Download presentation

Presentation is loading. Please wait.

Published byLea Letcher Modified over 2 years ago

1
Dislocation: dynamics, interactions and plasticity Slip systems in bcc/fcc/hcp metals Dislocation dynamics: cross-slip, climb Interaction of dislocations Intersection of dislocations

2
Edge/screw/mixed dislocations? Screw: Burgers vector parallel to the dislocation line. Edge: Burgers vector normal to the dislocation line.

3
Dislocation dynamics EdgeScrew Slip Direction|| to b|| to b between line and b || Line movement rel. to b|| How can disloc. leave slip planeclimb cross-slip n=( ) n=(111) b u b=n 1 xn 2 = (111)x ( ) = Climb: diffusion controlled. Important mechanism in creep.

4
Slip systems in crystals BCC FCC HCP {110} {211} {321} {0001} (10-10) (10-11) {111} Fe, Mo, W, brass Fe, Mo, W, Na Fe, K

5
b Superdislocation and partial dislocations Superdislocations in ordered material are connected by APB b Motio n of partial s Separation of partials Partial Dislocations b = b 1 + b 2 If energy is favorable, Gb 2 > Gb 1 2 + Gb 2 2 then partial dislocation form. ( Ga 2 /2 > Ga 2 /3)

6
Sessile dislocation in fcc n=(001) motion b Unless lock (sessile dislocation) is removed, dislocation on same plane cannot move past. n motion Lormer-Cottrell lockLormer lock

7
Sessile dislocation in bcc [001] is not a close-packed direction -> brittle fracture

8
Edge dislocation stress field y=x y=–x

9
Edge dislocations interaction edges dislocations with identical b X=Y repulsive attractive Stable at X=0 for identical b; Stable at X=Y for opposite b.

11
Edge dislocations interaction (general case) For an edge dislocations

12
Screw dislocations interaction Example: two attracting screws u (1) = (001) =u (2) b (1) = (001)b = –b (2) b1b1 radial force b1b1 r 1 2

13
Edge-Edge Interactions: creates edge jogs Dislocation 1 got a “jog” in direction of b 2e of the other dislocation; thus, it got longer. Extra atoms in half-plane increases length. This dislocation got a jog in direction of b 1e. after b 1e b 2e before b 1e b 2e **Dislocations each acquire a jog equal to the component of the other dislocation’s Burger’s vector that is normal to its own slip plane.

14
Dislocation intersection Interaction of two edges with parallel b Two screw kinks (screw) Edge jog on the edge Edge kink on the screw Edge jogs on screws

Similar presentations

Presentation is loading. Please wait....

OK

DISLOCATIONS Edge dislocation Screw dislocation.

DISLOCATIONS Edge dislocation Screw dislocation.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google