DBTT is observed postly in BCC structured metals but not in FCC

[abhinandan admuthe]

Expecting answers from your side.....

[devil minds]

Ductile to Brittle Transition Temperature
The ductile-brittle transition is exhibited in bcc metals, such as low
carbon steel, which
become brittle at low temperature or at very high strain rates. FCC
metals, however,
generally remain ductile at low temperatures.
In metals, plastic deformation at room temperature occurs by
dislocation motion. The
stress required to move a dislocation depends on the atomic bonding,
crystal structure,
and obstacles such as solute atoms, grain boundaries, precipitate
particles and other
dislocations. If the stress required to move the dislocation is too
high, the metal will fail
instead by the propagation of cracks and the failure will be brittle.
Thus, either plastic flow (ductile failure) or crack propagation
(brittle failure) will occur,
depending on which process requires the smaller applied stress.
In fcc metals, the flow stress, i.e. the force required to move
dislocations, is not strongly
temperature dependent. Therefore, dislocation movement remains high
even at low
temperatures and the material remains relatively ductile.
In contrast to fcc metal crystals, the yield stress or critical
resolved shear stress of bcc
single crystals is markedly temperature dependent, in particular at
low temperatures. The
temperature sensitivity of the yield stress of bcc crystals has been
attributed to the
presence of interstitial impurities on the one hand, and to a
temperature dependent
Peierls-Nabarro force on the other. However, the crack propagation
stress is relatively
independent of temperature. Thus the mode of failure changes from
plastic flow at high
temperature to brittle fracture at low temperature.
On Jan 14, 6:10 pm, abhinandan admuthe <abhinandanbadmu...@gmail.com>
wrote: