Liquid metal embrittlement

Mechanical behavior Liquid metal embrittlement is characterized by the reduction in the threshold stress intensity, true fracture stress or in the strain to fracture when tested in the presence of liquid metals as compared to that obtained in tests. The reduction in fracture strain is generally temperature dependent and a “ductility trough” is observed as the test temperature is decreased. There should be limited mutual solubilities for the metal couple to cause embrittlement. Excess solubility makes sharp crack propagation difficult, but no solubility condition prevents wetting of the solid surfaces by liquid metal and prevents LME. The presence of an oxide layer on the solid metal surface also prevents good contact between the two metals and stops LME. The chemical compositions of the solid and liquid metals affect the severity of embrittlement. The addition of third elements to the liquid metal may increase or decrease the embrittlement and alter the temperature region over which embrittlement is seen. Metal combinations which form intermetallic compounds do not cause LME. There are a wide variety of LME couples. == Mechanisms ==

Many theories have been proposed for LME. and Glikman says that absorption of the liquid metal on the solid metal induces dissolution and inward diffusion. Under stress, these processes lead to crack nucleation and propagation. • The brittle fracture theory of Stoloff and Johnson, Westwood and Kamdar proposed that the adsorption of the liquid metal atoms at the crack tip weakens inter-atomic bonds and propagates the crack. • Gordon postulated a model based on diffusion-penetration of liquid metal atoms to nucleate cracks which, under stress, grow to cause failure. • The ductile failure model of Lynch and Popovich predicted that adsorption of the liquid metal leads to the weakening of atomic bonds and nucleation of dislocations, which move under stress, pile up and work harden the solid. Also, dissolution helps in the nucleation of voids which grow under stress and cause ductile failure. All of these models, with the exception of Robertson, utilize the concept of an adsorption-induced surface energy lowering of the solid metal as the central cause of LME. They have succeeded in predicting many of the phenomenological observations. However, quantitative prediction of LME is still elusive. ==Mercury embrittlement==

The most common liquid metal to cause embrittlement is mercury, as it is a common contaminant in the processing of hydrocarbons in petroleum reservoirs. The embrittling effects of mercury were first recognized by Pliny the Elder circa 78 AD. Mercury spills present an especially significant danger for aeroplanes. The aluminium-zinc-magnesium-copper alloy DTD 5050B is especially susceptible. The Al-Cu alloy DTD 5020A is less susceptible. Spilled elemental mercury can be immobilized and made relatively harmless by silver nitrate. On 1 January 2004, the Moomba, South Australia, natural gas processing plant operated by Santos suffered a major fire. The gas release that led to the fire was caused by the failure of a heat exchanger (cold box) inlet nozzle in the liquids recovery plant. The failure of the inlet nozzle was due to liquid metal embrittlement of the train B aluminium cold box by elemental mercury. ==Popular culture==

Liquid metal embrittlement plays a central role in the novel Killer Instinct by Joseph Finder. In the film Big Hero 6, Honey Lemon, voiced by Genesis Rodriguez, uses liquid metal embrittlement in her lab. == See also ==