Penetration of liquid metals into solid metals and liquid metal embrittlement

For some solid metal–liquid metal couples that exhibit liquid metal embrittlement, penetration of the embrittling liquid metal along grain boundaries of the solid metal is observed. Penetration speed of liquid gallium into aluminum and that of mercury into silver and copper were measured by using thin evaporated films. The degree of embrittlement induced by the liquid metal was estimated by tensile tests. The tensile specimens were kept in contact with the liquid metal for various times of exposure, and then the embrittler was removed before the test. When the exposure time is short, no sign of embrittlement is observed. As the exposure time increases further, the brittle fracture surface area increases with logarithm of the exposure time. The results imply the existence of an incubation period, which is inversely proportional to the penetration speed of embrittling liquid metal.