Environmental Engineering Reference
In-Depth Information
This model suffers from the simple fact that a majority of the embrittlement
complex is mutually insoluble and it is unlikely that the simple application of
stress would change the solubility drastically. The embrittlement process also in
most cases is instantaneous and not influenced by time-dependent kinetic process.
According to this model, higher dissolution would be expected at a higher temper-
ature with a concurrent increase in embrittlement, but the practical evidences are
to the contrary; a brittle-to-ductile transition is encountered with an increase in
temperature in a number of systems.
Adsorption-Induced Reduction in Tensile Cohesion/Shear
Strength Model
The tensile decohesion model [8] treats the liquid metal embrittlement as a special
case of brittle fracture that is normally encountered in metals at low temperatures
in inert environments. The reduction of the shear strength model has been ex-
tended to explain the occurrence of ductile fracture in LME. Both of these models
are based on chemisorption of the embrittling species at the crack tip or at the
sites of stress concentration at the surface of the solid metal, bringing about a
localized reduction in the strength of the atomic bonds.
The situation at the crack tip has been schematically represented in Fig. 7.11.
The bond A-A
0
constitutes the crack tip and B is the liquid metal atom.
σ
repre-
sents the largest tensile fracture stress and
τ
the largest shear stress on the most
Figure 7.11
Schematic representation of the displacement of atoms at the crack tip.
(After Kamdar [8].)
