Material Science Midterm 2 Review

Advantages of cold working

High quality surface finish

Mechanical properties may be varied

Close dimensional tolerances

Disadvantages of cold working

High deformation energy requirements

Large deformations must be accomplished in steps which can be expensive

Loss of ductility

Sources of residual stresses in metal components are

Plastic deformation processes

Nonuniform cooling of a piece from a piece that was cooled from an elevated temperature

Phase transformation in which parent and product phases have different densities

Advantages of hot working

Large deformations are possible which can be repeated

Deformation energy requirements are relatively low

Disadvantages of hot working

Poor surface finish

Variety of mechanical properties isn’t possible

Adverse consequences of residual stresses in metal components are

Distortion and fracture

For refractory ceramic materials, three characteristics that improve with increasing porosity are

1. decreased thermal expansion and contraction upon thermal cycling,

2. improved thermal insulation, and

3. improved resistance to thermal shock.

Characteristics that are adversely affected when increasing porosity in refractory ceramic materials are

1. load-bearing capacity and

2. resistance to Attack by corrosive materials.

The glass transition temperature for a noncrystalline ceramic is

that temperature at which there is a change of slope for the specific volume versus temperature curve.

The melting temperature for a crystalline material upon cooling is

that temperature at which there is a sudden and discontinuous decrease in the specific-volume-versus temperature curve.

A Frenkel defect will cause a change in

apparent cation location

When cooling from liquid, glassy materials form __ based on __

gradually, specific volume

__ iron is used in applications with high vibrational energy.

Malleable

The term annealing describes a heat treatment used to

Relieve stresses

Specific volume (v)

Volume per unit mass

Plastic deformation of a polycrystalline metal doesn’t increase density

True: changes shape and internal structure not mass or volume

Critical stress for crack propagation is applicable for ductile and brittle materials

Only applies to brittle materials, ductile materials go through plastic deformation and have more yielding and toughness

Austenite → pearlite

Slow cooking

Austenite → Bainite

Moderate cooling

Austenite → martensite

Rapid quenching

Austenite uses diffusion for pearlite and bainite

Carbon atoms must diffuse to form alternating layers of ferrite and cementite. Martensite doesn’t diffuse

Austenite containing 1.2 wt% is cooled slowly, will hypereutectoid form above 727C?

Eutectoid temp. For steel is 727C, above this it’s just Austenite w/ carbon in solid soln. Fe3C forms below 727C

Thermal stress

Stress induced due to temp. Changes, expansion or contraction is restricted

Annealing

Apply constant heat (lower than melting point) and cool slowly

How does annealing affect the tensile modulus of an undeformed semicrystalline polymer?

Increases tensile modulus by rearranging polymer chains increasing crystallinity and tightly packing and ordering regions

How does annealing affect the tensile modulus of a drawn semicrystalline polymer?

Decrease tensile modulus by relaxing and recoiling oriented chains; Lose alignment and return to less ordered state reducing stiffness

Annealing of glass

Heating below glass transition then slowly cooling, relieves internal stress, less brittle and more stable.

Tempering of glass

Heating above transitioning temperature then rapid quenching; controlled residual compressive stresses, tougher, better strength and impact resistance (adds stress)

Hardenability

Ability to form martensite upon quenching

How does pearlite form?

High temp., slow cooling; fast cooling → fine pearlite; slower cooling→ coarse pearlite

550C-727C

How does bainite form?

Low temp., moderate cooling; longer time

220C-550C