The discussion of liquid-metal embrittlement involving fasteners continues.

A metallurgical investigation followed and revealed the presence of a tin-rich phase (Figs. 5-6), which was confirmed under the scanning electron microscope to be LME with a brittle intergranular fracture mode (Fig. 7). The tin was found at the grain boundaries – both those already exposed by fracture and internally that were not opened. EDS analysis was used to confirm the presence of tin-rich areas.

Liquid-metal embrittlement is one of the least-expected failure modes experienced by products in service applications. When it occurs, it is often catastrophic. However, it is correctable by proper matching of materials with their environment as well as controlling the stress state and hardness of the material.

References

1. de Rosset, William S., Use of Liquid Metal Embrittlement (LME) for Controlled Fracture, Army Research Laboratory, ARL-TR-4976, September 2009.

2. C. J. McMahon, Jr., Brittle Fracture of Grain Boundaries, Interface Science 12, 141- 146, 2004.

3. Bogner, B., G. Rorvik, and L. Marken, Bolt Failures – Case Histories from the Norwegian Petroleum Industry, Microscopy and Microanalysis, Volume 11 Supplement S02, August 2005.

4. Wikipedia (www.wikipedia.com)

5. Kolman, D. G., Environmentally Induced Crackng, Liquid Metal Embrittlement, ASM Harndbook, Volume 13A, Corrosion: Fundamentals, Testing and Protection, ASM International, 2003., pp 381  392.

6. ATRONA Test Labs, Inc. (www.atrona.com), with permission.