Question

Biomaterials question: Biomedical Engineering

Would a perfect single-crystal metal (i.e. no defects) be able to deform plastically? Please explain using your knowledge of crystal structure, point, line, and plane defects.   

Answer 1

As we know that

Plastic deformation in a single crystal:

In a single crystal plastic deformation is accomplished by the process called slip and sometime by twinning

Then,

1)

The extent of slip depends on many factor s including external load and the corresponding value of shear stress produced by it,the geometry of crystal structure and orientation of active slip planes with the direction and shearing stress generated.

Then,

Schmid first recognized that single crystal at different orientation but of same material require different stresses to produce slip.

Then,

2)

Second important mechanism of plastic deformation is twinning. It results when a portion of crystal takes up orientation that is related to the orientation of rest of the entwined lattice in a definite symmetrical way.

Therefore,

The twined potion of the crystal is a mirror image of parent crystal.

So,

The lattice straines involved in twinning are small

Thus, resulting in very small gross plastic deformation.