Lec 2

Lec 2 - ENGR 4250 ENGR 4250 – Advanced Materials...

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Unformatted text preview: ENGR 4250 ENGR 4250 – Advanced Materials Engineering Advanced Materials Engineering Lecture2 Lecture2 Introduction Introduction - 2 eformation Mechanisms Slip System – Slip plane- plane allowing easiest slippage Deformation Mechanisms • Wide interplanar spacings - highest planar densities – Slip direction- direction of movement - Highest linear ensities densities Adapted from Fig. 7.6, Callister 7e. – FCC Slip occurs on {111} planes (close-packed) in <110> directions (close-packed) => total of 12 slip systems in FCC – in BCC & HCP other slip systems occur ELASTIC DEFORMATION 1. Initial 2. Small load 3. Unload bonds stretch turn to δ return to initial F F Linear- lastic Elastic means reversible ! elastic Non-Linear- elastic 2 δ PLASTIC DEFORMATION (METALS) 1. Initial 2. Small load 3. Unload nes bonds planes still sheared stretch & planes shear lastic + plastic δ plastic F δ elastic + plastic Plastic means permanent ! linear lastic linear lastic F 3 δ elastic elastic δ plastic 4 Strategies for Strengthening: 1: Reduce Grain Size • Grain boundaries are barriers to slip. • Barrier "strength" increases with Increasing angle of isorientation dapted from Fig. 7.14, allister 7e. misorientation. • Smaller grain size: more barriers to slip. Adapted from Fig. 7.14, Callister 7e. (Fig. 7.14 is from A Textbook of Materials Technology , by Van Vlack, Pearson Education, Inc., Upper Saddle River, NJ.) • Hall-Petch Equation: 2 1 / y o yield d k − + σ = σ y y 4 Strategies for Strengthening: • Impurity atoms distort the lattice & generate stress....
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Lec 2 - ENGR 4250 ENGR 4250 – Advanced Materials...

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