Liquid Metal Attack

Description

Corrosive degradation of metals in the presence of certain liquid metals such as mercury, zinc, lead, cadmium. examples of liquid metal attack include: chemical dissolution. metal-to-metal alloying (i.e. amalgamation). embrittlement and cracking.

Prevention or Remedial Action

• selection of compatible materials.
• removal of liquid metal from environment.
• application of resistant surface coating or treatment to act as a barrier between metal and environment.
• chemical dissolution and amalgamation - see test methods for general corrosion and pitting.
• liquid metal embrittlement - see test methods for scc.

Standard Test Methods

• ASTM G129 - slow strain rate test for determination of environmentally assisted cracking.
• ASTM G-30 - practice for making and using U-bend SCC test specimens.
• ASTM G-38 - practice for making and using C-ring SCC test specimens.
• ASTM G-39 - practice for preparation and use of bent-beam SCC test specimens.

Evaluation for Liquid Metal Embrittlement (LME)

The evaluation of LME usually requires chemical or mechanical techniques to overcome the incubation period for cracking. In much the same way that a localized corrosion event is needed to initiate SCC, local chemical attack is usually a precursor for LME. Dynamically applied loads as in the slow strain rate test can be used to break normally protective surface films to allow intimate contact of the material surface and the liquid metal. Chemical agents can also be used to remove or breach this surface films and initiate localized attack so that the inherent susceptibility of the material can be determined. In some cases, surface treatments may be utilized to enhance resistance to LME. However, this should be conducted with extreme caution since damage to this surface layer may induce cracking.