When under stress, metals may become susceptible to liquid metal embrittlement (LME). Different to most of corrosion mechanism, LME is usually not involving with electrochemical reactions. Liquid metal embrittlement (LME) is not being classified as SCC as well. However, the fracture appears to be brittle intergranular fracture in nature. Susceptible metals have sometimes been observed to crack almost instantaneously when wetted by certain molten metals. Instances of LME are often associated with welding, brazing, or soldering.
Like other forms of environmental cracking, LME is highly specific to the alloy and environment combinations. Typical of such combinations are listed in the following tables. It is generally accepted that most cases of LME arise from the effects of chemisorption of liquid–metal atoms and the consequent reduction of the tensile strength of interatomic bonds. The compounds form in the matrix of the alloy, for example, as grain-boundary intermetallic compound (IMC) is the cause of such embrittlement. Although no corrosion loss can be observed., it may cause rupture within seconds. The crack growth rate could be very high (up to 10 cm/s).
The occurrence and severity of the LME are governed by
- the particular solid–metal/liquid–metal combination;
- the temperature;
- the strain rate;
- the initial mechanical and metallurgical state of the solid metal.
| Susceptible Alloy | Molten metals | Examples |
| Carbon steel | Copper, cadmium and zinc. | Hot-dip galvanizing mild carbon steel during welding
long-time aging at 370~427oC Zinc and cadmium plated bolts at long-time aging or fire incident Weld cracking due to copper contamination: from cold forming tools or back-up bars Cracking caused by copper containing antiseize compounds; Improper brazing procedure can be caused by excessive diffusion into the parent metal of the molten brazing alloy, especially where the parent contains residual or applied stresses. |
| 300 Series SS | Zinc, Copper, lead, cadmium, aluminum | Galvanised steel,
zinc rich paint, over spray of IOZ paint. Contamination of Stainless steel with galvanised wire during heat treatment. Contamination of zinc from grinding. Welding of galvanised steel with stainless steel by remove zinc layer. Cadmium plated bolt
|
| Copper Alloys including copper brasses, bronzes and cupro-nickels | Mercury
lead, lead-tin solders, tin and sodium |
Broken manometers, thermometer etc
mercury salts (such as mercurous nitrate) will cause issue if it is reduced to metallic mercury |
| Nickel Alloy | Mercury
Lead Silver solder |
for Alloy 400 components even at room temperature,
Metallic Mercury for Alloy 200 at elevated temperature Traces of mercury have been reported to accelerate SCC of austenitic stainless steels in chloride solutions. Lead-containing lubricants or anti-galling compounds have reportedly caused cracking of Alloy 600 in nuclear applications. using silver-based braze fillers at temperatures well-below the annealing temperature of the base metal without annealing before the brazing |
| Aluminum Alloys | Mercury,
Tin, zinc. Gallium |
Mercury and mercury compounds are particular harmful for aluminium alloys,
Gallium is particularly aggressive to low and high strength aluminium alloys. |
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