Question

Materials/Edge Dislocation Problem:

3. Problem 3: (40 points An edge dislocation given by burgers vector, 01] on the (111) plane in an fcc crystal dissociates into two partial dislocations a) Provide the dislocation reaction for the above. Vectorially depict the three dislocations on a (111) plane b) Prove that the reaction is thermodynamically feasible c) The two partial dislocations can each be split into horizontal and vertical components. Each of the components are either, pure screw or edge dislocations. These components repulsively interact with each other while creating a stacking fault in-between them. Derive an equation which measures the net force per unit length (in N/m) between the two partial dislocations. Is this force attractive or repulsive? d) If the stacking fault energy per unit length is given as USE w (in J/m) where, USFE-stacking fault per unit area (in J/m2), derive an expression for the equilibrium stacking fault separation distance 'Wea', of the stacking fault. Use Poisson's ratio, u - 0.33

Answer 1

A/2 [1 0 1] = a/6 [2 11] + a/6 [T I 2] energy of perfect dislocation = G . b^2 = G . (a /2 < t o l >) energy of planetoids dislocation is less it is feasible z b = force acting on unit length of the dislocation b = burgers vesper t = line tension acting alang the length of the dislocation 2 theta = angle subtended at the center of the are z b s = 2 t sin theta 2 t theta = t s/r rightarrow z = t/r b = 0 . 5 G b/R T = 0 . 5 g b ^2/1 t = 0 5 g b^2