清华大学：《材料科学基础》课程教学资源（PPT课件讲稿）Chapter 5. 12 Interaction between

85.12 Interaction between Dis locat i on and point Defect 4丌 E=-p△V=-p-(R3-n3) 3 p=-(0x+oy+a2) Cottrell Atmosphere -VE=-gradE Strain aging By cottrell atmosphere model, we can explain the sharp yielding phenomenon

§5.12 Interaction between Dislocation and Point Defect By cottrell atmosphere model, we can explain the sharp yielding phenomenon. f E E p E p V p R r x y z grad ( ) 3 1 ( ) 3 4 3 3 = − = − = − + + = −  = − −        Cottrell Atmosphere Strain aging

Point defect Cottrell Atmosphere Compression Tensi

Point defect Cottrell Atmosphere

strain aging)BCC

(strain aging)－－BCC  

35.13 Multipl ication of dislocations I What's mul tipl ication and why is it needed? II. Key points of the mechan i sms of the mul tiplication 1. The dislocation does not lie entirely on the same slip plane

§5.13 Multiplication of dislocations ◆ Ⅰ.What’s multiplication and why is it needed? ◆ Ⅱ.Key points of the mechanisms of the multiplication. 1. The dislocation does not lie entirely on the same slip plane

2. Part of the dislocation segments can not move for either of the following reasons a. No applied stress b. The plane on which the segment would move is not allowed crystallographically c. There is strong obstacles around the segment

2. Part of the dislocation segments can not move for either of the following reasons. a. No applied stress b. The plane on which the segment would move is not allowed crystallographically. c. There is strong obstacles around the segment

E 2b%7 (b) E (c) (d)

l. Frank-Read mechanism or F-R source 1. F-R mechanism: L- shaped dislocation 2. F-R source d =2T sm2 cbdl-tbode T aGb aGb T=tbp tb Tb aGb When T≤ dislocation is in quasi-static equilibrium When t> eGb dislocation will spontaneously slip

◆ Ⅲ.Frank-Read mechanism or F-R source. 1. F-R mechanism: L- shaped dislocation. 2. F-R source.              G b b G b b T T b f r T b l b  =  = = = = = = 2 d d 2 d 2 sin When dislocation is in quasi-static equilibrium When dislocation will spontaneously slip ) 2 ( L Gb   ) 2 ( L Gb  

b tb D D E (a) (b) k b D D D D ; (d)

F-R Source Applied shear

Examples and Discussions

Examples and Discussions