Chapter 3 dislocation

1. Chapter 3 dislocation The yield strength of a perfect crystal •  = maxsin( • = G = G •  = max • max =

2. Whiskers defect-free crystal  = G/30 for aluminum y = 9 x 108 N/m ideal strength 7.8 x 105 N/m real strength

3. The edge dislocation Slip by an edge dislocation motion line defect ; an extra half plane

4. Peierls force Shear stress is applied. Dislocation move Peierls – Nabarro: The friction for the movement of dislocation: f = G exp[ G : shear modulus  : Poisson’s ratio Real strength

5. f = G exp[ w : dislocation width

6. Climb of edge dislocation Glide : conservation motion Climb : non-conservative motion

8. Topographic considerations Burgers circuit

9. Motion of edge dislocation containing jogs The parts of jogs can’t move due to its components do not lie on the slip plane.

11. The dislocations in the 70% cold rolled Fe-19%Cr alloy

12. Edge dislocation Screw dislocation Mixed dislocation

13. Positive dislocation and negative dislocation phenomenon of recovery

14. Dislocation density  m/m3, 1/m2 Annealed metals :  = 109 – 1011 m/m3 Heavily cold worked materials :  = 1014 -1016 m/m3 The relationship between dislocation movement and strain and

15. BCC降伏点降下現象(yield drop)的説明 discontinuous yielding v：dislocation average speed ρ：dislocation density Johnston and Gilman : from etching pits movement: ｍ値:　因材料而異之定数 半導体：１〜２、LiF結晶：約25、Fe-Si 合金：約40、炭鋼：10 〜30、純鉄：5〜10。

16. 明顕的降伏点降下現象（yield drop, discontinuous yielding）、一般在bcc 結晶中常見、fcc或hcp結晶中不常観察到。 由bcc、及fcc・hcp結晶之塑性特徴、可由以下幾点加以説明。 bcc： 運動差排密度 ρ 大、差排的運動速度 v小（dislocation movement rate controlled process） fcc, hcp： ρ 小、v大（dislocation multiplication rate controlled process） 此為、bcc結晶中之交差滑移容易、可期待2重交差滑移(double cross slip)之差排源的活化、螺旋差排之Peierls forceが大、移動困難 而、fcc結晶之交差滑移困難的場合多、Peierls也相対的小。