,158,209,251,252 Sb, 21,200,218,233,251,[253][254][255][256][257][258] Pb, 10,21,259 and Se 10,21,245 as well as C and, in some but not all instances, P. 21,145,174 Gavin ranks their potency in the order of (most to least potent) Bi, Te, Pb, Se, S. 10 Putting together data from the literature, the ductility trough of copper and its alloys indeed wide...…”