AML 883 Properties and selection of engineering materials
LECTURE 1. INTRODUCTION
M P GururajanEmail: [email protected]
Room No. MS 207/A3 Phone: 1340
A request!
Please send me a mail at (with subject AML 883)[email protected]
All your assignments, problem sheets, presentations (after the lecture, if you request) as well as the accouncements regarding the class
will be mailed to you at your mail address.
Introduction to the course!
Textbook
● Mateials: engineering, science, processing and design, M F Ashby, H Shercliff and D Cebon, ButterworthButterworthHeinemann, 2007Heinemann, 2007
● A low priced Indian edition is available.
Grading policies
● Assignments and/or quizes: 20%● Two midterm examinations: 40% (20+20)● Final examination: 40%● Problem sheets – not necessary to turn in;
however, a fraction of questions for the exams will come from the problem sheets, directly!
What are we going to study?And, How?
A stadard cell in a chip● Rendering of a small standard
cell with three metal layers (dielectric has been removed). The sandcolored structures are metal interconnect, with the vertical pillars being contacts, typically plugs of tungsten. The reddish structures are polysilicon gates, and the solid at the bottom is the crystalline silicon bulk.
● Image courtesy: wiki (David Carron)
Types of materials● Crystalline silicon bulk at the
bottom – gives structural support
● Interconnects, contacts, dielectrics and polysilicon gates – have specific functions in terms of electrical conduction or nonconduction
A broad classification
Based on the specific role in an engineering application
• Structural materials (mechanical)• Functional materials (electrical, optical,
magnetic, ...)
Structural materials
● Stiffness – Resistance to elastic deformation (A wooden ruler is stiff, while a plastic one isn't)
● Strength – Resistance to plastic deformation (A metallic ruler is strong, while a plastic one isn't)
● Toughness – Resistance to fracture (A plastic ruler isn't tough, while wooden and metallic are)
● Properties Mechanical ● Density, elastic modulus, yield strength, fracture
toughness, fatigue resistance, ...
Functional materials
● Conductors, insulators and dielectrics (electrical materials?) Conductivity, dielectric constant
● Magnetic materials – remanence, saturation magnetization
● Optical materials – transmission, reflection, refraction, ...
Structural versus functional
● Mylar: good, structurally; bad, functionally (undergoes resistive degradation with increasing temperature and humidity)
● 32 sheets in 0.45 mm● Image courtesy: wiki
Structural versus functional
● High Tc oxide ceramic superconductors – BSCCO (bisko) – Bismuth Strontium Calcium Copper Oxide: good, functionally; bad, structurally (brittle)
● Image courtesy: wiki
Variety in materials/geometry
Image courtesy: wiki
Variety in materials/geometry
Image courtesy: Caltech Engineering Design lab handout
Processing
● Different materials – should be processed differently;
● Same material should be processed differently for different geometries (spokes or rim or frame);
● Apart from material properties and geometry, the number of components and the specifics of use (where? under what conditions? under what constraints? how costly?) determine the processing routes chosen
Processing: the other story
● Processing can change (at times dramatically) the properties
● How to come up with new processes with desired property combinations?
● Arises the need for fundamental understanding
Valiev et al, Journal of Materials Research, 2002.
Materials selection: considerations
● Engineering considerations (discussed above)● Cost● “Green” Can this be considered as part of
cost?● Easy commerical availability in large quantities
(Case study of fan blades)● Political (Sanctions on nuclear materials)● Technology (Cryogenic engines, for example)
A break! Superalloy?!
A humorous take on “Super” alloy!Image: Courtesy of HKDH Bhadeshia, University of Cambridge homepage
Materials in service: wear
Photos from a pump repair company homepage (Emnor Mechanical Inc., Canada)
Corrosion and oxidation
Corroded Titanic bow, rusted baking plate and bolts (Image courtesy: wiki)
Degradation at high temperatures
TBC on Nibase superalloy turbine blades and their effectiveness during serviceImages: courtesy University of Cambridge homepage
The unseen damages!
Original microstructure and rafted microstructure in Nibase superalloysImages: courtesy University of Cambridge homepage
Material degradation
● Physical – Wear● Chemical – Oxidation and corrosion● Thermal and micorstructural – creep, faster
oxidation, rafting, ...
Materials property charts
● Density and Young's modulus of classes of materials
● Image courtesy: University of Cambridge hompeage
Materials property charts
● Young's modulus and cost of classes of materials
● Image courtesy: University of Cambridge hompeage
Materials property charts
Image courtesy: University of Cambridge homepage
Topics of study
● Structural materials and their properties● Functional materials and their properties● Processes and properties● Material degradation● Property charts
Case studies
(1) Materials for blades of fans in windtunnels (structural)
(2) Mylar insulation in aircraft wirings (functional)
(3) ECAP and cryorolling (processing)
(4) Thermal barrier coatings for jet engine turbine blades (degradation)
(5) Material property charts for metallic glasses (Charts as tools)
(6)Materials for Solid Oxide Fuel Cells (SOFC)
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