27.04.2016 Views

Callister - An introduction - 8th edition

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

104 • Chapter 4 / Imperfections in Solids<br />

b Figure 4.8 Demonstration of how a tilt boundary<br />

having an angle of misorientation results from an<br />

alignment of edge dislocations.<br />

<br />

within and across the boundary are present. Furthermore, the density of a polycrystalline<br />

specimen is virtually identical to that of a single crystal of the same material.<br />

Phase Boundaries<br />

Phase boundaries exist in multiphase materials (Section 9.3), wherein a different<br />

phase exists on each side of the boundary; furthermore, each of the constituent phases<br />

has its own distinctive physical and/or chemical characteristics. As we shall see in<br />

subsequent chapters, phase boundaries play an important role in determining the<br />

mechanical characteristics of some multiphase metal alloys.<br />

Twin Boundaries<br />

A twin boundary is a special type of grain boundary across which there is a specific<br />

mirror lattice symmetry; that is, atoms on one side of the boundary are located in<br />

mirror-image positions of the atoms on the other side (Figure 4.9). The region of<br />

Twin plane (boundary) Figure 4.9 Schematic diagram<br />

showing a twin plane or boundary<br />

and the adjacent atom positions<br />

(colored circles).

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!