Time-Dependent Failure Mechanisms of Metals: The Role of Bifilms in Precipitation Cleavage

This account is an exploration of concepts exploring the widespread damage to liquid metals caused by poor current liquid metal handling and casting technology. The defects introduced in the liquid state are suggested to affect many properties of our engineering metals, especially tensile elongation and Charpy toughness, but also time-dependent degradation processes, which can result in failure by fracture, and which can be significantly aided by hydrogen, leading to hydrogen embrittlement (HE), and invasive corrosion, leading to stress corrosion cracking (SCC). The new phenomenon of ‘precipitation cleavage’ is introduced, explaining the sensitization of alloys by certain heat treatments. Direct visual evidence for precipitation cleavage is provided by the previously unexplained phenomenon of ‘fisheyes’ observed frequently on the fracture surfaces of steels, and more recently also in light alloys.