Bismuth induced embrittlement of a copper substrate
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Embrittlement of polycrystalline Cu by a liquid metal embitter species, such as Bi, is a well-documented phenomenon that is still relatively poorly understood. It has been shown previously that copper suffers from a reduction in ductility at intermediate temperatures with respect to its melting point and an increase at high temperatures below its melting point. This ductility trough is commonly referred to as intermediate temperature embrittlement (ITE). Further reduction in ductility is observed in the presence of a known embrittler by mechanisms such as grain boundary embrittlement (GBE), solid metal embrittlement (SME), and liquid metal embrittlement (LME). All of these effects act synergistically along with an applied load to cause intergranular fracture and ultimately material failure. Finite element analysis (FEA) was used to begin development of an empirical model to accurately predict failure of Cu as a function of temperature, exposure time, Bi concentration, and applied load. The grain structure of Cu was modeled using a modified 2D Voronoi diagram from experimental Cu micrographs obtained using a scanning electron microscope (SEM). Experimental load-displacement curves of Cu with Bi deposited on the surface at various temperatures were used to calibrate a traction-separation to predict the embrittlement behavior of the copper-bismuth system.
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