LINE DEFECTS Edge Dislocation Unslipped Burgers vector slipped

LINE DEFECTS Edge Dislocation Un-slipped Burgers vector slipped Dislocation “core” Adapted from “Engineering Materials 1” by Ashby and Jones Dislocation Line Ø A dislocation is define by its line and its displacement vector known as Burgers vector. Ø Dislocation line is the boundary between the slipped and un-slipped areas. Ø The dislocation line is perpendicular to the Burgers vector in edge dislocations.

LINE DEFECTS Screw Dislocation displace cut Dislocation line Adapted from “Engineering Materials 1” by Ashby and Jones Ø The dislocation line is parallel to the Burgers vector in screw dislocations

LINE DEFECTS Mixed Dislocation b b Adapted from Figure 4. 5 of Callister Ø The character of a dislocation may change along its line, however the direction of the Burgers vector remains the same.

Observing Dislocations Transmission Electron Microscopy (TEM) Etch Pitting High Resolution TEM Copper Other techniques: - X-ray - Field Ion Microscopy

AREA (PLANAR) DEFECTS: GRAIN BOUNDARIES Grain boundaries: • are boundaries between crystals. • have a change in crystal orientation across them. • form by many processes including solidification, deposition and recrystallization. Metal Ingot Schematic Adapted from Fig. 4. 7, Callister 6 e. ~ 8 cm heat flow Adapted from Fig. 4. 10, Callister 6 e. (Fig. 4. 10 is from Metals Handbook, Vol. 9, 9 th edition, Metallography and Microstructures, Am. Society for Metals, Metals Park, OH, 1985. )

OBSERVING GRAIN BOUNDARIES Optical Microscopy HRTEM Low-angle boundary Nanocrystalline Ni-15%Fe alloy Adapted from Callister, Fig. 4 -12