Dislocation cannot end abruptly in a crystal: Grain boundaries

Dislocation cannot end abruptly in a crystal: Grain boundaries

[@veerendrachabbi7119]

Sir, I truly appreciate your dedication and sincerity in making all these videos. Thankyou seems a very small thing i can say. Thankyou a lots sir.

[@pranav9339]

Truly magnificent professor, you're presentation is indeed awesome.! You should actually consider writing and publishing your own book for this course in your own natural presentation. I'm sure it would contribute a lot to the global engineering community. Thank you for your valuable time.

[@shubhanshimishra3425]

Thank You sir

[@sanahurain605]

NIce video

[@adarsh7307]

nice

[@al-hasanmansuri1678]

Colloquially what we say 'A PURE CRYSTAL' is that a single crystal?

[@rajeshprasadlectures]

There is a difference between 'pure crystal" and 'single crystal. Purity refers to chemical composition. 'Single crystal" refers to structure. Thus if I have pure crystals of Cu it means there is no other chemical element present. A single crystal requires the absence of grain boundaries. A pure crystal of Cu still may not be a single crystal. It may be polycrystalline, i.e., different regions of the crystals have their FCC unit cells oriented differently. These differently oriented crystals are separated by grain boundaries. On the other hand, I may have an alloy of Cu with 5% Ni which is still single crystal if it has no grain boundaries. To summarise, you can have pure single crystal, or pure polycrystal, or impure single crystal, or impure polycrystal.

[@RAMESHKUMAR-tb5kt]

Dear sir g why grain boundaries are formed??? I mean at micro(atomic level) what kind of state atoms have at grain boundaries???.....

[@introductiontomaterialsscience]

You can think of grains forming in a liquid during solidificitation. Different grains start as a nuclei in different parts of liquid. Because of independent nucleation events their orientations are arbitrary. After growth they meet along some surface across which the orientation changes. These surfaces act as grain boundaries. Atoms close to the boundary do not fit in either grain and so their is some disorder in a thin layer of atoms along the grain boundary.

[@saicharan9174]

sir i had a doubt whether grain boundary seperates the same planes or different different planes?????i mean grain boundary is a boundary where planes changes its orientation or is a boundary where different different planes meet ??????

[@rajeshprasadlectures]

Both are true. A grain boundary separates two grains. In a grain on either side of the grain boundary planes with different orientations (different Miller indices) meet the boundary. But if you consider a plane with given Miller Indices, it will have a different orientation in the two grains.

[@sarojinisahu6654]

Sir, dislocation cannot cross a grain boundry and finer grain structure means lots of grain boundaries but plastic deformation which is caused by slip ( movement of dislocation) is more favourable with fine grains..what is the reason?