Concerning liquid metal embrittlement, particularly of zinc monocrystals by mercury

Abstract

The Obreimov—Gilman cleavage technique has been used to study, in a quantitative manner, the effects of a mercury environment on the cleavage fracture energy of high purity zinc monocrystals. The experimental observations support the view that the total energy involved in the propagation of a crack, Φ, can be conveniently represented by the relation Φ = η^• ρ ^• γ₀, where η is an environmental variable—-the coefficient of embrittlement—-which relates the energy required to separate atoms at the crack tip in the presence and absence of an embrittling phase, ρ is a dimensionless variable dependent upon the degree of plastic relaxation at the crack tip and independent of η, and γ₀ is the true surface energy of the fracture plane. In this work, γ_0Zn(77°K) was determined to be 90 ± 10 ergs/cm², γ_0Zn(29°K) to be 87 ± 5 ergs/cm² and ^η _Zn-Hg(298°) to be 0•61 ± 0•12.

On the basis of available experimental evidence concerning embrittlement by liquid metals, a new mechanism for this phenomenon is considered. This involves a localized reduction in cohesion introduced by the strain-activated chemisorption of liquid-metal atoms (i) at sites of high dislocation density, facilitating crack initiation, and (ii) at the tip of an initiated crack, facilitating its propagation.