清华大学：《材料科学基础》课程教学资源（PPT课件讲稿）Chapter 4.1 Introduction

Chapter y Plastic Deformation of Crystal Lesson twelve

Chapter Ⅳ Plastic Deformation of Crystal Lesson twelve

3 1 Introduction 1. Deformation process of polycrystalline materials Deformation process of industrial material consists of three stages Elastic, which is reversible Plastic or permant Fracture

§4.1 Introduction 1. Deformation process of polycrystalline materials Deformation process of industrial material consists of three stages: ➢ Elastic, which is reversible ➢ Plastic or permant ➢ Fracture

2. Deformation mode of crystals 2 )TwInning 3)Grain boundary sliding followed by g b. migration 4)Diffusion

2. Deformation mode of crystals 1) Slip 2) Twinning 3) Grain boundary sliding followed by g.b. migration 4) Diffusion

3. Basic feature of slip and twinning Both slip and twinning are shear processes under shear stresses, i.e. it is a translational movement of one portion of the crystal with respect to the other on a specific plane and along a specific direction

3. Basic feature of slip and twinning Both slip and twinning are shear processes under shear stresses, i.e. it is a translational movement of one portion of the crystal with respect to the other on a specific plane and along a specific direction

slip twinning

slip twinning

The main difference between slip and twinning is that the former does not cause any change in orientation in the sense that any crystallographic direction remain the same with respect to the laboratory coordinate systems. While the latter results in change orientation. After twinning the two parts of the crystal, twinned and untwinned, are symmetrical to some plane or orientation. Or say, one is the twin of the other

The main difference between slip and twinning is that the former does not cause any change in orientation in the sense that any crystallographic direction remain the same with respect to the laboratory coordinate systems. While the latter results in change in orientation. After twinning the two parts of the crystal, twinned and untwinned, are symmetrical to some plane or orientation. Or say, one is the twin of the other

34.2 Slip Systems I Definition Slip Systems is the combination of a crystallographic plane and a direction lying on it. On the plane and along the direction slip takes place A slip plane plus a corresponding slip direction is called a slip system

§4.2 Slip Systems ◆ Ⅰ. Definition： Slip Systems is the combination of a crystallographic plane and a direction lying on it. On the plane and along the direction slip takes place. A slip plane plus a corresponding slip direction is called a slip system.  

l. Slip systems of typical crystals FCC: S.S. (Slip Systems)is (111) at RT (temperature). There are 12 S.S. in all HCP:S.S.{0001}+{1010} for metals with large cla for other HCP metals BCC: 110) (0001) for metals with large cla 12} {123} ( for other HCP metals CsC:{10-100>

◆ Ⅱ. Slip systems of typical crystals FCC: S.S. (Slip Systems) is {111} at R.T. (temperature). There are 12 S.S. in all. HCP: S.S. BCC: CsCl: {110} {0001}1120  + {1010}1120  for metals with large c/a for other HCP metals {123} {112} 111 {110}   {1011} {1010} 1120 (0001) +   for metals with large c/a for other HCP metals

sllp sHip Number of Structure ane direction sp sy Pb, Au, Ag 111610 4x3=12 (111 (111) afe K 321 (111)24×1=24 n(prism 010 (1120) 3×1=3 T, Ma (pyramidal planes 011)(1120)

Schmid's law(The condition for slip to start) 1. The shear stress acting on slip plane along slip direction is T

◆ Ⅲ. Schmid’s law (The condition for slip to start) 1. The shear stress acting on slip plane along slip direction is . 