Imperfections in Solids (고체의 결함) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University

OCW 19. Point defects 20. Edge Dislocation 21. Screw Dislocation https://youtu.be/EuUJApDftkI?list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm 20. Edge Dislocation https://youtu.be/DW96k-iEwYA?list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm 21. Screw Dislocation https://youtu.be/Lc9KoCMpcWU?list=PL8EAOgbez9XIWGbmcihctMO4bXSB4V8hm Optical microscope https://youtu.be/L3SsxIUm0As Scanning electron microscope https://youtu.be/GY9lfO-tVfE Scanning tunneling microscope https://youtu.be/wNEqRq6NyUw

KOCW 결정질 고체의 구조 4 결정질 고체의 구조 5 http://www.kocw.net/home/cview.do?lid=bd0335a131743ff1 결정질 고체의 구조 5 http://www.kocw.net/home/cview.do?lid=2c394709f4d570d1

Impurity(불순물) of Solids Point Defects (점결함) Vacancy(공공) vacant atomic sites in a structure Interstitial(침입) solid solution Substitution(치환) solid solution Solid solution(고용체) increase strength(강도) Impurity(불순물) of Solids Vacancy in ceramic Interstitial C in Fe Substitution Cu in Ni

Dislocation (전위) A irregularity within a crystal structure Increase yield strength(항복강도) and decrease ductility(연성) In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials. An edge dislocation is a defect where an extra half-plane of atoms is introduced mid way through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, this extra plane passes through planes of atoms breaking and joining bonds with them until it reaches the grain boundary. A screw dislocation is much harder to visualize. Imagine cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect. If the cut only goes part way through the crystal, and then slipped, the boundary of the cut is a screw dislocation. edge screw

Interfacial(계면) Defect Grain boundaries of polycrystalline materials control crystal slip Grain boundary increase strength 계면결함은 2차원이며 다른 결정 구조 또는 다른 결정 방향을 가진 재료의 두 영역을 분리하는 경계면을 말함 외부표면, 결정립계 상계면 쌍정립계 적층결함 이 있음 외부표면은 가장확실히 볼수있는계면 , 결정구조의 연속성이 종료되는 계면이다 표면의 원자는 최대수로 결합되어 있지않아 높은 에너지상태로 존재하고 , 이러한 표면의 불한전한 결합 상태는 표면 에너지를 유발합니다. 재료는 표면 에너지르 최소화하기위해 가능한 표면적을 최소화 하려고 하는데…이로인해 외부표현이 발생합니다. 결정립계의 계략도 경정립계는 수개의 원자 거리폭과 각도를 가지며 한 결정립의 결정 방향에서 이웃하는 결정립의 결정방향으로 넘어갈때 상당한 원자 불일치가 존재한다 불일치가 작을 때(각도) 소각 결정립계 클때 고각결정립계

Optical microscopy (광학현미경) https://youtu.be/L3SsxIUm0As

SEM STM SEM: Scanning Electron Microscope (전자현미경) STM: Scanning Tunneling Microscope

Summary Point defects Edge dislocation Screw dislocation Optical microscope (grains) Scanning electron microscope (grains) Scanning tunneling microscope (atom)