Intergranular fracture is usually the most easily recognizable mode of fracture, but determining the cause may be quite difficult. Although fractography identifies the presence of intergranular fracture, a correlation of both fractographic and metallographic features should be obtained to aid in identifying the mechanism responsible.

Case histories of failure analyses in which intergranular fractures were observed and were attributed to a variety of mechanisms are presented and include (1) liquid-metal embrittlement of an AISI 1070 rod caused by copper pickup during processing, (2) liquid-metal embrittlement of a low-carbon steel caused by lithium in service, (3) liquid-metal embrittlement of a platinum and platinum-rhodium thermocouple caused by a low-melting platinum-silicon eutectic that formed in service, (4) fracture of a steel-strand wire-rope caused by an area of untempered martensite, (5) “rock candy” brittle fracture of a steel casting caused by the presence of aluminum nitride at the solidification grain boundaries, and (6) brittle fracture of heat-treated bolts manufactured from columbium-treated fine-grain AISI 1541 steel caused by the presence of a columbium film at prior-austenite grain boundaries.

The investigative techniques used included light microscopy, scanning electron microscopy, energy-dispersive spectroscopy, electron diffraction, and secondary-ion mass spectroscopy.