Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
MEE 312 Final Study
| Question | Answer |
|---|---|
| What are some general characteristics of metals and alloys? | ferrous and non-ferrous Moderate melting temperature good ductility moderate strength good electrical/thermal conductivity |
| What are some general characteristics of ceramics? | Crystalline poor ductility high strength brittle |
| What are some general characteristics of polymers? | low melting temp poor electrical/thermal conductivity low strength thermoplastics, thermosets, elastomers |
| What are some general characteristics of composites? | engineered properties two or more materials |
| mechanical properties | response to an applied force, microstructure sensitive (strength, ductility) |
| physical properties | materials response to applied field, microstructure insensitive (modulus, CTE, conductivity) |
| Primary bonds (types) | covalent ionic and metallic |
| Secondary bonds (types) | Van der Waals |
| What are covalent bonds? | sharing of valence electrons, strong bond (high strength, low CTE, high melting temp, high E); no free electrons, so low conductivity; examples: ceramics, bonds within molecular chains |
| What are ionic bonds? | strong electrostatic attraction b/w anion and cation, strong bond (same characteristics of covalent bond) example: ceramics |
| What are metallic bonds? | outermost electrons given up to form electron cloud, relatively weak bond (lower strength, high CTE, low melting temp, low E); many free electrons (good conductivity) |
| What are secondary bonds? | weak electrostatic attraction that results from polarity in molecules |
| amorphous | no long range order |
| crystalline | long range order |
| three most common types of unit cells | FCC, BCC, HCP |
| FCC characteristics | low strength high ductility ex: aluminum |
| BCC characteristics | moderate strength moderate ductility ex: steel |
| HCP characteristics | high strength low ductility example: some titanium |
| close packed direction | where atoms are all touching |
| BCC close packed planes (BCC) | BCC does not have any close packed planes |
| How do point defects affect the material's strength and ductility? | they disrupt the perfect arrangements of atoms in the crystal and act as a barrier to slip |
| How and why do surface defects affect a material's strength and ductility? | they disrupt the perfect arrangements of atoms in the crystal and act as a barrier to slip |
| How can some defects be controlled? | Inoculation: smaller grains and more grain boundaries, therefore more barriers for slip faster cooling rate: smaller grains, dispersion strengthening phase boundaries |
| What are the two different mechanisms for diffusion? | interstitial and vacancy |
| Interstitial diffusion | smaller species, more sites, lower activation energy (fast) |
| Vacancy diffusion | fewer sites, but increase exp with temperature, larger species, higher activation energy (slow) |
| Factors that affect diffusion in materials | type and mechanism of diffusion temp crystal structure (the more open, the faster the rate) bonding (strong bonds have slower rate) |
| What are the types and rates of diffusion? | Surface (fastest) Grain boundary (moderate) Volume (slowest) |
| How does diffusion relate to grain growth? | The factors that affect diffusion will affect all diffusion controlled phenomenon such as creep, heat treating, and processing |
| How does hardness data relate to tensile data? | As hardness increases so does strength |
| Two types of hardness tests | Rockwell and Brinell |
| How can we determine the toughness based on a stress strain curve? | Area under the curve |
| What is cold working? | Plastically deforming a material, simultaneously shaping and hardening it |
| What is the effect of strain hardening? | Creates more dislocations which are line defects, and these defects disrupt perfect arrangement of atoms |
| What is the difference associated with the strain hardening of polymers and metals? | For polymers, we are aligning chains, NOT increasing number of dislocations (no dislocations in amorphous materials) |
| What are the three stages of annealing? | Recovery, Recrystallization, Grain growth |
| recovery | low temperature treatment rearranges dislocations to a polygonized subgrain structure strength does not change electrical conductivity restored residual stresses eliminated |
| recrystallization | new grains nucleate on boundaries of dislocations strength decreases ductility restored dislocation decreases |
| grain growth | new grains grow fewer grain boundaries decrease in strength |
| How does hot working compare to cold working? | Hot working is done above the recrystallization temp, so the material is annealed as it is deformed. There is no change in properties |
| What are the two steps with solidification? | nucleation and growth |
| homogeneous nucleation | spontaneous clustering of atoms forms a nucleus that is large enough to grow only in lab conditions |
| heterogeneous nucleation | formation of a nucleus on the surface of an impurity, occurs most frequently |
| What is solid solution strengthening? | addition of point defects, forms a solid solution |
| What is dispersion strengthening? | solubility limit is exceeded so that a second phase forms, phase boundaries act as a very effective block to slip increase in strength (non coherent precipitate) |
| What type of materials are used in age hardening? | mostly non ferrous metals and stainless steels |
| How and why does age hardening affect a material's properties? | tricks the material into forming a coherent precipitate, more effective at blocking slip significant strengthening |
| What are the three steps in age hardening? | Solution treatment Quench Age |
| Solution treatment | heating a material to a single phase solid solution |
| Quench | cool rapidly to prevent diffusion of atoms to nucleation sites, so the second phase cannot form (supersaturated solid solution) |
| Age | naturally - at room temp artificially - at temp above room temp but above the solvus allows diffusion so that a coherent precipitate of a second phase forms |
| overaging | occurs during artificial aging, coherent precipitate breaks free from parent lattice, becomes non coherent and a decrease in strength occurs |
| Three major types of microconstituents | pearlite bainite martensite |
| pearlite | slow cooling rate lamellar structure of ferrite and cementite lower strength, good ductility |
| bainite | moderate cooling rate fine layered structure of ferrite and cementite moderate strength, moderate ductility |
| martensite | fast cooling rate forms BCT structure through a twinning process very strong but brittle it is tempered to allow diffusion to occur and form a fine microstructure of ferrite and cementite with high strength and useable ductility |
Created by:
flyerbud
Popular Engineering sets