84.9 Comparison Between Slip and Twinning I. S imi l ar ity Both slip and twinning are shear process under shear stress T ◆‖|. Differences 1. Orientation 2. Atom movement 3.y,△ a)Structure: Twinning is easy 4. Conditions: b) Temperature de d c) Strain rate (or
§4.9 Comparison Between Slip and Twinning ◆ Ⅰ.Similarity: Both slip and twinning are shear process under shear stress . ◆ Ⅱ.Differences: 1. Orientation 2. Atom movement 3. 4. Conditions: , l a) Structure: Twinning is easy b) Temperature: c) Strain rate ) d d (or d d t t
5. Surface morphology Etching treatment with an etchant removes slip steps leaving no trace, but reveals twins by delineating the interface between the twin and the matrix 6. Conditions ① Structure: twinning is easy to take place in crystals of low symmetry ② Temperature dy ③ Strain rate dt 7. Twinning plays an essential role in BCC and HCP lattices
5. Surface morphology: Etching treatment with an etchant removes slip steps leaving no trace, but reveals twins by delineating the interface between the twin and the matrix. 6. Conditions: ① Structure: twinning is easy to take place in crystals of low symmetry. ② Temperature ③ Strain rate dt d 7. Twinning plays an essential role in BCC and HCP lattices
34.10 Basic Features of The Plastic Deformation of Polycrystals Basic distinction between single crystal and polycrystals (1 A great deal of grains with different orientation ② Grain boundary G B is a thin layer of material between neighboring grain where atoms arranged in transitional position
§4.10 Basic Features of The Plastic Deformation of Polycrystals Basic distinction between single crystal and polycrystals ① A great deal of grains with different orientation ② Grain boundary G.B. is a thin layer of material between neighboring grain where atoms arranged in transitional position
grain gr rain boundary single crystal polycrystal
single crystal polycrystal grain grain boundary
I Grain boundary and its role i deformation (1 Impede slip(as obstacles)at R.T. and low temperature 2 Coordinate the deformation in different grains 3 Enhance(assist) the plastic deformation at high temperature through grain boundary sliding There exists an Equicohesive Temperature at which grain Ob(g b)=ob(grain T≈0.5T
◆ Ⅰ.Grain boundary and its role in deformation ① Impede slip (as obstacles) at R.T. and low temperature. ② Coordinate the deformation in different grains. ③ Enhance (assist) the plastic deformation at high temperature through grain boundary sliding. b graing.b. Tet T There exists an Equicohesive Temperature at which b(g.b.) = b(grain) Tet 0.5Tm