Chapter_1b_Lengthscales - Part of MATERIALS SCIENCE...

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MATERIALS SCIENCE MATERIALS SCIENCE & ENGINEERING Anandh Subramaniam & Kantesh Balani Materials Science and Engineering (MSE) Indian Institute of Technology, Kanpur- 208016 Email: [email protected], URL: home.iitk.ac.in/~anandh AN INTRODUCTORY E-BOOK AN INTRODUCTORY E-BOOK Part of http://home.iitk.ac.in/~anandh/E-book.htm http://home.iitk.ac.in/~anandh/E-book.htm A Learner’s Guide A Learner’s Guide A Learner’s Guide
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The Issue of Lengthscales The Issue of Lengthscales To understand structure sensitive properties (yield strength, fracture toughness etc.) we may have to traverse across various lengthscales. We have already seen in the Introduction chapter that we have to traverse across lengthscales to reach the scale of the component starting with the scale of the atoms (as repeated in the next slide) . When we traverse across lengthscales we get different perspectives of properties. Order, properties, etc. may seem very different at different lenghscales. These aspects are considered by looking at some examples. Please also revise the issues related to global vs local Please also revise the issues related to global vs local
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Atom Structure Crystal Electro- magnetic Microstructure Component Thermo-mechanical Treatments Phases Defects + Casting Metal Forming Welding Powder Processing Machining Vacancies Dislocations Twins Stacking Faults Grain Boundaries Voids Cracks + Residual Stress Processing determines shape and microstructure of a component & their distribution Travel across lengthscales to reach the scale of the component
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Unit Cell * Crystalline Defects Microstructure Component *Simple Unit Cells Angstroms Dislocation Stress fields Nanometers Microns Centimeters Grain Size Lengthscales in Materials Science Lengthscales in Materials Science Let us start with a cursory look at the lengthscales involved in Materials Science ( Notes in the next slide )
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Unit cells of simple crystals are a few angstroms (though there might be crystals with large unit cells– examples of these may be found in Chapter 4) Dislocations are crystalline 1D defects (Chapter 5) with long range stress fields (i.e. they extend to the extent of the crystal). However, the ‘effective’ region of a dislocation stress field may be perceived to be a few tens of nanometers.
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