Environmental Engineering Reference
In-Depth Information
ated zinc with grain size. In this case, the fracture is nucleation-controlled in
region I but propagation-controlled in region II. The grain size dependence of
LME is indicative of a reduction in cohesive strength of the material rather than
an effect of the penetration or dissolution of liquid into the grain boundary.
Effect of Temperature
LME takes place at temperatures above the melting point of the liquid metal
component, except for the few cases of embrittlement caused by the vapor phase
(SMIE). In the vicinity of the melting point of the liquid metal, LME is relatively
temperature-insensitive. At higher temperatures, a brittle-to-ductile transition oc-
curs in many systems over a temperature range and the ductility is restored (Fig.
7.7). The fracture stress in air is regained at and above the transition temperature.
The effect is generally ascribed to the increased ductility of solid with increase
in temperature.
The brittle-to-ductile transition temperature is dependent on the presence of
notch, grain size, and strain rate. The transition temperature is raised in the pres-
ence of notches. An increase in strain rate and a decrease in grain size increases
the transition temperature.
Effect of Strain Rate
In addition to the effect on brittle-to-ductile transition temperature, as mentioned
above, the strain rate of test may be an important factor for the occurrence of
LME. It has been reported [4] that in precracked aluminum single crystals tested
in liquid gallium at the crack tip, embrittlement was not observed at a slow strain
Figure 7.7
Temperature dependence of strain at fracture for (a) unamalgamated and
(b) amalgamated zinc single crystals of approx. 1 mm diameter [8].
