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10 Cards in this Set
- Front
- Back
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Alloying: substitution of atoms |
Solute atoms replace solvent atoms Solvent and solute atoms need to follow HUME ROTHERY RULES: 1) Appox same size 2) Same preferred crystal structure 3) Same number of valence electrons 4) similar electronegativity |
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Alloying: addition of small atoms |
Small atoms occupy interstitial sites Diameter of solute atoms less than 60% of solvent atoms Most useful C in FE Solubility limit: when all the interstitial sites are filled |
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Strengthening of metals: Solid Solution Hardening |
Dislocation: imposes strain field Atoms above dislocation-compressed Atoms below dislocation- tension strain field Field attract solute atoms to reduce overall strain mismatch Smaller solvent atoms: impose tensile strain, go to compressive part of dislocation strain field Larger solvent atoms: impose compressive strain, go to tensile part of dislocation strain field *More energy required to move dislocations |
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Strengthening of metals: Precipitation Hardening (Theory) |
Dislcated impeded by second solid phase Non equilibrium process (not enough time) forms small precipitates E.g. Rapid cooling does not allow atoms to fully diffuse to form equilibrium phase Forms supersaturated solution |
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Strengthening of metals: Precipitation Hardening (Method) Example: Aluminium Copper Alloy |
1) Solution treat the alloy- form single phase solid solution 2) Quench- supersaturated solution (soft single phase but unstable) 3) reheat alloy and hold so atoms diffuse 4) Cool alloy to room temperature |
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Measuring tensile properties of ceramics |
Specimen are difficult to grip and prepare Very small failure strains (after 0.1% strain) Use 3 or 4 point bending top surface of specimen is placed under compression max tensile stress exist at the bottom surface below the point of load application |
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Manufacturing of advanced ceramics |
1) Ceramics particles mixed with binding agent (water) 2) Forced into shape under pressure 3) Pressed component is sintered (heat so grain boundaries will coalesce) *leave spherical pores that lead to low toughness |
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Polymerisation |
Chains of atoms held together by covalent bonds manomer molecules react to form the polymer use of ehylene (C2H4) --> Polyethylene (PE) |
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Semi crystalline polymers |
polymers containing both crystalline and amorphous regions Long LINEAR chains folding so regular packing between the chains can form Thermoplastics such as PE will behave like strands of spaghetti and be tangled |
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Amorphous polymers |
Long branched chains and networks prevents crystalline regions (cannot fold) |
