Material Engineering - EXAM 1

Define precipitation hardening (age hardening)

Process in which the material hardens over a prolonged period of time

How does precipitation hardening increase the strength of a material?

Creates uniformly dispersed microscopic particles inside a materials structure that blocks the movement of dislocations

What is an example of an application that utilizes precipitation hardening?

Internal wing structure

Define a single crystal (monocrystal) solid

Crystal lattice is continuous and has no grain boundaries

Are single crystal solids isotropic or anisotropic?

Anisotropic

Define polycrystal solids (polymaterial)

Many small single crystals with various orientations and contain clear grain boundaries

Describe the anisotropic properties of polycrsytal materials

Contains grains with preferred orientation

Describe the isotropic properties of polycrystal materials

Contains grains with random orientation

Define amorphous solids

No order of the positions of the atoms

Explain how cold work hardening increases the strength of a material

Plasticly deforms a material at room temp

How does cold work hardening effect the structure of a material?

Dislocation motion becomes more difficult after deformation

Explain self diffusion

All atoms that exchange positions are of the same type

Explain interstitial diffusion

Small atoms move through empty spaces between larger atoms

What is an example of interstitial diffusion?

Case hardening

Define atomic packing factor (APF)

Determines the fraction of a unit cells total volume that is filled by atoms vs the remaining space

Define equiaxed grains

Same size in all directions

Define columnar grains

elongated grains

What is a grain refiner?

Controls crystal formation during solidification

How does the addition of a grain refiner affect the final grain structure?

Makes grains smaller and more uniform

If a solute differs in atomic size by >15% from the host, what happens to its solubility?

Contains a low solubility

If a solute has a large difference in electronegativity from the host, what happens to its solubility?

The solute is more likely to form a compound which would limit its solubility

What happens to the solubility of a low valence structure?

Solute is more likely to dissolve in a higher valence

How does the crystal structure affect the atomic diffusion process?

Creates new materials

Define twin boundaries

A reflection of atom positions across the twin plane

Define stacking faults

Errors in packing sequence

Define edge dislocations

One plane of atoms slides over an adjacent plane by defect motion

Define screw dislocations

Motion is perpendicular to direction of stress rather than parallel

True or false: Edge dislocations introduce compressive, tensile, and shear lattice strains

True

True or false: Screw dislocations introduce compressive, tensile, and shear lattice strains

False: screw dislocation introduce shear strain

Define elastic strain recovery

Amount of elastic strain a material will take before reaching a yield point

What happens when a material is unloaded then reloaded after plastic deformation?

Material ends up with a permanent strain and when stress is reapplied the material gets a higher yield point

Explain how reducing grain size increases the strength of a material

Creates more barriers to slip and impedes dislocation motion

Explain shot peening

Produces a compressive residual stress layer and modifies mechanical properties

How does shot peening improve the mechanical properties and fatigue resistance of a material?

Creates plastic deformations causing crystal defects (dislocations)