Classification of Defects 0 Dimensional Defects 2 Dimensional - PowerPoint PPT Presentation

31/10/2019 Crystal Defect 1. Vector repositioned (if necessary) to pass through origin. 2. Read off projections in terms of unit cell dimensions a 1 , a 2 , a 3 , or c 3. Adjust to smallest integer values 4. Enclose in square brackets, no commas [ uvtw ] 1 2 1 2 Classification of Defects 0 – Dimensional Defects 2 – Dimensional Defects  Point Defects  Plane Defects Vacancy Grain Boundary • • Interstitial Stacking Faults • • Substitution • 1 – Dimensional Defects 3 – Dimensional Defects  Extended Defects  Line Defects Pores • Edge Dislocation • Cracks Screw Dislocation • • 3 4 3 4 1

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31/10/2019 BURGERS VECTOR BURGERS VECTOR The magnitude and the direction of the displacement are defined by a vector, called the Burgers Vector . So, we have to move an extra step to return to P, in order to In figure (a), starting from the point P , we go up by 6 steps, then move close the Burgers circuit. towards right by 5 steps, move down by 6 steps and finally move towards left by 5 steps to reach the starting point P . the Burgers circuit The magnitude and the direction of the step defines the Burgers gets closed. Vector (BV). When the same operation is performed on the defect crystal (figure (b)) we end up at Q instead of the starting point. BV = = b   QP The Burgers Vector is perpendicular to the edge dislocation line. 45 46 45 46 47 48 47 48 12

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