材料科学基础第04章3

1、材料科学基础Fundamental of MaterialsProf: Tian Min Bo Tel: 62795426 ，62772851 E-mail: Department of Material Science and EngineeringTsinghua University. Beijing 100084Lesson fourteen4.4 Rotation of Crystal during Slip.The cause of rotation: Due to constraints, or boundary conditions, imposed on the crysta

2、l.The rule of rotation : 1) axis of rotation 2) During slip, the S.D. tends to approach to loading direction in tension. During slip, the S.P. tends to approach to compression plane in compression.FFFFFFFF.The consequence of rotation :1. Change in length of the specimenIn tensionIn compression Geome

3、trical softening in tension Schmids law at the onset of slip: 2. Change in orientation Orientation change and multislipExample: Given: a FCC crystal held in tension Determine: 1. Single slip system 2. Rule of rotation 3. and orientation at the onset of duplex of slip 4. Rule of rotation during duple

4、x slip 5. Final orientation, i.e. the state positionslip system: locus: F tend to , Solution: stable: 4.5 Surface Morphology of Crystal After Slip The following deformation marks can be seen on the surface of the crystal after slip.Slip lines: the steps formed on surface due to slip.Slip bands.Defor

5、mation band formed due to inhomogeneous rotation.Kink bands4.6 Strain Hardening (Work-hardening).Whats strain hardening ? (working hardening) By strain hardening we means the increase in tensile stress for polycrystals or in shear stress (the flow stress) for single crystals necessary for keeking on

6、 plastic deformation. The shear strain necessary for slip to continue increases with the amount of shear strain. This Phenomenon is called strain hardening or work hardening of single crystal. Strain Hardening curve of single crystal curve. It can be divided in to three stages:for : Easy-glidefor :

7、Linear hardening is very great for : Parabolic hardening flow stress I.Hardening Curve1. Characteristic of hardening curve How to obtain curve .Surface Morphologyslip line slip bandcross slip line and band slip band 滑移带deformation band 形变带 rink band 弯折带4.7 Twinning() Microscopic Aspect. Basic featur

8、e of twinnings. Twinning is a translational movements of one portion of the crystal with respect to the other on a specific plane called twinning plane and along a specific orientation relationship between the two portion of crystals.Twinning system.A Twinning plane plus a twinning direction lying o

9、n it is called a twinning system.Twinning systems for FCC, BCC and HCP.It is more difficult for twinning systems to occur than slip systems, because (twinning).FCC： 111FCC111BCC112BCC： 112ca1a2a3HCP：.Atom movements in twinning of FCC To show movements, all atoms should be projected onto shear plane and contains twinning direction.FCCbasic requirement: symmetrical relationshipDiscussionOrientation relation-ship Be