... voids are therefore inevitable, so that the structure of grain boundaries is essentially irregular. The crystal boundary atoms thus occupy positions of higher energy than those within the body of the crystal, and hence tend to undergo certain changes more readily. Metallic bonding continues through the grain bonding holding the mass together but because the bond lengths are under strain, stretched etc., the grain boundary is an area of high energy and a source of weakness where fracture might occur. It is possible for grain boundaries to be detected by etching the metal with an acid which attacks the boundary more easily. Defects In Metal Structures However carefully prepared and purified a metal may be, its crystalline structure does not consist of perfect arrays of atoms with all lattice sites occupied. Structural defects may be present in the crystal space lattice and these can be classified as either point defects or line defects. The commonest ...

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