Chapter5 - Chapter 5 Linear, Planar, and Volume Defects...

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Chapter 5 Linear, Planar, and Volume Defects • Introduction • Linear Defects, Slip and Plastic Deformation • Planar Defects • Volume Defects • Strengthening in Metals
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Introduction Chapter 5 • In the previous chapter, point defects were shown to strongly influence properties. • It was hypothesized in the 1930’s and demonstrated experimentally in the 1950’s that crystals contained line defects and the mobility of the defects controls strength. • The line defects account for the dramatic difference between the strength of perfect crystal and a real crystal with defects.
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Introduction Chapter 5 • In addition to line defects, there are also planar and volume defects that also affect the strength and other properties of a material. • The emphasis in this chapter will be on metallic and ceramic materials because of their highly crystalline nature.
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Normal Force Shear Force
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Model to Calculate Theoretical Critical Resolved Shear Strength Macroscopic view Atomic scale view Broken plane of atoms
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Edge Dislocation Edge dislocation line Extra half plane of atoms
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Edge Dislocation Dislocation glide
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Role of Dislocations in Plastic Deformation τ τ
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Transmission Electron Microscopy (TEM) Image of a Collection of Dislocations
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Burgers and Burgers Vector for an Edge Dislocation D i s l o c a t n e Start=End Burgers Vector End Start
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Types of Dislocations Edge Screw Mixed Loop
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Rug Axis of the ripple Direction of applied force Ripple in the Rug Analogy to a Dislocation D i s l o c a t n e Burgers vector
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Burgers Vectors and Slip in FCC Crystals These vectors are the Burgers vectors in the FCC system since they connect the atoms of closest approach. { } 111 These planes correspond to the planes of densest packing in the FCC structure. 110 2 o a
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Burgers Vectors and Slip in FCC Crystals 110 2 o a 110 2 o a 011 2 o a 2 o a 101 2 o a 101 2 o a ⎡⎤ ⎣⎦
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Burgers Vectors and Slip in FCC Crystals These vectors are the Burgers vectors in the FCC system since they connect the atoms of closest approach. { } 111 These planes correspond to the planes of densest packing in the FCC structure. 110 2 o a
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Tetrahedron in a Cubic Unit Cell- Geometry of FCC Deformation x y zG e o m e t r y There are 4 faces on the tetrahedron these are the close packed planes The six edges of the tetrahedron are the directions of closest approach of the atoms
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Tetrahedron in a Cubic Unit Cell- Geometry of FCC Deformation x y z 0,0,0 1,1,1 Using intercepts the plane is (111) In a cubic crystal the vector normal to the plane has the same indices as the plane. 0,0,1 1,0,0 101 ⎡⎤ ⎣⎦ 0,1,0 011 a b Vector normal is a x b .
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Chapter5 - Chapter 5 Linear, Planar, and Volume Defects...

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